When choosing one or another roof shape for a future home, the owner actually determines the type of its rafter system. The effective functioning of the entire roofing structure, and ultimately the longevity of the house and the comfort of its inhabitants, depend on the correct choice, competent calculation and installation.

The concept of a mansard roof

Houses with a mansard roof (attic) differ from other types of residential buildings, although they are often confused with two-story or attic buildings.

Mansard roofs are very different in design from conventional ones.

The attic, like a full floor, is a residential superstructure. It is included in the registration certificate of the house and has utilities installed - heating, plumbing, lighting. The main difference lies in the design features of the structure:

• floor - a tier with walls identical around the entire perimeter on which the rafters rest;
• attic - an under-roof space, the height of which varies under the slopes.

Thus, the attic roof is the walls of the upper floor and at the same time the roof of the house, which is clearly visible in the exterior of the building.

A house with a mansard roof looks interesting and stylish, while a full-fledged multi-storey private house is respectable and more reminiscent of urban facilities

The height of the attic is regulated by standards - at least 1.5 m - which distinguishes it from the attic roof. In reality, the developer chooses the height of the attic space, taking into account:

• strength of foundation and walls;
• wind and snow loads on the roof;
• purpose of the attic;
• architectural style of the house;
• comfort of staying in the attic room.

All these nuances are discussed at the stage of designing the house and, according to the result, the roof truss system is selected.

Video: rafter systems, what determines the price and complexity of manufacturing

Types of rafter systems for attic roofs

Mansard roofs today are presented in different formats and, accordingly, have different rafter system designs.

Modern construction technologies make it possible to equip an attic under any roof, but you need to understand that the efficiency of using the under-roof space will be different.

The following types of attic roofing systems are distinguished:

1. Single-pitched mansard roofs are simple structures that are most often erected on small houses, since the arrangement of a large slope will require strengthening the rafter frame and increasing the cost of roofing materials.

   An attic in a house with a pitched roof must be planned in advance so that during the construction stage the lower point of the slope is raised at least 1 m above the ceiling

2. Gable roofs are the most popular among all types, as they are economical and easy to install. The supporting frame consists of straight parallel rafters connecting the walls and the ridge girder. However, their slope limits the usable area of ​​the attic, which in some cases makes it difficult to use. Although recently designers have been using the asymmetry of gable roofs, which partially solves the problem.

   Roofs consisting of two slopes with triangular gables are the most popular option for all types of buildings, both with and without attics.

3. Sloping roofs are a type of gable roof system with different slopes, thanks to which you can create a spacious and comfortable area under the roof. The basis is made up of rafters divided into several parts, which, when connected, form a concave or convex broken line, which is used by designers to stylize the exterior. Broken attics have the greatest height, and rooms without sloping walls are no different from ordinary rooms.

   The broken structure is the most effective and simple; these are the roof shapes that were originally called attics

4. Hip, half-hip and vaulted are unique mansard roofs with a large number of pitched breaks, which allows you to create spacious rooms with acceptable high ceilings. Such structures look unusual and very attractive, but they have a complex rafter system, the construction of which will require experience, knowledge and large financial costs.

   A mansard hip roof of complex configuration requires accurate calculations of all loads on the foundation and walls of the building

5. Hipped attics - have 4 or more identical slopes and are suitable for square-shaped houses. Under such structures it is easy to arrange a living room, in which the greatest height will be in the middle, and the edge space will be limited in use due to low ceilings.

   Hipped mansard roofs give buildings extraordinary attractiveness

6. Multi-gable and combined structures - usually such roofs are erected on houses with complex architecture. They have several gables, are amazingly beautiful, drain precipitation well and are distinguished by excellent resistance to mechanical loads. The multi-gable rafter system is very unique. It can be made from either hanging or layered rafters (if there is a permanent internal partition). In addition, it consists of several departments, making the house look unusual and presentable. In most cases, several attic rooms are installed under such roofs, where the size of each depends on the specific rafter section.

   Complex multi-gable roofs resemble an origami flower, which is why architects love to use these structures, although they are much more difficult to manufacture and maintain than other types

The main difficulty when choosing an attic is the variety of its geometric shapes and placement possibilities.

Broken and triangular, occupying the entire area of ​​the house or only a part, facing both sides or one, symmetrical and asymmetrical attics differ in location relative to the external walls of the building, which directly affects the complexity of the rafter system, its manufacture and installation.

They can be of a corridor type, sectional or mixed, located both inside and outside the walls with a slight extension of the lower floor or significant, requiring the formation of additional supports in the form of walls, pendants, columns.

Any attic looks aesthetically pleasing and adds completeness to the building.

Be that as it may, the creation of attics comes down to three types:

Video: broken rafter system for an attic roof

https://youtube.com/watch?v=nENtDpL0m5E

Features of the attic rafter system

The supporting frame is the basis on which the reliability of the attic roof depends. It includes:

1. Hanging rafters. They rest on the external walls and are joined together at the ridge girder. Rafters of this design do not need a mauerlat - to horizontally level the walls, it is enough to lay a board on top of the roofing felt. This provides significant savings on lumber. In addition, there is no need to install intermediate supports with a span width of up to 6 m, which allows you to get free studio space. The thrust load is neutralized by puffs laid at the very base or higher (raised). The lifting of the tie must comply with building codes, since the strength of the structure depends on this. For larger spans, the frame is reinforced with headstocks, crossbars and struts.

   If the building does not have permanent internal walls, then hanging rafter systems are used

2. Layered rafters. This is a more reliable design, used mainly for long-span buildings. The rafters rest on the ridge purlin (above), side purlins, and also on the walls. Reinforced with puffs and braces. But with this design of the rafter base, the attic space is limited by the size and location of the racks - in the center, symmetrically along the edges or shifted to one side. Although it is the racks that make it possible, if desired, to stylishly zone the room.

   The layered structure is more profitable and not as heavy as with hanging rafters, which is why less materials are required for its arrangement

3. Mixed rafters. As a rule, they are used in broken structures. The lower part is mounted according to the scheme of layered rafters and is crowned with a triangle of hanging rafter legs, where the tie simultaneously serves as the attic floor beam.

   The mixed structure of the rafter frame is mainly used in the construction of broken attic roofs

The differences between the attic rafter system are:

Intervention in the design of the supporting frame and any changes to suit personal preferences and design imagination require thorough calculations.

Calculation of the load-bearing structure for a mansard roof

Video: designing a rafter frame in SolidWorks and ArchiCad

We will look at how to calculate the rafter system yourself, which will allow any developer, having a basic understanding of the calculation process, to control the design and progress of construction. We will do the calculation using a simplified method so as not to concern aerodynamics and strength of materials.

We draw a sketch of the house on paper and display on it the parameters necessary for the calculation:

The house is being built in Kazan (private sector within the city). We took all the initial data arbitrarily to show the calculation procedure with an example.

• variables - wind, snow and those caused during roof maintenance;
• constant - the weight of the roofing filling (pie) and the equipment planned for installation;
• fatal - earthquakes, floods, etc., which are rare, so there is no point in calculating them; it is enough to add 5–10% to the total loads.

We carry out the calculation, guided by the collection of rules numbered 17.13330.2011 and 20.13330.2011 with regional load distribution maps included in it, as well as standards 2.01.07–85.

Wind load

We calculate wind pressure using the map, the corresponding tables, and also using the formula W m = W o x k x c, where:

Table: k indicator according to SNiP 2.01.07–85 for various types of terrain

Building height Z, m	Coefficient k for terrain types
	A	IN	WITH
≤ 5	0,75	0,5	0,4
10	1,0	0,65	0,4
20	1,25	0,85	0,55
40	1,5	1,1	0,8
60	1,7	1,3	1,0
80	1,85	1,45	1,15
100	2,0	1,6	1,25
150	2,25	1,9	1,55
200	2,45	2,1	1,8
250	2,65	2,3	2,0
300	2,75	2,5	2,2
350	2,75	2,75	2,35
≥480	2,75	2,75	2,75
Note: “A” - open coasts of seas, lakes and reservoirs, as well as deserts, steppes, forest-steppes, tundra; “B” - urban areas, forests and other areas evenly covered with obstacles more than 10 m high; “C” - urban areas with buildings over 25 m high.

Since the wind force sometimes reaches impressive levels, when erecting a roof, especially an attic one, due attention must be paid to the reliable fastening of the rafters to the base.

We substitute the data into the formula W m = W o x k x c, taking into account that Kazan belongs to region I (according to the map), the height of the building is 6514 mm, construction is carried out within the city, but in the private sector without the presence of high-rise buildings nearby. So, 24 x 0.65 x 0.8 (if the slope of the slopes is ≥ 30°, then the wind presses on the roof, then according to the standards 2.01.07–85 clause 6.6, the largest aerodynamic indicator is taken into account) ≈ 13 kg/m².

There is little antenna-mast equipment on the roofs of private buildings, and modern covering materials are characterized by high heat and frost resistance, due to which climatic and ice loads are, as a rule, not calculated for them.

Snow load

On the snow load distribution map, we find the value for Kazan (240 kg/m²) and substitute it into the calculation formula S = µ x S g, where:

There is a small nuance here - if it is impossible to measure the slope of the slopes (for example, a house is being built from scratch, and there is no supporting frame yet), then the values ​​of the angles should be determined from the table, based on the span width (L) and the planned height of the building from the floor to the ridge (H ).

According to the basics of trigonometry, the tangent of the angle of inclination (tg α) is calculated as the ratio of the height to half the length of the span or to the full length for a pitched roof

Table: ratio of house size and slope slope

Determining roof slope
H value:½ L (tg α)	Angle α°
0,27	15
0,36	20
0,47	25
0,58	30
0,7	35
0,84	40
1	45
1,2	50
1,4	55
1,73	60
2,14	65

Let's move on to our parameters: 3514: ½ 6600 = 1.06, which means the lower tilt angle will be approximately 47°, and (3514 - 2200) : ½ 4050 = 0.649, i.e. the upper tilt angle will be approximately 32°.

The correction value depends on the roof slope:

• if the slope angle (α) ≤ 30°, then µ = 1;
• if the angle α ≥ 60°, then µ = 0 - the snow load is not calculated, since snow does not linger on steep slopes;
• if 30°< α < 60°, то µ высчитывают по формуле → µ = 0,033 х (60 - α).

Therefore, the correction factor for a slope slope of 47° will be calculated using the formula 0.033 x (60–47) = 0.429. Thus, the snow load is 0.429 x 240 ≈ 103 kg/m².

Roof load

The attic structure has a typical roofing pie:

Its layers in one way or another exert pressure on the supporting frame. Usually, in a simplified calculation, all layers of the roofing filling are taken into account, which leads to strengthening of the supporting structure, but also to its rise in cost. However, all layers exert pressure only when an attic is built with decorative exposed rafters and all roofing materials are laid on top of them.

One of the ways to arrange an attic is that the wooden elements of the rafter system remain open and serve as interior decoration

With a standard roofing pie structure, insulation, vapor barrier, retaining supports and sheathing can not be taken into account in calculating the roof load, since they are placed between the rafters and under them. However, to calculate the Mauerlat, they also need to be taken into account. This division is relevant for the calculation of large roofs, where the difference in cost will be significant.

Having decided on the covering material in advance, it is easy to calculate the weight of the roof, focusing on the technical parameters declared by suppliers.

Table: average weight of roofing materials:

Name of material	Weight, kg/m²
Ondulin	4–6
Bituminous shingles	8–12
Slate	10–15
Ceramic tiles	35–50
Corrugated sheet	4–5
Cement-sand tiles	25–45
Metal tiles	4–5
Slate	45–60
Rough flooring	18–20
Layered wooden rafters and purlins	15–20
Hanging rafters under a cold roof	10–15
Wood sheathing	8–12
Bitumen	1–3
Polymer-bitumen waterproofing materials	3–5
Ruberoid	0,5–1,7
Insulating films	0,1–0,3
Plasterboard sheets	10–12

Let's return to the example again and calculate the load from the roof, taking into account that we will cover the roof with metal tiles and leave the rafters open. Weight of layers of roofing pie without insulation = 5 (metal tiles) + 5 (polymer-bitumen insulation) +12 (lathing) + 12 (plasterboard) + 0.3 + 0.3 (hydro- and vapor barrier films) ≈ 35 kg/m².

To calculate the thickness of the insulation, there is a formula T = R × λ, where:

We choose Isover “Pitched Roof” slabs as insulation. Then T = R × λ = 4.95 x 0.04 = 0.198 m. Multiplying the thickness by the density of the material indicated in the technical specifications, we obtain its specific gravity → 0.198 m x 15 kg/m³ ≈ 3 kg/m². Therefore, the total roof load = 35 + 3 = 38 kg/m².

Let's sum up all the loads → wind + snow + roofing = 13 + 103 + 38 = 154 kg/m² +10% safety factor ≈ 170 kg/m².

The total load on the roof must be at least 200 kg/m².

In our example, the total load was less. In this situation, for further calculations, the minimum permissible value should be taken as a basis, that is, 200 kg/m².

To determine the pressure on the Mauerlat, it is necessary to add the weight of the rafters (≈ 20 kg/m²) to the total loads, which will be 220 kg/m².

Calculation of the cross-section of lumber and the length of rafters

After determining the total load, we select the required section of wood, for which the first step is to calculate the length of the rafter legs. Let's look at the sketch. The rafters of a sloping roof consist of two parts - before the break and after it. We calculate both parts separately, using the Pythagorean theorem in both cases:

Table: relationship between load and beam thickness

After calculations, we select the width of the board according to the specifications of manufactured lumber, focusing on the bottom plate.

Table: softwood lumber (section according to GOST 24454–80)

Board thickness, mm	Board width, mm
16	75	100	125	150	-	-	-	-	-
19	75	100	125	150	175	-	-	-	-
22	75	100	125	150	175	200	225	-	-
25	75	100	125	150	175	200	225	250	275
32	75	100	125	150	175	200	225	250	275
40	75	100	125	150	175	200	225	250	275
44	75	100	125	150	175	200	225	250	275
50	75	100	125	150	175	200	225	250	275
60	75	100	125	150	175	200	225	250	275
75	75	100	125	150	175	200	225	250	275
100	-	100	125	150	175	200	225	250	275
125	-	-	125	150	175	200	225	250	-
150	-	-	-	150	175	200	225	250	-
175	-	-	-	-	175	200	225	250	-
200	-	-	-	-	-	200	225	250	-
250	-	-	-	-	-	-	-	250	-

As you can see, for a 40 mm thick board there is a wide range of choices. In order not to overpay, but at the same time provide the rafters with sufficient strength, there are formulas in which, with a known thickness of the beam, you need to substitute the corresponding width of the board one by one, starting with the smaller value:

• α < 30° - H ≥ 8,6 х L max х √Q r: (B х R изг);
• α > 30° - H ≥ 9.5 x L max x √Q r: (B x R bend).

Wherein:

Video: what to consider when choosing lumber

We carry out calculations and strength tests:

1. Determine the width of the lower rafters. Since the lower angle of inclination is 47°, we will use the second formula, substituting tabular and calculated parameters into it → H ≥ 9.5 x L max x √Q r: (B x R bend) = 9.5 x 2.543 x √160: ( 4 x 140) = 12.8 cm, that is, H ≥ 12.8 cm = 15 cm (the nearest larger value according to the table).
2. We check the correctness of the calculations, for which the inequality must be observed [(3.125 x Qr x Lmax³) : (B x H³)] ≤ 1 = [(3.125 x 160 x 2.543³) : (4 x 15³)] ≤ 1 = 0.61 ≤ 1, that is, the inequality is maintained and the section of 40x150 mm for the lower rafters is selected correctly.
3. Similarly, we determine the width of the upper rafters using the same formula, since the bend angle is 32° → 9.5 x 2.414 x √160: (4 x 140) ≥ 12.15 cm = 12.5 cm (closest values).
4. We check by substituting the result → [(3.125 x 160 x 2.414³) : (4 x 12.5³)] ≤ 1 = 0.9 ≤ 1.
5. To summarize, a 40x150 mm board is suitable for the lower rafters with a good margin of safety, and 40x125 mm for the upper rafters with a small margin.

The basic rule of construction is to make all roundings upward in any calculations. The same applies to tabular and standard values.

Mauerlat calculation

There are no requirements for the cross-section of timber for floors and mauerlat in the standards, so you should refer to the table, adjusting its values ​​for the design load.

Table: ratio of thickness and length of timber for mauerlat and floors

The load on the Mauerlat, according to our calculated values, is 220 kg/m², therefore, 220/400 = 0.55. We multiply this index by the table value close to the pitch of the rafters and the length of our span - 150x250 mm - 0.55 x 150 and 0.55 x 250 = 82.5x137.5 = 100x150 mm.

Video: choosing wood, how to make a profit on the cross-section

Calculation of the pitch and number of rafter legs

The pitch of the rafters must be calculated and not taken at random, since this indicator affects the design of the roofing pie, contributes to savings during construction, and also ensures the durability and reliability of the entire roofing system:

1. We calculate the number of rafter legs → wall length: recommended step +1 = 8.8/0.8 + 1 = 12 pieces on one side.
2. We calculate the pitch → length of the house: number of rafters = 8.8/12 = 0.73 ≈ 0.8 m. We adopted this step initially, so there is no need to adjust it.

Video: pitch of rafters for various roofs

Let's summarize the calculations - to build a load-bearing frame for a sloping mansard roof according to our example, you will need:

• 62 linear m boards Ø40X150 mm (24 lower rafters 2543 mm long);
• 60 linear m boards Ø40Х125 mm (24 upper rafters 2414 mm long);
• 29 linear m of timber Ø100X150 mm for the Mauerlat laid around the perimeter;
• 80 linear m of timber Ø100X150 mm for floor beams installed in increments of 0.8 m - when calculating, take into account that the interfloor floor must withstand a load of up to 400 kg/m², taking into account the weight of the beams themselves, in addition, try to lay the beams rationally - the shorter they are, the smaller the cross-section required;
• 27 linear m of timber Ø100Х150 mm for vertical posts;
• 49 linear m of timber Ø100X150 mm for the upper floor beams - permissible load for the upper (attic) floor - 200 kg/m².

For each item, you should add 5–10%, which will be used for arranging tie rods, headstocks, lengthening rafters if necessary, or replacing defective wood.

The calculation of the rafter system for an attic roof is simple, just voluminous, but it is advisable to understand it, especially since it is presented consistently and as completely as possible.

Video: simplified calculation of the rafter system

Installation of a broken rafter system

Installation of the supporting structure begins with preparation for the construction of the roof, which includes the following work:

• purchase of lumber according to calculations, their sorting and treatment with antiseptics;
• checking the availability and serviceability of all working tools;
• clearing the work area of ​​excess debris;
• installation of scaffolding, bridges and ladders;
• checking the geometry of the base by measuring the box diagonally (deviation of no more than 20 mm is permissible), as well as the height of the walls along the entire perimeter of the house relative to the ground surface;
• Preparation of purlins, crossbars, struts and a template for creating roof trusses.

Video: installation of a gable mansard roof rafter system, part 1

Installation is carried out in the following order:

1. Installation of the Mauerlat. To increase the rigidity of the structure, professionals advise installing an armored belt under the Mauerlat, into which anchors or studs are poured in increments of no more than 2 m. Lay two layers of roofing felt or roofing felt, which will serve as waterproofing and protect the Mauerlat from getting wet and rotting. A beam is laid on top of the roofing felt and secured with anchors, studs or staples (for brick or block walls). In wooden or frame buildings, the last crown or beam serves as the mauerlat.

   The longevity and operational efficiency of any roof largely depends on the quality of installation and the strength of the Mauerlat fastening

2. Installation of floor beams. They are laid on top of the Mauerlat or in pre-arranged wall pockets with a pitch selected for the rafters. With a large rafter pitch, floor beams can be installed more often (optimally every 60 cm, so that later the tile insulation can be laid without trimming), although this will entail an increase in lumber.

   Before making a wooden floor, it is necessary to make a full calculation of the expected loads, purchase the necessary material and tools

3. Installation of the rafter frame. Vertical posts are installed on the laid floor beams, forming an attic. The attic floor beams are laid on top of them and the racks are connected with longitudinal girders. Headstocks are mounted in the center of the racks and a ridge run is laid. For leveling, use a level or a bright cord stretched between the outer posts.
4. Installation of rafters. They start with the installation of layered rafters. First of all, a template is made from a rejected board according to the calculated dimensions. Apply it to the mauerlat and purlin, mark the shape of the cut and cut it out. All lower rafter pairs are made using the finished stencil. They are leveled and, if necessary, reinforced with struts. A stencil for the upper rafters is made in the same way, applying it to the purlins and cutting out the edges according to measurements. Hanging rafters are fastened together on a ridge beam end-to-end or overlapping using metal plates, wooden plates, bolts, etc.

   The frame of the future attic can be made and installed independently, observing the technological features of roofs of different configurations

Video: installation of a gable mansard roof rafter system, part 2

Installation of main components

The main components of the attic structure are:

• ridge knot;
• “post-strut-rafter” assembly;
• “beam-post-struts” assembly;
• and others, depending on the type of structure chosen and the presence of crossbars, tie-rods, etc.

Installation of roofing units, methods of fastening, the possibility of horizontal shift, etc. is a separate big topic, therefore, within the framework of this article, we will consider the formation of some as an example.

Ridge knot

To ensure greater structural strength, especially with a low slope of the slopes, a durable ridge girder is installed so that it can take on part of the loads exerted on the rafters. Then proceed as follows:

Attaching the rafters to the mauerlat

In order for the fastening of rafters to the supporting base (mauerlat, floor beams or wall) to be reliable, it is necessary to take into account statistical and dynamic loads, as well as the coefficient of linear expansion. Previously, rafters were fastened using the cutting method, which formed a strong unit, but increased wood consumption. Notches are still used today on large-section wooden structures.

But more often, in order not to weaken the structure, the rafters are fixed to the support by sawing or “tenon and groove”, by sewing a thrust beam or by cutting out grooves in the mauerlat. Galvanized corners, nails, staples, and dowels are used as fasteners. Such fastenings are rigid and not always practical.

Rigid fastening of the rafters to the Mauerlat guarantees the absence of any displacement of all key elements

In some cases, the rafters must be able to move horizontally (mainly in wooden houses, since wood is subject to temperature and humidity deformations, and this can cause the walls to warp), which is achieved using sliding supports. Such supports consist of a guide strip fixed to the rafters and an angle with a support platform, fixed to the mauerlat or the upper crown of the log house.

The choice of sliding rafters is justified only when there is a ridge beam against which they could rest with their upper part

Video: attaching rafters to the supporting base

https://youtube.com/watch?v=WKsOgTaVVQY

Attaching rafters to the floor beam

In this unit, it is important to avoid sliding of the rafters in order to prevent the destruction of the roof, for which the following connections are used:

• emphasis at the end of the beam;
• tooth with a spike;
• tooth with emphasis.

All elements are connected with screws, bolts, angles, nails, triangular plates, and tenons.

Rafters are connected to floor beams only when they know for sure that they will withstand the pressure applied

Video: how to install rafters evenly and in the same plane

An attic may have an unusual shape, a beautiful covering, and be made of the most modern materials, but if the supporting frame is not made correctly, then all the attractiveness of the attic will be reduced to zero. And along with it, the reliability and durability of the roofing structure, which will undoubtedly affect the comfort and coziness of the house. Therefore, knowing the principles of the rafter system of a mansard roof and correctly calculating its main elements is the developer’s primary task. Good luck to you.

A house with an attic is not only an additional living space, but also a respectable appearance for the entire building. Even if the room under the roof is made unheated and is used only in the summer, it still creates a powerful “air cushion” that helps retain heat inside the entire building.

And about that - read on our portal.

Attic project

When drawing up a diagram for the construction of an attic, it is best to do this in different projections in order to see and understand the placement of all elements of the rafter system. It is very important to correctly calculate the height of the roof ridge, since the size of the area under it will directly depend on it.

When drawing up a design diagram for the construction of an attic roof, you need to calculate the height of the ridge, ceiling and total area of ​​the room.

The minimum height from the floor to the ridge should be 2.5-2.7 m, but if this distance is less, then the room is not an attic, it can only be called an attic. This parameter is established by SNIP standards.

In order for all the elements to be drawn accurately and have the desired location in the overall system, you need to start from a figure with right angles, that is, a rectangle or square - a section of the attic room being created. Based on the sides (height and width of the future room), it will be almost impossible to make a mistake with the magnitude of the angles at which the roof slopes are located, with the location of the ridge, rafters and all supporting elements. When determining these parameters, they must immediately be entered into the drawing.

First you need to find the middle of the width of the front wall. Starting from this point, the parameters of the height of the ridge, the future ceiling of the attic, the location of the wall studs and the size of the eaves overhang are determined.

Due to the fact that each of the structures has a certain number of connecting nodes, which have different configurations, it would be a good idea to draw each of these connections separately in order to understand their features of interconnecting all the elements connecting at this point.

Any rafter system consists of basic elements and additional ones, which may not be present in every structure. The main components of an attic roof include:

• Floor beams, which are the basis for the remaining elements of the rafter system. They are laid on the main walls of the building.
• A rafter leg, straight in a gable roof system or consisting of two sections - in a broken pattern. In this case, the top rafter is called the ridge rafter, since it forms the highest point of the roof - and the rafters that form the walls of the attic are called side rafters.
• A ridge board or beam is a mandatory element for a gable roof, but is not always used when installing a broken roof model.
• Mauerlat is a powerful beam attached to the main side walls of the building. Rafter legs are installed on this element.
• Racks are the supporting elements necessary to strengthen a gable and broken structure. In the latter case, the ridge and side rafters are attached to it, and in the first, the stand is a reliable support for a long rafter. In addition, the racks serve as a frame for insulating and covering the walls of the attic.
• Diagonal bracing members or bevels additionally secure posts or longitudinal beams and rafters, making the structure more durable.
• Attic floor beams are used in all attic options - they connect the racks, and they also serve as the frame for the ceiling.
• Inter-rafter purlins are installed in a broken roof for structural rigidity.

To be sure that the prepared project is developed correctly, you need to show it to a specialist. Only he will be able to determine whether the attic parameters are correctly selected for the width and length of the walls of the building.

Video: professional calculation of a mansard roof using special software

Material parameters for the construction of an attic roof

If the graphic design is ready, then, based on the dimensions marked on it, you can calculate the amount of materials required for the construction of the attic roof. Materials must be selected according to their characteristics, which must meet fire and environmental safety requirements. For wood, it is necessary to provide special treatment with fire retardants, which will reduce the flammability of the material. So, for construction you will need:

• Boards for rafter legs. Their cross section is selected based on the results of special calculations - this will be discussed in more detail below.
• A beam having a cross-section of 100×150 or 150×200 mm is for floor beams, depending on the chosen rafter system and the width between the load-bearing walls, as well as for purlins, diagonal legs or valleys - if they are provided for in the design.
• Beam with a cross section of 100×150 mm or 150×150 mm for laying the Mauerlat.
• For racks, timber 100 × 100 or 150 × 150 mm is usually used.
• Unedged board for laying the subfloor and some fasteners.
• Annealed steel wire with a diameter of 3-4 mm - for fastening some parts together.
• Nails, bolts, staples of various sizes, angles of various configurations and other fasteners.
• A metal sheet with a thickness of at least 1 mm is for cutting out overlays.
• Lumber for sheathing and counter-lattens for roofing material - depending on the type of roof chosen.
• – for thermal insulation of the roof.
• Waterproofing and vapor barrier membranes.
• Roofing material and fastening elements for it.

What section of rafters are required?

Rafters are roofing elements that will bear the main external loads, so the requirements for their cross-section are quite special.

The size of the required lumber will depend on many parameters - on the step between the rafter legs, on the length of these legs between the support points, on the snow and wind load that falls on them.

The geometric parameters of the rafter system design are easy to determine in the drawing. But with the remaining parameters, you will have to refer to the reference material and make some calculations.

Snow load is not the same for different regions of our country. The figure below shows a map on which the entire territory of Russia is divided into zones according to the intensity of the snow load.

There are eight such zones in total (the last, eighth, is rather extreme and can not be considered for the construction of an attic roof).

Now you can accurately determine the snow load, which will depend on the angle of the roof slope. For this there is the following formula:

S = Sg × μ

Sg– table value – see the map and the table attached to it

μ — correction factor depending on the steepness of the roof slope.

• If the slope angle is me 25°, then μ=1.0
• With a slope from 25 to 60° - μ=0.7
• If the roof is steeper than 60°, then it is considered that snow does not linger on it, and the snow load is not taken into account at all.

It is typical that if the attic roof has a broken structure, then for different sections of it the load can have different values.

The slope angle of the roof can always be determined either with a protractor - according to the drawing, or by a simple ratio of the height and base of the triangle (usually half the span width):

Wind load also mainly depends on the region in which the building was built and on the characteristics of its surroundings and the height of the roof.

And again, for the calculation, the initial data on the map and the table attached to it are first determined:

The calculation for a specific building will be carried out according to the formula:

Wp = W × k × c

W– table value, depending on the region

k– coefficient taking into account the height of the building and its location (see table)

The following zones are indicated by letters in the table:

• zone A - open areas, steppes, forest-steppes, deserts, tundra or forest-tundra, windswept sea coasts, large lakes and reservoirs.
• zone B – urban areas, wooded areas, areas with frequent wind obstacles, relief or artificial, at least 10 meters high.
• zone IN– dense urban development with an average building height above 25 meters.

With– coefficient depending on the predominant wind direction (wind rose of the region) and on the angle of inclination of the roof slopes.

With this coefficient the situation is somewhat more complicated, since the wind can have a dual effect on the roof slopes. So, it has a direct, overturning effect directly on the roof slopes. But at small angles, the aerodynamic effect of the wind takes on special importance - it tries to raise the slope plane due to the resulting lift forces.

The drawings, diagrams and tables attached to them indicate areas of the roof exposed to maximum wind loads, and indicate the corresponding coefficients for calculation.

It is characteristic that at slope angles of up to 30 degrees (and this is quite possible in the area of ​​ridge rafters), the coefficients are indicated both with a plus sign and negative, that is, directed upward. They somewhat dampen the frontal wind load (this is taken into account in calculations), and in order to neutralize the effect of lifting forces, it will be necessary to very carefully secure the rafter system and roofing material in this area, using additional connections, for example, using annealed steel wire.

Once the wind and snow loads have been calculated, they can be summed up and, taking into account the design features of the system being created, the cross-section of the rafter boards can be determined.

Please note that the data is given for the most commonly used coniferous material (pine, spruce, cedar or larch). The table shows the maximum length of the rafters between the support points, the section of the board depending on the grade of the material, and on the pitch between the rafters.

The value of the total load is indicated in kPa (Kilopascals). Converting this value into more familiar kilograms per square meter is not difficult. With quite acceptable rounding we can accept: 1 kPa ≈ 100 kg/m².

The dimensions of the board along its cross-section are rounded up to standard lumber sizes.

	rafter section (mm)	Distance between adjacent rafters (mm)
		300	600	900	300	600	900
		1.0 kPa			1.5 kPa
higher	40×89	3.22	2.92	2.55	2.81	2.55	2.23
	40×140	5.06	4.60	4.02	4.42	4.02	3.54
	50×184	6.65	6.05	5.28	5.81	5.28	4.61
	50×235	8.50	7.72	6.74	7.42	6.74	5.89
	50×286	10.34	9.40	8.21	9.03	8.21	7.17
1 or 2	40×89	3.11	2.83	2.47	2.72	2.47	2.16
	40×140	4.90	4.45	3.89	4.28	3.89	3.40
	50×184	6.44	5.85	5.11	5.62	5.11	4.41
	50×235	8.22	7.47	6.50	7.18	6.52	5.39
	50×286	10.00	9.06	7.40	8.74	7.66	6.25
3	40×89	3.06	2.78	2.31	2.67	2.39	1.95
	40×140	4.67	4.04	3.30	3.95	3.42	2.79
	50×184	5.68	4.92	4.02	4.80	4.16	3.40
	50×235	6.95	6.02	4.91	5.87	5.08	4.15
	50×286	8.06	6.98	6.70	6.81	5.90	4.82
total snow and wind load		2.0 kPa			2.5 kPa
higher	40×89	4.02	3.65	3.19	3.73	3.39	2.96
	40×140	5.28	4.80	4.19	4.90	4.45	3.89
	50×184	6.74	6.13	5.35	6.26	5.69	4.97
	50×235	8.21	7.46	6.52	7.62	6.92	5.90
	50×286	2.47	2.24	1.96	2.29	2.08	1.82
1 or 2	40×89	3.89	3.53	3.08	3.61	3.28	2.86
	40×140	5.11	4.64	3.89	4.74	4.31	3.52
	50×184	6.52	5.82	4.75	6.06	5.27	4.30
	50×235	7.80	6.76	5.52	7.06	6.11	4.99
	50×286	2.43	2.11	1.72	2.21	1.91	1.56
3	40×89	3.48	3.01	2.46	3.15	2.73	2.23
	40×140	4.23	3.67	2.99	3.83	3.32	2.71
	50×184	5.18	4.48	3.66	4.68	4.06	3.31
	50×235	6.01	5.20	4.25	5.43	4.71	3.84
	50×286	6.52	5.82	4.75	6.06	5.27	4.30

Tools

Naturally, during work you cannot do without tools, the list of which includes:

• Electric drill, screwdriver.
• Building level and plumb line, tape measure, square.
• Axe, chisel, chisel, hammer
• Circular saw, jigsaw, hacksaw.
• Carpenter's knife.

Installation will be accelerated if the tools for the work are of high quality, and the work will be carried out with competent mentors and assistants, carefully and step by step.

Installation stages

It is necessary to strictly follow the sequence of work - only under this condition the structure will be reliable and durable.

Mounting the Mauerlat

Installation of any rafter system begins with securing a powerful supporting structure to the end of the side walls of the building. timber - mauerlat, on which it will be convenient to install rafter legs. The Mauerlat is made from high-quality timber with a cross-section of at least 100 × 150 mm. It must be laid on roofing felt waterproofing laid along the upper end of the wall (regardless of the material).

Due to the Mauerlat, the load will be evenly distributed over the walls and transferred to the foundation of the building.

The Mauerlat is secured to the wall using metal pins, which are pre-embedded in a concrete belt or crown running along the upper edge of the wall, or with anchor bolts with a diameter of 12 mm. They must go into the wall at least 150 — 170 mm. If the Mauerlat is installed on a wooden wall, then the beams are attached to it using wooden dowels.

Installation of truss structure

• Installation of the rafter system begins with the installation of floor beams. They can be attached to the mauerlat from above if the beams are planned to be moved outside the perimeter of the building and thereby increase the area of ​​the attic. In this design, the rafter legs are fixed to the floor beams.

Floor beams fixed on top of the Mauerlat (Fig. A)

• In another case, they can be stacked on waterproofed walls and fastened with corners or brackets to the inner edge of the Mauerlat. This option is used when the rafter legs are planned to be attached directly to the mauerlat.

Another option is that only the rafter legs are attached to the Mauerlat

• Next, you need to find the middle of the floor beam, since this mark will become a guideline for determining the location of the support posts and the ridge.
• The racks should be located at the same distance from the marked middle of the floor beam. They will subsequently determine the location of the walls of the attic room, that is, its width.
• The bars for the racks must have a cross-section equal to the size of the floor beams. The constructions are attached to the beams using special corners and wooden overlays. However, to begin with, they are first nailed, then carefully leveled using a building level and a plumb line, and only then are they permanently secured, taking into account future loads.

• When the first pair of racks is installed, they are fastened together from above with a bar, which is called a tie. This tightening is also connected to the racks using special metal corners.

• After securing the tie, you will get a U-shaped structure. Layered rafters are installed on its sides, the second end of which is attached to the floor beam or placed on the mauerlat.
• A special recess (groove) is cut into the installed supports for the timber or in the rafters. With its use The rafters are tightly installed on the Mauerlat beam and secured with metal brackets.

• To provide rigidity to the structure, additional struts can be installed from the base of the rack to the middle of the installed side rafters. If this does not seem enough, and saving material is not in the foreground, then you can strengthen the overall structure with additional racks and contractions (they are indicated in the drawing, Fig. A, with translucent lines).
• Next, while tightening, the middle is calculated - the headstock will be attached to this place, supporting the ridge connection of the upper hanging subsystem of the rafters.
• The next step is to install the ridge rafters, which can be fastened together with various connections - this can be a metal plate or powerful bolts with metal plates or washers.

• After installing them, the headstock is attached to the ridge and the middle of the tightening.
• Having completed work on one part of the rafter system, you need to make all the rest according to the same principle. The distance between adjacent rafters in such a system should be no more than 900 — 950 mm, but the optimal interval would probably still be 600 mm - this will provide the necessary rigidity and stability of the structure, and will be convenient for insulation using standard mineral wool mats. True, this makes the structure heavier and will require more materials.

• First, the side parts of the system assembly are installed, and then the intermediate parts. They are connected to each other by purlins, which are installed between the upper ends of the racks and act as spacers. Thus, you will get a rigid structure of the attic rafters, in which the frame for wall cladding will already be ready.

Prices for various types of fasteners for rafters

Rafter fasteners

Waterproofing attic roof

When the rafter system is built, you can proceed to finishing it and accompanying materials.

• The first coating that should be fixed directly on top of the rafters will be a waterproofing and windproof film. — it is attached to the rafters using staples and a stapler, starting from the cornice. The canvases are laid with an overlap of 150
• 200 mm, and then the joints are glued together with waterproof tape. — On top of the waterproofing, a counter-lattice is placed on the rafters, which will more reliably fix the film on the surface and create the necessary ventilation distance between the windproof and roofing material. The counter-lattice is usually made of boards 100 wide — 150 mm and thickness 50

• 70 mm.
• The sheathing is fixed perpendicular to the counter-lattice, on which the roofing material will then be laid. The pitch between the slats must be calculated depending on the type and size of the sheet roofing material, taking into account the overlap required for it

If a soft roof is chosen, then plywood sheets are most often attached to the counter-lattice.

Roofing installation

The roofing material is attached to the prepared sheathing or plywood. Its installation usually starts from the roof eaves and proceeds in rows, from one of the edges - depending on the type of roof. Roofing sheets are mounted with an overlap. If a metal profile or metal tile is used for the coating, then such material is secured with special self-tapping screws with elastic gaskets. Fastening elements are usually matched in color to the roofing material.

In addition, if a chimney pipe goes onto the roof, it requires a separate design of the hole inside the rafter system and an insulating layer, and on the roof, reliable waterproofing must be installed around the pipe.

You can find out in detail how and what is the best way to cover a roof on our portal; there is a whole section where you can find answers to many questions, including recommendations for reliable insulation of an attic room.

Prices for popular types of corrugated sheets

Corrugated sheet

Video: detailed video tutorial on building a mansard roof

It should be noted that the work of constructing any roof, and especially one as complex as an attic roof, is not only responsible, but also quite dangerous and requires special, increased safety measures. If you have no experience in carrying out such construction processes, then it is better to entrust their implementation to professionals or perform all actions under the supervision of an experienced craftsman, and with the utmost care and precision.

The rafter system is one of the final stages of building a house. The durability of the building itself and the comfort of living in it depend on how correctly it is executed. Simplicity of execution allows you to do the work yourself with the assistance of an assistant.

Rafter systems for the attic

Today there is a real boom in the use of various architectural elements in suburban construction, which, in the context of industrial construction, would seem to be a thing of the past forever. We are talking about devices such as bay windows, attics, mezzanines and the like. They can significantly increase the usable space and give the building an original, beautiful look.

Attics are especially popular, allowing you to create a full-fledged living space in the under-roof space. For this purpose, special rafter systems are used to ensure the possibility of creating such a room, provided that the structure is of sufficient strength.

The installation of a broken attic roof allows you to get a full-fledged living space on the second floor

Types of rafter systems

The main types of rafter systems for attic construction are presented in two options:

• gable;
• broken rafter system.

Photo gallery: what is an attic

A sloping roof allows you to obtain the optimal combination of the roof slope and the usable area underneath. It is possible to increase the volume of the attic in a structure under a gable roof only due to the high height of the ridge. The attic can be “equipped” with an external structure with a balcony under a separate roof. The balcony can be an integral part of the attic roof structure.

However, in practice, the roofs of a country house are so diverse that it is almost impossible to classify them. The design uses a variety of elements:

• hip bevels;
• birdhouses;
• awnings;
• semi-built-in translucent structures (greenhouses);
• lanterns and other architectural solutions in the most original and sometimes unexpected combinations.

Photo gallery: projects of houses with a gable roof and an attic

A gable roof can be decorated with an elegant “birdhouse”, which will also increase the area of ​​the attic. In large houses, a gable structure can be used as one of the elements of the roof composition. The main idea of ​​such a house is to combine simplicity of execution with perfectly selected finishing elements

Elements and components of the attic roof rafter system

Obviously, the most durable structure is a gable roof. But to obtain a sufficiently spacious room with such a rafter arrangement, it is necessary to reduce the angle between the slopes, and this leads to an increase in wind loads on the roof. A reasonable solution is to create a semi-attic, when racks are installed from floor to ceiling to a height of 1.3–1.8 meters, and rafters are already attached to them. Such a device requires the installation of low crossbars to compensate for the thrusting loads from the rafter legs on the racks.

To increase the useful volume of the attic, the crossbars that form its ceiling are installed as close as possible to the ridge unit

The use of a sloping roof allows you to simplify the shape of the attic room and obtain a larger volume of living space.

The construction of a sloping roof allows you to get a much larger attic than the installation of a conventional gable roof

The main elements of the rafter system are:

When installing a rafter system, additional parts are widely used to strengthen the fastening of structural elements.

The use of modern fasteners allows us to effectively strengthen the structure and significantly reduce installation time

Calculation of the rafter system

The initial data for the calculation are taken from a previously developed project. As an example, let’s look at a roofing diagram with an attic.

The design drawing indicates the dimensions, installation locations and material of all elements of the roofing system

The main indicator, calculated first of all, is the pitch of the rafters, depending on the planned finishing coating. So, to install ceramic tiles, the pitch of the rafters should be no more than 60 centimeters, and if you plan to install a plastic covering or soft roof, this figure can be increased to 120–150 centimeters. Again, you need to take into account the nature of the loads - a combination of the effects of wind and snow - and set the optimal angle between the roof slopes.

The procedure for calculating the number of rafters

For example, consider the installation of roofs for a house 10 meters long. As a first approximation, we take the distance between the rafter legs to be 80 centimeters. Then you will need them: 1000: 80 + 1 = 13.5. Since the number of rafters must be an integer, we round the result to 13. In this case, the exact distance between them will be 1000: 13 = 769 (millimeters). This is the exact value of the gap between the axes of the rafter legs.

When calculating the need for materials, you need to take into account their cutting ability. In the case of wood materials, their length can be 4 or 6 meters. During the design process, it is necessary to select the dimensions of parts taking into account the formation of the smallest amount of trim . Coniferous wood trimmings are unsuitable even for firewood for stoves.

Materials for truss structure

The traditional material for rafters in Russia is wood. Larch is considered the best option, however, due to price and availability, it cannot always be used. Therefore, beams made of coniferous wood are used. The size of the section depends on the design of the building.

Composite profiled wood materials are becoming increasingly common. These include:

1. Wooden I-beams. These products are interesting because they are made mainly from wood waste. The supporting surfaces are made of multi-layer waterproof plywood and the wall is made of OSB. Such structural materials have a load-bearing capacity no less than solid timber. The requirements for antibacterial fire protection treatment are much more relaxed; the material has already undergone all protective treatments during the production process. At the same time, it does not undergo cracking, and its mechanical properties are the same in all directions.

   In individual construction, wooden materials that mimic the shape of metal ones are increasingly being used.

2. Wooden channels. They are produced in the same way as I-beams. The main application is load-bearing elements of wooden structures. The strength characteristics of this profile are higher than those of natural wood and wooden I-beams. Often such products are made from solid coniferous wood. This significantly reduces the weight of the structures and the load on the foundation.

   A wood channel is stronger than timber and weighs less

3. Glued beam. This material is rarely used for the installation of rafter frames. Its main application is the laying of log houses. They use timber with a core made of ordinary pine needles and outer plates made of expensive wood species: oak, larch and other valuable materials. For rafters, beams made of homogeneous plates of increased length are used in highly stressed areas of the system.
4. Metal profiles. They are not used so often for assembling rafter frames. The most convenient material for installation is profile pipe. The disadvantage of metal profiles is the need for periodic measures to protect against corrosion. Elements of the rafter system, as a rule, are tightly closed by the roofing pie and the interior decoration of the attic, which greatly complicates access for maintenance.

   The metal truss structure is susceptible to corrosion and requires regular maintenance

Construction of a rafter system for a gable roof with an attic

The gable roof rafter system is based on a triangle - the most rigid figure.

Only the main elements of the rafter system are listed. Additional parts can be used to increase the strength of the structure.

Installation of the roof truss system taking into account the formation of the attic

The rafter system of a gable roof can be formed in two ways:

1. Assembly of the main structure below, followed by lifting to the ceiling and installation on the mauerlat.
2. Installation of rafter legs in detail directly at the installation site.

The first option is a more productive and convenient way.

Assembling the roof trusses below

This work is done in the following order:

Video: assembling roof trusses “on the ground”

Installation of rafter elements

The rafters, as the main load-bearing element of the roof skeleton, must be securely connected to each other. Many different methods have been invented for this, including specific ones designed for certain types of buildings. The rafter system of a wooden house requires special attention. The beam is attached to the Mauerlat by a sliding device, and the ridge connection is made on a hinge. This is due to constant seasonal movements of the log house, which must be compensated.

Photo gallery: methods of connecting rafter legs

The rafter legs are attached to the mauerlat using metal corners. The rafters are connected at the ridge end-to-end or through a cut. The critical nodes of the rafters are connected using metal connecting plates. The rafter legs are connected using special hinge joints, ensuring freedom of movement of the structure during seasonal deformations of the building. The joint in the ridge can be reinforced with bolts.

Installation of support posts and purlins

This is a responsible operation, because at this stage the surface of the front finishing of the walls and ceiling of the attic is formed. Therefore, the execution procedure is the same as when installing rafters:

For the manufacture of all parts of the rafter system, timber of the same dimensions is used, usually measuring 50x150 or 40x150 millimeters.

Video: quick installation of the rafter system

Lathing

This is a mandatory element of the rafter system. In the case where a warm attic space is formed in the under-roof space, the sheathing is done twice:

1. External sheathing is used to secure the finishing roof covering. In addition, if each board is attached to the rafters with two nails, it serves as a fastening element of the frame. In addition, an insulating and moisture-proof roof pie is formed under the sheathing.
2. The internal sheathing serves as a frame for insulating the attic and installing the final finishing of walls and ceilings.

In addition, counter-battens are also installed, with the help of which the ventilation system of the under-roof space is organized.

The counter-lattice is placed parallel to the rafters and provides clearance for ventilation of the under-roof space

For sheathing, a board measuring 25x100 millimeters, edged or unedged, is used. Unedged boards must first be sanded. It is not recommended to use a board wider than the specified size. When warping, it can deform the finishing coating or damage the roofing pie.

The sheathing boards are fastened with nails at least 70 millimeters long and at least two nails for each intersection. This method increases the structure’s resistance to wind loads.

The spacing of the sheathing depends on the material of the finishing coating - for ceramic tiles and soft roofing it should be minimal (about five centimeters); for metal tiles or corrugated sheets, a distance between the boards of up to 70 centimeters is allowed.

A properly laid roofing pie must contain a ventilation gap between the insulation and the roofing material, which helps quickly remove moisture

Video: lathing the rafter system

Rafter finishing

After installation of all roof elements, the rafter system becomes practically inaccessible for inspection and maintenance. Therefore, before installing each part in place, it must be carefully treated with protective compounds. There are enough special products on the building materials market to protect wooden structures from damage by bacteria and rot, as well as various fire-fighting impregnations.

Before installing parts of the rafter system, they must be treated with special protective compounds.

It should be taken into account that carrying out protective operations on a finished structure is not always effective, since hidden surfaces remain untreated.

Any wood protection products are certified by government agencies, so when purchasing, you need to ask the seller for a certificate of conformity. It is issued by sanitary authorities and fire inspectors. First of all, the safety of the composition for humans and its compliance with the declared qualities are guaranteed.

Which of them to choose is decided by the consumer himself, depending on his financial capabilities. In principle, you can always run into a fake, but this will become clear only after many years of use.

Impregnations can be applied with a wide folded brush or roller, but a spray gun is often used.

Video: installation of a gable roof rafter system with an attic

A reliable roof largely determines the life cycle of a building. A properly installed roof ensures the comfort and cost of living in a home. In Russian conditions, when heating is needed most of the year, a properly installed insulated roof retains up to 30% of the heat. And high-quality insulation is possible only with a high-quality rafter system.

An attic in a house is always interesting, beautiful and profitable. However, not every master will undertake to do all the work independently. Reasons: ignorance of technological subtleties and the complex rafter system of the attic roof. But you can build an attic yourself, the main thing is a good design and a sober assessment of your own strengths and financial capabilities. And we will advise and tell you what types of rafters there are, and we will analyze the structure of the rafter system of the attic roof of various types.

The drafting must take into account all the nuances. If miscalculations are made, the developer runs the risk of ending up with something different from what was planned. The simpler the roof, the more convenient it is to make it yourself. Types of roofs are:

1. Gable, where the slopes descend on both sides;
2. A broken line, consisting of two or more slopes of different angles of inclination;
3. Hip with a triangular shape of slopes;
4. Semi-hip - end-type slopes are located approximately half the height distance;
5. Dome for polygonal or round buildings;
6. Vaulted - in cross-section, such a roof has the shape of an arc.

The attic roof is distinguished as ventilated and non-ventilated. The type is selected depending on the climatic characteristics of the region, for example, in areas with high rainfall it is better to build ventilated facilities.

Types of rafter systems

The rafter system of the attic roof is selected depending on the layout of the building and differs as follows:

1. Layered rafter system attics are installed when the load-bearing partition runs through the middle of the building. The design redistributes the weight load and is suitable for buildings where the distance between the external wall panels and the internal support system does not exceed 7 m.
2. Hanging rafter systems applicable in the absence of internal partitions and walls. Supported by a mauerlat and a ridge girder, they are suitable for buildings where the distance between the external walls and the structure does not exceed 14 m.
3. Combined rafters Attics are most often needed in buildings where columns are installed instead of partitions. It turns out that part of the rafter structure rests on columns, and part is made in a hanging version. The absence of auxiliary elements, reduced load on the foundation and no cluttering elements are the main advantages of the system, which is why this option is used most often.

Important! The types of rafter systems are selected at the design stage in order to correctly calculate the required strength of the foundation. In the case when the decision to build an attic arises at the final stage of construction, an accurate diagram of the truss system of the attic roof and a complete recalculation of the weight of the house taking into account new data will be required. The process cannot be neglected, especially in areas with weak soil. Otherwise, the end result will be that the house will quickly subside, and groundwater will render the foundation unusable in a short time.

Structural features of the rafter system

The main components are little different from a conventional gable roof:

• Mauerlat is the base of the roof that bears the weight.
• Rafters are elements of the system that form the inclination of the slopes. The top is fixed to the ridge, the bottom - to the mauerlat or stand.
• Post - an element that supports the ridge or back of the rafter leg.
• Struts are needed to strengthen and support the rafter legs. The strut has an oblique cut and serves to prevent the rafters from bending under the weight of the mass.
• Ties - a horizontal tie of a pair of rafters, placed in the upper or lower part.

Important! Rafter elements are often made from the highest grade wood. A timber with a moisture content of no more than 15-18% is purchased and pre-treated with anti-rotting compounds and antiprenes.

Assembly diagram of the rafter system for the attic

An attic rafter system is quite a troublesome task, so it is better to entrust the assembly to a specialist. But if this is not the case, tips and videos will help you complete the simplest design yourself.

1. The mauerlat beam is laid on the top frame of the walls. If the house is log, you can get by with upper crowns reinforced with brackets.
2. Install floor beams. Mounting on the mauerlat or protrusions of wall panels. The simplest fastening is without extension, supported on the walls, but with extension is when the beam is carried outside the perimeter of the house to create an overhang. In this case, the distance between the end of the beam and the wall panel should be at least 0.5-1.0 m.
3. Vertical racks are installed. To do this, determine the middle of the floor beam, then equal intervals are set aside from it - the distance should be equal to the width of the attic room.
4. The puffs are secured to the racks, and it turns out that each pair of racks looks like the letter “P”.
5. Installation of the lower rafter elements is carried out with fastening to the rack. Fasteners - self-tapping screws or nails, fasteners on the mauerlat in the form of a movable fastening slider, compensating for the shrinkage effects of the timber.
6. Installation of rafters for the upper part of the attic roof is carried out by connecting each pair with a metal plate or bar.
7. Final processing includes laying a waterproofing membrane and sheathing. The lathing for soft roofing material is solid, for profiled sheets and other hard materials it is sparse.

The proposed installation of the rafter system is the simplest. It is quite possible to equip such a structure with your own hands, you just need to make the correct calculations, the rafter system, drawings of the attic roof, and diagrams will help you complete the work without errors.

Rafters with extension behind the wall panel

This option is used when there is a small amount of internal space. You will have to rest the rafter leg on the upper floor beam. Mauerlat is not needed here, but reinforcing struts are required. To strengthen the base, you can fill in a reinforced concrete belt. Attaching the floor beams to the monolithic belt is done with anchors, into which support posts are inserted to the maximum thickness of the beam.

Important! The external structure forms a cornice: for wooden houses the width is from 0.5 m, for those made of concrete and stone – from 0.4 m.

Scheme of work:

1. Install the outermost floor beams that form the outline of the overhangs. The section of the beams is 150*200 mm.
2. The remaining beams are mounted along a cord stretched between the outer beams: the distance between them is equal to the pitch of the rafter legs. Insulated roofs require a rafter pitch of 0.6 m; if rafters are installed with the specified pitch, they can be made from timber with a section of 50*150 mm.
3. Having cut out the tenons, prepare the supports.
4. Install the corner posts and secure them with temporary supports.
5. Use a plumb line to determine the location of the support points of the beams and select holes for them.
6. Install row posts and a pair of load-bearing supports in the centers of the attic gable.
7. Lay purlins from 50*150 mm boards. Secure the purlins with corners.
8. Connect the supports with bars, also securing them with corners to the purlins.
9. Fasten the crossbars using temporary fasteners with an inch. The deviation from the edge of the frame is 300-350 mm.
10. Make a template for the bottom row of rafters: attach the blank board to the end of the purlin and beam, determine where to cut off the excess, try it on and trim it.
11. Install the end rafter supports.
12. Make a template for the top of the rafter legs.
13. Try on the template and build a tier, how the rafter system will be, photos of the attic roof will clearly show the entire structure.
14. If the templates fit perfectly, make the required number of rafter legs, mount them in place, strengthen the crossbars with the headstock to avoid their sagging and firmly sew them to the ridge area. The lower part does not require rigid hemming, it should be free.

The final completion is the installation of the gable frame, sheathing and roofing material. If it is not entirely clear how to complete this project, watch a video from professionals; the material will help you understand the intricacies of construction.

Attic from frame modules

The mansard roof rafter system involves a version of frame modules that is much simpler than the previous one. It is not groups of individual supports that are mounted on the ceiling, but ready-made block modules of the side walls of the future attic room. Such designs of mansard roofs and their rafter system allow you to work not at height, but below, calculating and measuring every step. The step-by-step process is as follows:

1. Make the walls of the attic according to the design in advance, with the longitudinal beams acting as purlins and support elements. Together with the racks, lay out these elements on a flat area and mark the sockets for the support points of the side walls with squares - make cuts along them.
2. Select a spike on the racks.
3. Connect the longitudinal beam with the vertical posts and you get a frame module (double). These are the future walls of the attic.
4. Lift the frames up and install them in place. Temporarily secure the installed frames with spacers and then fasten them with brackets.
5. Select sockets at the edges of the beams for mounting the lower row of rafters; if necessary, modify the sockets with a chisel.
6. The upper rafter tier is made on the ground, for which the blanks are first adjusted to the required elements.
7. The base of the upper triangle of the attic structure is a stretcher, and its length is equal to the distance between the installed planes (vertical) of the already mounted frames.
8. Select sockets along the edges of the stretch, and spikes on the lower heels.
9. Assemble rafters for the attic of the upper tier, mount a crossbar for additional fastening, and reinforce the ridge assembly with a triangular-shaped wooden overlay.
10. Pre-production of rafter legs for the attic will allow you to avoid working at height. You only need to cut the top bevel, which rests on the top post of the wall panel and on the tension of the upper trusses.
11. Try on the lower rafter part to the end, mark the tenon shape area on the lower heel, cut out the tenons according to the drawing made.

Now all that remains is to move upstairs and raise all the rafters. First install the trusses, securing them to the upper frame of the walls, and then install the lower part, attaching them to the ceilings (beams) with brackets. It turns out to be a completely comfortable floor, the rafter system for which was assembled on the ground. To make it easier to understand the task of building an attic roof, a modular rafter system, watch the video. All other stages are carried out according to the standard scheme of a conventional gable structure; the attic and rafter system are shown above.

An attic space equipped as an attic is one of the options for increasing the usable area of ​​the house. The roof of such a room must be strong, and its rafter system must be able to withstand heavy loads.

When constructing an attic, a rafter system is used, which differs in shape and type of construction. The roof can be:

1. Gable. The easiest way to install a structure is a symmetrical gable roof.

It has a frontal view in the shape of a triangle. If the width of the house does not exceed 6 meters, then the angle of inclination in such a roof can be within 45 degrees. If the house width is more than 6 meters, the angle should be increased to 60 degrees.

The advantage of such a mansard roof is the ease and speed of installation, the reliability of the structure and its ability to withstand significant loads.

The disadvantage is the small space inside the room, which does not allow you to design a large attic

Installation of a gable roof rafter system https://www.youtube.com/watch?v=3ykQjiMMUbA

1. Three-slope and four-slope. It has another name - asymmetrical, having slopes of different slopes and lengths.

The advantage of such a roof is its beautiful design and originality.

The disadvantage is that such a roof is much more expensive and has a complex shape that requires scrupulous calculations.

1. Broken gable. The slopes of such an attic structure have two parts located at different angles of inclination.

The advantage of a sloping roof is that in this option you can use the attic space as an attic with maximum efficiency. In addition, it is the most economical.

1. Half-hip. One of the types of gable roofing. A characteristic feature is two slopes (hip) above the front part of the roof.
2. Hip. It consists of trapezoidal slopes on both sides of the long roof and triangular slopes on both sides of the short one.

The advantage of half-hip and hip roofs is that, due to the absence of gables, they are able to bear significant loads. They have low windage. The rafter system of such roofs makes it possible to install an overhang of significant dimensions, which will serve as protection from atmospheric phenomena. more durable.

The disadvantage is the difficulty of installation. Hips reduce the overall space of the attic. Hip and half-hip roofs require windows, which must be given special attention at the design stage. Windows located in the slope itself are easier to manufacture and install, but must be closed during precipitation. Vertical window openings are much more convenient, but their equipment and installation are much more complicated.

Design of a rafter system for a hip roof

Material for the rafter system

The materials used for the manufacture of load-bearing structural elements must be durable, withstand temperature changes, have a low specific gravity and be resistant to moisture. The most suitable material is wood. Conifers with high strength and minimal rotting are chosen for the construction of the structure. These can be larch, pine or spruce. The finished timber must be treated with an antiseptic and fire-resistant material. Also, the roof rafter system can be made of laminated veneer lumber, but this will entail an increase in the length of the run.

The rafter system can be made of lightweight metal structures. This roof option is easy to install, easy to operate and maintain, but costs much more.

Main elements of the rafter system

The basis on which the internal and external cladding of the attic space is mounted is the rafter structure. There are often cases when the internal space between the roof and the cladding is used for laying various types of communications.

The structure consists of the following parts:

1. Rafters. They are one of the main elements of the frame of the entire structure. The angle of inclination of the slope, the design, stability and strength of the structure depend on their shape and quantity.
2. Runs. Designed for connecting rafters.
3. Mauerlat. Rafters are mounted on it. Serves as a foundation for the entire attic structure, evenly distributing the load on the building along its entire perimeter.
4. Lathing. Sheathing material mounted on the rafters to which the roof is attached. In addition, it increases the rigidity of the entire structure.
5. Horse. The place of the upper fastening of the attic roof slopes.
6. Support post, strut. Spacer elements that strengthen the rafters.
7. Sill. Beam between the front wall and the ceiling. Mounted parallel to the ridge. Serves as a basis for attaching struts and racks. Gives strength and stability to rafters.
8. Puff. A fastener designed to secure rafters.
9. Fillies. A piece of timber that extends the rafters to create the required length of roof overhang.
10. Roof overhang. The lower part of the roof that extends beyond the walls. Designed to protect walls and foundations from exposure to precipitation.

Broken attic structure and its calculation

The attic with a sloping roof is the most used, since the area under the roof can be used to maximum benefit. The reference diagram is considered to be a diagram in the cross-section of which there are elementary figures: a rectangle in the center, an equilateral triangle at the top, two right-angled triangles on the sides.

Drawings of this design are easy to calculate. The general diagram and individual drawings are drawn onto paper before starting calculations.

• A sloping roof is calculated using the following elements:
• calculation of the angle at which the roof will be installed;
• determining the dimensions of ridge and side rafters, as well as elements to strengthen them;
• calculating the dimensions of the sheathing;
• calculation of slope areas;
• determining the mass of materials needed for the roof;
• calculation of load and mass of insulation;

establishing the required distance between the rafters. Important!

The angle at which the roof is installed should be within 30 degrees in its upper part and 60 degrees for the side rafters.

The length of the side rafters is calculated using the formula. We have the initial data: 0.5 m – roof eaves, 2.5 m – support height, 60 degrees – inclination angle. We apply the formula for calculating the hypotenuse of a right triangle.

L = cornice + height / cosinus 60 = 0.5 + 2.5 / 0.5 = 5.5 meters.

The length for ridge rafters is calculated using the formula for an equilateral triangle. Let’s assume that the base or tie is 4 meters, the angles A at the base correspond to the angle of inclination of the ridge rafters, which is 30 degrees, at the top of the triangle the camber angle is 120 degrees.

L = puff / 2cosinus A = 4 / 2x0.86 = 2.3 meters.

The density and pitch of the sheathing depends on the roofing material. For a soft roof, plywood sheathing is installed over the entire surface of the rafters. For large semi-rigid and rigid roofs, compacted or thin sheathing is installed. Under a large semi-rigid roof it is necessary to lay a continuous layer of sheathing. Basically, the lathing is installed every 25-35 cm. The width of the board is about 25 cm.

To calculate the area, the structure is divided into geometric shapes. Their areas are calculated separately each, then all data is summed up. For a broken attic structure, the area is divided into 4 parts: 2 side, 2 ridge. Calculate the area of ​​each, double it and then add everything up.

Calculating the weight of the roof is a mandatory element. Approximate weight 1 sq.m. roofing can be: slate - from 11 to 14 kg, soft tiles - from 9 to 16 kg, galvanized sheet - from 3 to 6 kg, ceramic tiles - from 50 to 70 kg.

The average load for a sloping roof should be at least 200 kg per linear meter. This will ensure that the snow load and wind are contained on the entire structure. In addition, there are correction coefficients that depend on the inclination of the structure: up to 25 degrees the coefficient is 1, from 25 to 60 degrees - 1.025, from 60 degrees and above - none.

The distance between the rafters is set differently, depending on the roof covering. If the rafters are made with a cross-section of 50x150 mm, then the approximate pitch between them can be:

• for ceramic tiles, slate, ondulin - 80 cm;
• for metal tiles – 60 cm;
• for corrugated sheeting – 90 cm.