Calculation of rafter spacing for various roofing materials. Distance between wooden rafters under metal tiles Pitch of the rafter system

A gable roof is formed on the basis of a frame that combines the simplicity of the device and unsurpassed reliability. But the roof skeleton of two rectangular slopes can boast of these advantages only if the rafter legs are carefully selected.

Parameters of the gable roof rafter system

You should start making calculations if you understand that the rafter system gable roof- this is a complex of triangles, the most rigid elements of the frame. They are assembled from boards, the size of which plays a special role.

Rafter length

Determine the length of strong boards for rafter system formula will helpa²+b²=c², derived by Pythagoras.

The length of the rafter can be found by knowing the width of the house and the height of the roof

The parameter “a” indicates the height and is independently selected. It depends on whether the under-roof space will be residential, and also has certain recommendations if an attic is planned.

Behind the letter "b" is the width of the building, divided in two. And “c” represents the hypotenuse of the triangle, that is, the length of the rafter legs.

Let’s assume that the width of half the house is three meters, and it was decided to make the roof two meters high. In this case, the length of the rafter legs will reach 3.6 m (c=√a²+b²=4+√9=√13≈3.6).

You should add 60–70 cm to the figure obtained from the Pythagorean formula. The extra centimeters will be needed to carry the rafter leg beyond the wall and make the necessary cuts.

The six-meter rafter is the longest, so it is suitable as a rafter leg

The maximum length of timber used as a rafter leg is 6 m. If a strong board is required longer length, then they resort to the fusion technique - nailing a section from another beam to the rafter leg.

Section of rafter legs

For various elements of the rafter system there are their own standard sizes:

• 10x10 or 15x15 cm - for mauerlat timber;
• 10x15 or 10x20 cm - for the rafter leg;
• 5x15 or 5x20 cm - for purlin and bracing;
• 10x10 or 10x15 cm - for a stand;
• 5x10 or 5x15 cm - for a bed;
• 2x10, 2.5x15 cm - for laths.

Thickness of each part load-bearing structure roofing is determined by the load that it will experience.

A beam with a section of 10x20 cm is ideal for creating a rafter leg

The cross-section of the rafter legs of a gable roof is affected by:

type construction raw materials, because the “aging” of logs, ordinary and laminated timber varies;

rafter leg length;

the type of wood from which the rafters were planed;

length of the gap between rafter legs.

The most significant effect on the cross-section of the rafter legs is the pitch of the rafters. An increase in the distance between the beams entails increased pressure on the supporting structure of the roof, and this obliges the builder to use thick rafters.

Table: rafter cross-section depending on length and pitch

Variable impact on the rafter system

The pressure on the rafter legs can be constant or variable.

From time to time and with varying intensity, the supporting structure of the roof is affected by wind, snow and precipitation. In general, the roof slope is comparable to a sail that is under pressure natural phenomena may tear.

The wind tends to overturn or lift the roof, so it is important to make all the calculations correctly

The variable wind load on the rafters is determined by the formula W = Wo × k x c, where W is the wind load indicator, Wo is the value of the wind load characteristic of a certain area of ​​Russia, k is a correction factor determined by the height of the structure and the nature of the terrain, and c is the aerodynamic factor coefficient.

The aerodynamic coefficient can vary from -1.8 to +0.8. A negative value is typical for a rising roof, while a positive value is typical for a roof on which the wind presses. At simplified calculation with a focus on improving strength, the aerodynamic coefficient is considered equal to 0.8.

Calculation of wind pressure on the roof is based on the location of the house

The standard value of wind pressure is determined from map 3 of Appendix 5 in SNiP 2.01.07–85 and a special table. The coefficient taking into account the change in wind pressure with height is also standardized.

Table: standard value of wind pressure

Table: k coefficient value

It's not just the terrain that affects wind loads. Great importance has a residential area. Behind a wall of tall buildings there is almost no threat to the house, but in an open space the wind can become a serious enemy for it.

The snow load on the rafter system is calculated using the formula S = Sg × µ, that is, the weight of the snow mass per 1 m² is multiplied by a correction factor, the value of which reflects the degree of roof slope.

The weight of the snow layer is indicated in SNiP “Rafter Systems” and is determined by the type of terrain where the building is built.

The snow load on the roof depends on where the house is located

The correction factor, if the roof slopes tilt less than 25°, is equal to one. And in the case of a roof slope of 25–60°, this figure decreases to 0.7.

When the roof is sloped more than 60 degrees, the snow load is discounted. Still, snow rolls off a steep roof quickly, without having time to negative influence to the rafters.

Constant loads

Loads acting continuously are considered to be weight roofing pie, including sheathing, insulation, films and finishing materials for furnishing the attic.

The roofing pie creates constant pressure on the rafters

The weight of the roof is the sum of the weight of all materials used in the construction of the roof. On average it is 40–45 kg/sq.m. According to the rules, 1 m² of rafter system should not have more than 50 kg of weight roofing materials.

To ensure that there is no doubt about the strength of the rafter system, it is worth adding 10% to the calculation of the load on the rafter legs.

Table: weight of roofing materials per 1 m²

Type of roofing finish	Weight in kg per 1 m²
Rolled bitumen-polymer sheet	4–8
Bitumen-polymer soft tiles	7–8
Ondulin	3–4
Metal tiles	4–6
Corrugated sheeting, seam roofing, galvanized metal sheets	4–6
Cement-sand tiles	40–50
Ceramic tiles	35–40
Slate	10–14
Slate roofing	40–50
Copper	8
Green roof	80–150
Rough flooring	18–20
Lathing	8–10
The rafter system itself	15–20

Number of beams

How many rafters will be needed to arrange the frame of a gable roof is determined by dividing the width of the roof by the pitch between the beams and adding one to the resulting value. It indicates an additional rafter that will need to be placed on the edge of the roof.

Let's say it was decided to leave 60 cm between the rafters, and the length of the roof is 6 m (600 cm). It turns out that 11 rafters are needed (including the additional timber).

Rafter system two pitched roof- this is a structure made of a certain number of rafters

The pitch of the beams of the supporting roof structure

To determine the distance between the beams of the supporting roof structure, you should pay close attention to such points as:

• weight of roofing materials;
• the length and thickness of the beam - the future rafter leg;
• degree of roof slope;
• level of wind and snow loads.

It is customary to place rafters at 90–100 cm intervals when choosing a lightweight roofing material

A normal step for rafter legs is 60–120 cm. The choice in favor of 60 or 80 cm is made in the case of constructing a roof inclined at 45˚. The same small step should be taken if you want to cover wooden frame roofs heavy materials like ceramic tiles, asbestos cement slate and cement-sand tiles.

Table: rafter pitch depending on length and cross-section

Formulas for calculating the rafter system of a gable roof

Calculation of the rafter system comes down to establishing the pressure on each beam and determining the optimal cross-section.

When calculating the rafter system of a gable roof, proceed as follows:

1. Using the formula Qr=AxQ they find out what the load on linear meter each rafter leg. Qr is the distributed load per linear meter of a rafter leg, expressed in kg/m, A is the distance between the rafters in meters, and Q is the total load in kg/m².
2. Proceed to determining the minimum cross-section of the rafter beam. To do this, study the data from the table included in GOST 24454–80 “Lumber coniferous species. Dimensions".
3. Based on standard parameters, choose the section width. And the section height is calculated using the formula H ≥ 8.6 Lmax sqrt(Qr/(BRbend)), if the roof slope is α< 30°, или формулу H ≥ 9,5·Lmax·sqrt(Qr/(B·Rизг)), когда уклон крыши α >30°. H is the section height in cm, Lmax is the working section of the rafter leg maximum length in meters, Qr - distributed load per linear meter of rafter leg in kg/m, B - section width cm, Rbend - bending resistance of wood, kg/cm². If the material is made from pine or spruce, then Ri can be equal to 140 kg/cm² (grade 1 wood), 130 kg/cm² (grade 2) or 85 kg/cm² (grade 3). Sqrt is the square root.
4. Check whether the deflection value complies with the standards. It should not be greater than the figure obtained by dividing L by 200. L refers to the length of the working section. Correspondence of the deflection value to the ratio L/200 is feasible only if the inequality 3.125·Qr·(Lmax)³/(B·H³) ≤ 1 is true. Qr denotes the distributed load per linear meter of the rafter leg (kg/m), Lmax is the working section of the rafter leg maximum length (m), B is the section width (cm), and H is the section height (cm).
5. When the above inequality is violated, the indicators B and H increase.

Table: nominal dimensions of thickness and width of lumber (mm)

Board thickness - section width (B)	Board width - section height (H)
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	-

Example of load-bearing structure calculation

Let us assume that α (roof inclination angle) = 36°, A (distance between rafters) = 0.8 m, and Lmax (working section of the rafter leg of maximum length) = 2.8 m. First grade pine material is used as beams , which means that Rben = 140 kg/cm².

Cement-sand tiles were chosen to cover the roof, and therefore the weight of the roof is 50 kg/m². Total load (Q) experienced by each square meter, equal to 303 kg/m². And for the construction of the rafter system, beams 5 cm thick are used.

The following computational steps follow from this:

1. Qr=A·Q= 0.8·303=242 kg/m - distributed load per linear meter of rafter beam.
2. H ≥ 9.5·Lmax·sqrt(Qr/B·Rben).
3. H ≥ 9.5 2.8 sqrt(242/5 140).
4. 3.125·Qr·(Lmax)³/B·H³ ≤ 1.
5. 3.125·242·(2.8)³ / 5·(17.5)³= 0.61.
6. H ≥ (approximate height of the rafter section).

In the table of standard sizes, you need to find a section height of the rafters that is close to 15.6 cm. A suitable parameter is 17.5 cm (with a section width of 5 cm).

This value fully corresponds to the deflection indicator in regulatory documents, and this is proven by the inequality 3.125·Qr·(Lmax)³/B·H³ ≤ 1. Substituting into it the values ​​(3.125·242·(2.8)³ / 5·(17, 5)³), we will find that 0.61< 1. Можно сделать вывод: сечение пиломатериала выбрано верно.

Video: detailed calculation of the rafter system

Calculating the rafter system of a gable roof is a whole complex of calculations. In order for the beams to cope with the task assigned to them, the builder needs to accurately determine the length, quantity and cross-section of the material, find out the load on it and find out what the pitch between the rafters should be.

The gable roof is the most popular design in private housing construction. The rafter system of a gable roof must provide a supporting platform for the installation of the roof. A correctly calculated pitch of the rafters of a gable roof allows you to ensure the strength and stability of the structure to all external loads, and create a durable and reliable roofing covering. This article discusses design features rafter system, calculation and installation procedures. This information will allow you to correctly understand the methodology for creating a gable roof, so as not to ask workers unnecessary questions during construction.

Distance between rafters for a gable roof

Among people involved in the construction of a private or country house, there are constantly discussions about the most good design roof and the number of supporting elements. To understand these opinions and take one side or another, it is necessary to consider general device roofs.

There are two types of rafter construction:

Hanging.

Layered.

Apply to relatively small houses with a length of supporting elements of no more than 6 m. The structure consists of a number of trusses having the shape of an isosceles triangle. The trusses are installed on a timber frame (mauerlat) and connected to each other by sheathing strips. Load bearing capacity hanging rafters relatively small, but simplicity of design, cost-effectiveness and high speed of installation are their advantages. There are quite a few options for implementing hanging rafters, which is explained by the prevalence of small buildings that do not require a complex and massive roof structure.

Design layered rafter system somewhat more complicated. A strong beam - Mauerlat - is laid along the perimeter of the upper floor. Two (or more) are installed along the longitudinal central axis vertical racks, the height of which determines the angle of inclination of the slopes. A ridge purlin is installed between the racks, which runs along the entire length of the roof and serves as a reference line for the rafter legs. Each of them has two support points - at the bottom there is a mauerlat, and at the top there is a ridge girder.

To form additional support that prevents sagging of the supports, struts are used - inclined strips attached to the rafters at an angle close to a straight line and resting at the bottom on the central bottom beam- lying down.

The roof lag pitch is the distance between two adjacent rafters. It is determined by the number of logs evenly distributed along the length of the longitudinal axis of the roof. The main supporting structures for the roof are rafters and sheathing, forming inclined surfaces with a given geometry and area. The angle of inclination determines the wind and snow loads, and as the angle increases, the wind load increases, and with a decrease, the snow load on the roof.

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What determines the pitch of the rafters?

Let's consider the factors that determine the pitch between the rafters gable roof, more details. It is necessary to immediately take into account that the number of rafters determines the load-bearing capacity. Reducing their number complicates the installation of insulation and contributes to the sagging of the sheathing strips and the roof installed on them.

At the same time, placing rafters too often also creates difficulties when installing insulation. It has to be adjusted in width, which creates waste, i.e. waste of material. Therefore, the size of the heat insulator is often used as a criterion for determining the pitch of the rafters. For example, many types of mineral wool are 60 cm wide, which is quite suitable for most gable roof designs.

In addition, the pitch of the rafters directly depends on their number. This is a calculated value, which is determined based on the load-bearing capacity of the supporting elements. The loads acting on the roofing covering, as well as the weight of the covering itself, are quite large, so to accommodate them you need a stable and robust design. It must be taken into account that the type of rafter system also matters, since layered rafters are much heavier than hanging rafters, they form a noticeable load on the walls and foundation of the house.

Wind and snow loads are external factors, affecting the roof structure. Snow weight in winter period capable of pushing through or even breaking the roof if its design is not designed properly. SNiP annexes contain special data on the average annual amount of snow in different regions. In some of them there is up to half a ton of snow per square meter.

In addition to snow, wind creates serious loads. Moreover, if the snow load is static, then the wind effects are sudden and uneven. The wind can rise at any time of the year, both winter and summer, which makes us take it very seriously. When choosing an angle of inclination, you should find out the strength and direction of the prevailing winds in the region, and find out about the possibility of hurricane gusts. SNiP is available in the appendices.

All these factors determine the parameters of the rafter system and the distance between the individual supports.

Dependence of rafter pitch on roofing material

There are a large number of types of roofing coverings. Most of them are noticeably outdated and little used in modern construction. The most popular today are:

Profiled sheet.

Metal tiles.

It is necessary to take into account that corrugated sheets and corrugated sheets represent one group of profiled coating. Some sources consider them to be different names for the same material, others divide them by wave height. The corrugated sheet has a higher wave height, and the corrugated sheet is somewhat flatter. The first type can be used not only as a roofing covering, but also as a material for the construction of fences, fencing, metal garages and so on.

Corrugated sheeting has a smaller wave and is intended for installation as a roof. Both materials have a common specific feature - profiling is performed only in the longitudinal direction, which expands their capabilities and makes it possible to make roofing for round roofs and canopies.

The pitch of the rafters of a gable roof under corrugated sheeting is selected taking into account this feature of the material. If the value is too high, there will be a possibility of the roof sagging between the rafters. In addition, there will be excessive load on the sheathing strips, which may not be ready for it. The area of ​​the slope also becomes an important parameter. Rafter pitch pitched roof under corrugated roofing is much less than for a gable roof, since the length of the supporting elements and the magnitude of the load increase significantly and require an increased number of supports.

Metal tiles look like natural ceramic tiles. In all its operational qualities, it is very similar to corrugated sheets or corrugated sheets, but in physical terms it has important feature– the presence of not only longitudinal, but also transverse waves. This allows you to slightly increase the pitch between the rafters of a gable roof under metal tiles, or to be guided by the size of the heat insulator when choosing.

When using slate or ondulin, the pitch of the rafters is taken according to the degree of rigidity of these materials. As an option, increase the density of the sheathing, or install solid version made of thick plywood.

Method for calculating the distance between rafters

There are two calculation options:

Engineering calculation using appropriate formulas and techniques.

Using online calculators giving an answer after entering their own initial data.

The first method is only suitable for a professional designer roofing systems. For an untrained person, it is extremely difficult to perform such calculations, since various specific data, coefficients, table values, which are difficult to find and must be used correctly. Calculations obtained using online calculators are also not recommended for use in real construction, but should be used as an option for clarifying or checking the results of calculations performed by specialized organizations.

Video description

In the video you can see what the pitch of the rafters should be:

Conclusion

In conclusion, it is necessary to recall that all design and calculation activities must be carried out by trained and specially trained specialists. The pitch of the rafters is an important and critical quantity that determines the load-bearing capacity of the roof. The destruction caused by the inability to accept existing loads is quite serious and can call into question the possibility of living in the house, so it is necessary to take this issue as seriously as possible.

The distance between the rafters is one of key parameters, affecting the strength of the structure. Proper calculation of the installation pitch of the rafters allows you to build a roof that is resistant to high operating loads.

Roof loads and calculation of the rafter system

The development of a project for a single-pitch or gable roof begins with choosing the type of rafter system, the angle of inclination of the slopes (roof height) and materials for constructing the structure. Calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Constant loads include:

• the weight of the materials from which the rafter system is made;
• roofing weight;
• weight of roofing materials (waterproofing, vapor barrier, insulation);
• weight of finishing elements of a residential attic or attic.

In addition to permanent loads, the roof also experiences temporary loads, which include:

weight of snow cover;

the weight of a person during roof maintenance and repair.

The pitch refers to the distance between the rafters of one slope. When calculating a single slope, gable or complex roof, usually follow the following scheme:

• the length of the future roof slope is measured;
• the resulting value is divided by the optimal numeric value rafter pitch;
• one is added to the resulting value, the result is rounded;
• the length of the roof slope is divided by the rounded result.

The final result will allow you to determine at what distance the rafter legs should be placed. Determining the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, installation features of the sheathing under different kinds roofing material. If a roof with a chimney is being designed, the pitch can be adjusted taking into account its location, so that you do not have to subsequently remove part of the rafters and install a supporting structure, such as a special rafter system.

Distance between rafters under slate

Slate is a traditional roofing material. Its advantages include characteristics such as resistance to external influences(excluding mechanical) and low cost. Slate allows you to create a roofing covering, the repair of which can be reduced to replacing individual elements. Slate is heavy and requires the installation of a fairly powerful rafter system. Calculation of the distance at which it is necessary to place the rafters under the slate is carried out taking into account the cross-section of the beam for the manufacture of rafter legs.

The optimal solution is to install a system under slate, in which the gap between the rafters should be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the sheathing is made of timber or boards with a cross-section of at least 30 mm. When calculating a rafter system for slate, you should read that this material has quite large restrictions on the choice of the angle of inclination of the slopes.

Rafters for metal tiles

Metal tiles are actively used as a practical and aesthetic roofing material when arranging a pitched, gable, hip or complex roof. The frame for metal tiles is built according to standard principles. To calculate at what distance it is better to install the rafters, it is necessary to take into account the loads and the angle of the roof. Metal tiles are characterized by their relatively low weight, thanks to which they can serve as a replacement for old slate or ceramic tile roofing. In this case, the rafters will not need to be strengthened or the pitch of their installation changed.

The standard pitch of rafters for metal tiles is 600-900 mm. The cross-section of the elements can be 50-150 mm - this is enough to create a reliable frame for metal tiles. But if you plan to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, for rafters under metal tiles it is recommended to use 200x50 timber so as not to install additional system holding the insulation. It is better to adjust the gap between the rafters for metal tiles to the width of the sheet or roll insulation.

Corrugated sheeting: rafters and sheathing

Corrugated sheeting is a lightweight and easy-to-use roofing material. Galvanized or coated with a decorative protective layer, corrugated sheets can be used for installation pitched roof a utility room or garage, as well as for a gable roof of a residential building. How to calculate the distance required to install rafters under corrugated sheeting?

To ensure the necessary structural rigidity, it is enough to install the rafters under the corrugated sheets in increments of 600-900 mm. In this case, you need to pay attention to the angle of the roof. Calculations show that under high external loads, it is better to lay corrugated sheets on the system with a minimum step. But if the distance between the rafters under the corrugated sheet is close to the maximum, and the roof slope angle is small, then the structure is strengthened by using more frequent sheathing. In this case, the pitch of the sheathing under the corrugated sheet should be about 50 mm, the width of the elements should be at least 100 mm.

Rafter system for soft roofing

Soft roofing includes bitumen and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. Soft roofing is characterized by relatively low weight and the absence of the need to install massive truss structure.

The minimum distance between the rafter legs is 600 mm, the maximum is 1500 mm. When installing a support under soft roof it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous sheathing should be. The choice of step is also influenced by the thickness of the material for the sheathing - the thicker the sheet of plywood or OSB, the larger the installation step of the rafter legs can be.

Ondulin: calculation of rafters

Ondulin (bitumen slate) is laid on a flat, continuous sheathing made of sheet material. This allows the roofing covering to successfully resist wind and snow loads. The sheathing for ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or pitched roof.

Rafters for ondulin are made of timber with a section of 200×50 mm. When choosing at what distance to place the rafter legs for the structure under the ondulin, it is recommended to take into account the width insulation material to make it easier to install. This calculation allows you to reduce the financial costs of roofing.

Sandwich panel roof

Sandwich roofing is most often erected on houses made of sip panels or hangar-type buildings. A special feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the top of the wall (or the distance between the supporting structures of a gable roof) allow the installation of a sandwich without additional supports.

If the span exceeds 4 meters, additional purlins must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case, the rafters can be positioned at larger intervals - they serve as a support for the purlins. The distance between the rafter legs is selected based on the length of the available material for the purlins and the length load-bearing walls. Technical specifications sandwich allow the roof to withstand high operating loads.

Polycarbonate: construction of a supporting structure

Polycarbonate in Lately is actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, canopies, and winter gardens. The lathing and rafter system for polycarbonate can be made of wood or metal.

Polycarbonate varies in weight depending on the thickness of the sheet. It is recommended to perform lathing under polycarbonate in increments of 600-800 mm. The lathing (wooden or metal) is mounted on rafters, which can be straight or arched. Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to lower the rafters, it is necessary to take into account the glazing area, the size and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.

The distance between the rafters of a gable and pitched roof

Find out what distance between the rafters needs to be made for a gable and shed roof. The maximum distance between rafters for metal tiles, ondulin and soft roofing.

Distance between rafters: principles and examples of calculating the pitch of a rafter system

The task of correctly calculating the distance between the rafters is a very important one. How seriously you begin to solve this problem will determine not only the reliability and durability of the roof, but also all subsequent work on it: laying insulation, installing roofing, installing additional elements. If you manipulate the pitch of the rafters under the roofing sheets, as many do, then it is not a fact that insulation will then fit between the rafters. If you focus only on insulation, the very first winter with its abundant Russian snow will crush the rafter system. That's why the whole point is to pick optimal step rafters for all slopes, and this is the skill we will teach you now.

What determines the pitch of the rafters?

So, the distance between the rafters is determined by the following important factors:

1. Roof shape (gable, single-slope or multi-slope).
2. Roof angle.
3. Parameters of the timber used to make rafters (width, thickness).
4. The design of the rafter system (sloping, hanging or sliding).
5. The totality of all loads on the roof (weight of covering, atmospheric phenomena, etc.).
6. Lathing material (20x100 or 50x50) and its parameters (solid, with gaps of 10 cm, 20 cm or solid plywood)

And each of these parameters needs to be taken into account, which is exactly what this article is about.

Decorative rafters: 0% load

First of all, decide on the most important point: the type of roof and its purpose. The fact is that in winter the roof of a residential building can withstand a large cap of snow, a constant wind at altitude, and it is often insulated from the inside, but completely different requirements are placed on the rafter system of a small gazebo hidden under the treetops.

For example, if you are building a pergola in its classical sense, then it does not matter at all what exactly the distance between the rafters will be - this is a purely aesthetic factor:

The illustration above shows that even such a building has its own pitch of rafters. After all, here it provides both the aesthetic factor and the rigidity of the structure itself. But they choose a step arbitrarily.

Functional rafters: detailed calculation

We come to the main question: what distance should be between the rafters of the roof of a residential building? Here, be patient and carefully study all the nuances.

Point 1. Wall length and choice of rafter spacing

The first step in installing rafters on the roof of a residential building is usually chosen structurally based on the size of the building, although taking into account many other factors.

For example, the easiest way is to install rafters in 1-meter increments, so for a wall 6 meters long, 7 rafters are installed as a standard. At the same time, you can save money by placing them at a distance of 1 and 2 meters, and you will get exactly 5 rafters. It can also be placed at a distance of 2 and 3 meters, but reinforced with lathing. But it is extremely undesirable to make the rafter spacing more than 2 meters.

Point 2. The influence of snow and wind loads on the shape of the roof

So, we settled on the fact that the average distance between the rafters regular roof- 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less flat or simply heavy (for example, covered clay tiles), then this distance must be reduced to 60-80 cm. But on a roof with a slope of more than 45 degrees, it can even be increased by a distance of 1.2 m-1.4 m.

Why is this so important? Let's figure it out. The fact is that the air flow collides on its way with the wall under the roof of the building, and turbulence occurs there, after which the wind hits the eaves of the roof. It turns out that the wind flow seems to bend around the slope of the roof, but at the same time trying to lift it. And at this moment forces arise in the roof that are ready to tear it off or overturn it - these are two windward sides and one lifting one.

There is another force that arises from wind pressure and acts perpendicular to the slope, trying to press the roof slope inward. And the greater the angle of inclination of the roof slope, the more important are the safe wind forces and the less tangential ones. And the greater the angle of the slope, the less often you need to install rafters.

This map of the average wind load will help you understand whether to make a high roof or a flat one:

The second point: in the Russian region on standard roof at home is constantly exposed to atmospheric phenomena such as snow. Here too, you need to take into account that the snow bag usually accumulates more on one side of the roof than on the other.

That is why in places where such a bag is possible, you need to insert paired rafter legs or make a continuous sheathing. The easiest way to identify such places is by the wind rose: single rafters are placed on the windward side, and paired rafters are placed on the leeward side.

If you are building a house for the first time, then you won’t have to decide on your own worldview, but rather determine the average snow load for your area according to official data:

Point 3. The issue of insulation and standard width swear words

If you will be insulating the roof, then it is advisable to set the pitch of the rafters to the standard sizes of insulation boards, which are 60, 80 cm and 120 cm.

Modern insulation materials are now sold in standard widths, usually at the same standard rafter spacing. If you then take them and adjust them to existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.

Point 4. Quality and strength of the lumber used

It is also of great importance what kind of material you use to build the rafter system. Thus, for each type of wood there is its own regulatory documentation that concerns its load-bearing capacity:

Because For the manufacture of roof truss systems in Russia, pine and spruce are most often used; their bending strength and features of use have long been prescribed. If you use wood of other species, you can derive a correction factor.

In addition, if the rafters have sections, notches or holes for bolts, in this place the load-bearing capacity of the beam must be calculated with a coefficient of 0.80.

Point 5. Distance between tie rods and floor beams

One more point: if the roof is built with interconnected trusses, and their lower chord is used simultaneously as floor beams, then the distance between the trusses should be within 60-75 cm in order to take into account the design of the future floor.

Point 6. Loads on rafters

So, here are the main loads that act on the roof truss system:

1. Static, which includes the weight of the rafter system itself, the weight of the roof, the snow lying on the roof and additional elements.
2. Dynamic, which includes wind force, unexpected damage to the roof, the weight of a person and equipment for repairs, and similar factors.

And all these factors are capable of influencing the roof simultaneously at a certain moment, and therefore there is such a thing as critical value. This is exactly the load value at which the roof cannot withstand and becomes deformed.

Therefore, if a building is being built with significant spans, then steel roof trusses. The fact is that there is no longer any tension in such rods, and the entire load falls on the nodes - here they are affected by compressive and tensile forces. And the distance between such trusses is calculated depending on the type of roof and the design of the roof itself.

Typically, a unified truss is installed with a span that is a multiple of six, and therefore a distance that is a multiple of one and a half meters is made between the nodes of the truss.

Point 7. Weight of the rafter system and roofing pie

Do not forget that the main purpose of the rafters is to support the entire roof, and its weight is decisive:

Point 8. Ease of installation of roofing

The distance between the rafters is also influenced by factors such as the selected roofing covering. The higher the roof slope, the more roofing materials will be used. And the heavier they are, the more often you will have to put rafters under them. But what about the continuous sheathing? The fact of the matter is that it also has its own weight:

Each type of roof has its own optimal rafter pitch. After all, many standard sheets at the edges need to be fastened directly into the rafters or sheathing, and it is important that they coincide. Otherwise, the work of covering the roof will easily turn into a living hell at altitude, believe me.

That is why, even before starting installation, you must make a layout and check everything several times. And know some important subtleties for each type of coating.

Determination of the totality of loads on the roof as a whole and the rafters separately

So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof rafter system: the weight of the rafter system, the snow cap, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all plan for the unexpected favorable conditions, that is, to provide an additional 10% percentage strength.

Now all you have to do is divide the total load by the planned number of rafters and see if each of them can cope with its task. If it seems that the structure will be frail, feel free to add 1-2 rafters to total, and you will be calm about your home.

You need to make calculations for destruction, i.e. for the full load acting on the roof. All these loads are determined by technical specifications materials and SNiPs.

The standard roof structure consists of rafters, lattice purlins, and each of these elements responds only to the load that puts pressure on it, and not on common roof generally. Those. Each individual rafter is subject to its own load, total, but divided by the number of rafter legs, and by changing the step of their location, you change the area where the load is collected on the rafters - reducing it or increasing it. And, if changing the pitch of the rafters is inconvenient for you, then work with the parameters of the section of the rafter legs, and the overall load bearing capacity the roof will increase significantly:

When making this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splice along the length. Now let's explain in more detail. So, on roofs with slopes up to 30 degrees, the rafters have so-called “bending elements”. Those. they work specifically for bending, and there are certain requirements for them. And the possibility of rafter deflection is calculated using a special formula, and if the result exceeds the norm, then the rafters are increased in height and a new calculation is made again.

But on a roof with a warehouse slope of more than 30 degrees, which rafters are already considered “bending-compressed” elements. That is, they are affected not only by a uniformly distributed load, which causes the rafters to bend, but also by forces that are already acting along the axis of the rafters. Speaking in simple language, here the rafters not only bend a little under the weight of the roof, but are also compressed from the ridge to the mauerlat. In addition, the crossbar, which usually holds the two rafter legs, must also be checked for tension.

As you can see, even a person far from construction can handle such calculations. The main thing is to take everything into account, be attentive and ready to spend a little more time on design, so that then all the work goes like clockwork!

Distance between rafters: what step should be between rafters

Detailed instructions on how to correctly calculate the distance between the rafters of roofs of different designs, taking into account the amount of loads and the material used.

When building a house, it is important that the roof frame and its truss structure are reliable. To do this you need to know optimal sizes gap between the rafters. Our experts will tell you in this article how to correctly carry out calculations for the rafter system of a gable roof, taking into account various roofing materials.

How to correctly calculate the distance between the rafters (for a gable roof)

Distance for different roofing materials

Experts advise: determining the step between rafter supports, take into account the roofing material from which the roof of the gable roof will be created. Let's look at the most common roofing options suitable for private residential buildings.

1. Corrugated sheeting - for this roofing material, the digital distance we need is from 60 to 90 centimeters (if the pitch is increased to at least one meter, we will have to install additional transverse boards with a larger cross-section - 5 × 10 cm). In this case, under the corrugated sheeting you will need to install a sheathing, which will provide the ability to attach the required vertical components - a chimney, a ventilation system.
2. Ceramic tiles - roofing made from this material is quite heavy, so the load on the rafter system will be higher than when covering the roof with corrugated sheeting. Accordingly, the distance that we calculate will be different: from 80 centimeters to 1 meter 30 centimeters. But in this option, the steepness of the roof slope is also taken into account (if the slope angle is 15 degrees, then the gap will be minimal - 80 cm, at 75 degrees - 130 cm).
3. Metal tiles - this roofing material is lighter than the previous one and is sold immediately in leaf form, therefore, the thickness of the components of the rafter system is reduced, and, consequently, the distance between the elements in it is reduced. For rafter material with a cross section of 15 × 5 centimeters, the gap should be selected from 60 centimeters to 95 centimeters. This distance will allow for high-quality insulation attic space(for this it is necessary to place the insulation material directly between the rafters). The peculiarity of installing a rafter structure under metal tiles is that the supports are installed on top of the ridge girder (usually they are installed on the side of the ridge beam). But in this case, you should not forget about the ventilation holes near the upper roof.
4. Ondulin - this material is called “Euro slate”, and it is perfect for roofing private residential buildings. For the rafter structure under the ondulin, rafters from boards 5 × 20 centimeters are used, which provides a certain margin of safety (the rafter purlins are also taken into account). The distance between such rafter boards is standard - from 60 to 90 centimeters, and the wooden beam for the sheathing should have a cross-section of 4 × 5 cm, with an interaxial step of 60 cm.
5. Slate is one of the most common roofing materials in our country; rafters for it should be selected with a cross-section of 5 × 10 / 5 × 150 centimeters. The distance between them will be in a slightly smaller range - 60-80 cm. The lathing is made of wooden beam has its own gap between the elements, which directly depends on the slope angle of the roof slope: for a small slope - from 45 cm, for a larger slope - from 60 cm.

Thus, the general digital indicators for determining the distance between the rafters (depending on the roofing material) will fluctuate within the following limits: the minimum is 60 cm, and the maximum is 130 cm. If you yourself cannot decide on the choice of such a digital indicator, then you should contact To qualified specialists for help.

Rafter system is undoubtedly the most important structural element any pitched roof. The consequence of its incorrect installation can be not only deformation of the roof, requiring expensive repairs, but also a complete collapse of the roof on the head of the insolvent builder.

The stability of the rafter system to various loads is influenced by the following four main factors:

1. fastening strength rafters to the ridge and mauerlat;
2. correct calculation of the supporting structure for rafters depending on the span length;
3. choice rafter material;
4. step between the rafters.

The topic of this article is the choice of material and pitch between rafters, taking into account the intended type of roof.

What are the calculations based on?

When making calculations, four main indicators are taken into account:

design features of roofing material;

span length between supports;

rafter leg mounting angle.

The most important thing is to calculate the maximum roof load, consisting of:

• rafter weights,
• sheathing weight,
• weight of roofing material and insulation,
• snow load ( reference Information, unique for each region),
• wind load (also reference information),
• person’s weight (if repairs or cleaning are necessary, 175 kg/sq.m).

To carry out accurate calculations, experts use special formulas from strength-of-material materials, but when constructing a private one, you can use approximate recommendations.

Method for calculating the distance between rafters

Calculation of exact distance between the rafters is based on the results of a preliminary calculation of the maximum allowable step. To make this calculation, the total load, the roof structure and the material used for the rafters are taken into account.

Method for calculating the pitch of the roof frame:

1. Measure the length of the roof from end to end.
2. Received distance divided by the maximum step size.
3. Round the resulting value to a higher integer. This is the number of rafter spans.
4. Divide the total length of the roof by the number of spans. This is the required rafter pitch size.
5. Add one to the number of spans.This required amount rafters

For some types of roofing material It is advisable to use fixed distances between the rafters; in this case, an additional rafter with a non-standard pitch is installed at one of the ends of the roof.

Rafter pitch depending on material

Can be increased as the strength of the material from which they are made increases. Most often, for each roofing material, the required rafter pitch and the permissible cross-sections of the rafter legs, taking into account the load, are indicated.

These recommendations are regional in nature and applicable to the central zone of Russia and more southern regions. Before developing a drawing, you should definitely check the level of wind pressure and snow cover in your region, and adjust the pitch and/or cross-section of the rafters.

In those regions where the snow load significantly exceeds the wind load, the use of sloped roofs is recommended 35 – 45 degrees.

Rafter system in private homes it is most often made from logs with a diameter 12 – 22 cm, timber/board thickness 40 – 100 mm and width 150 – 220 mm. When making calculations, it is possible to use, instead of logs of a certain diameter, beams of similar width, thickness 100 mm.

Rafter structure for corrugated sheets

Rafter structure for ceramic tiles

Ceramic tiles has significant differences from other types of roofing materials that must be taken into account when designing the rafter systems for it:

• 5 – 10 times more weight, resulting in doubling the weight of the entire roof. This leads to the need to use a frequent step ( 0.6-0.8 meters) and the cross-sectional area of ​​the rafters increased by 25%.
• Fine-grained nature of the material. Increases the requirements for the accuracy of installation of the transverse lathing. The pitch of the sheathing beam, permissible sections and installation angles are always indicated in the instructions for each specific tile model.

There are tile models designed for installation at an angle 12 – 60 degrees, ordinary models are recommended to be mounted at an angle 20 – 45 degrees. Timber is most often used for lathing 50x50 mm.

Rafter structure for metal tiles

Metal tiles essentially represents less rigid and more light decorative option of corrugated sheeting, therefore the requirements for the rafter system, in particular for the recommended sections of rafter legs, largely coincide.

Features of the rafter structure for metal tiles can be called a significant reduction in the pitch of the sheathing, which should be equal to the length of the longitudinal wave (30 cm for most types). This leads to the need to reduce the distance between the rafters up to 0.6 – 1 m, to reduce the cost of lumber for sheathing. The angle of the roof slope is selected from 22 to 45 degrees.

Rafter structure for ondulin

Ondulin– slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:

• permissible installation angle – 5 – 45 degrees;
• distance between rafters – 60 cm at an angle of up to 15 degrees, up to 90 cm at an angle of more than 15 degrees;
• sheathing - solid plywood on a slope up to 10 degrees, board 30x100 mm in increments 45 cm on the slope 10 – 15 degrees, timber 40x50 mm in increments 60 cm on the slope above 15 degrees.

Considering the light weight of the material, the cross-section of the rafter legs is selected based on the same recommendations as for corrugated sheeting.

Rafter structure for slate covering

Slate- a traditional, fairly rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change recommendations for the optimal design of the rafter system towards the use of more durable elements and increasing the step between them:

• Due to low tightness, it is not advisable to use slate roofs with a slope angle of less than 22 degrees. If it is necessary to install such a roof, you can use the recommendations for installing ondulin as instructions, adjusted for the universal sheathing pitch - 55 cm.
• Permissible angle for installing rafters under slate - up to 60 degrees.
• The installation step is selected from 0.8 to 1.5 m, depending on the cross-section of the rafter leg, the load and the presence of sheathing material.
• The material for the rafters is selected with a slightly larger cross-section than for light roofs. For the most popular step 1.2 m a beam is taken with a section from 75x150 to 100x200 mm, depending on the length of the span between the supports.
• Material for sheathing selected in accordance with the distance between the rafters - timber 50x50 mm up to 1.2 m, timber 60x60 mm – 1.2 m and more.
• Lathing step is selected in such a way that each sheet lies on three beams and overlaps 15 cm with the neighbor. Considering the standard sheet length 1.75 m, step is used 80 cm.

Rafters for single-pitch and gable roofs

What is the rafter distance for a pitched roof? Shed roof does not require a complex rafter structure. The rafters are laid from wall to wall, most often without using a mauerlat, directly on the crown.

No additional ribs stiffness sets the maximum slope angle – 30 degrees and permissible span length - less than 6 m(for wooden rafters). Optimal angle – 15 – 20 degrees.

Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where wind pressure is comparable to the snow load, correct installation of a pitched roof “downwind” can lead to self-cleaning of the roof.

Gable roof is a system of parallel triangles connected to each other by a mauerlat and a ridge. There are many elements for firmly fastening the sides of the triangle together and transferring loads from the rafter legs to the walls - racks, couplers, jibs, support beams, and so on.

The step between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. The approximate step between the rafter legs is 1-1.2 meters

Strength of a rigid triangle increases as its shape approaches an isosceles one, therefore, with increasing slope angle up to 60 degrees you can expand the spacing between the rafters.

However, this will also lead to an increase in material consumption and to a multiple increase in the roof windage. The optimal slope angle for snowy regions is 45 degrees, for windy people – 20 degrees.

Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofs step rafters should be from 60 cm to 1 m.

• The correct fastening of the rafters is no less important than the correct calculation of the structure. Before self-installation roofing, it’s worth taking a lesson from an experienced carpenter and reading educational literature.
• When choosing the pitch of the rafters, do not forget about thermal insulation. All types of insulation can shrink a little, so you can buy them by approximate size. The most commonly produced sizes are 60, 80, 100, 120 cm.
• For roofs with a slope of 45 degrees or more, the weight of a person on the roof can be ignored. This removes 175 kilograms of the design load per square meter and allows rafters to be installed on average 20% less often.
• Snow and wind load in Russian regions can be found by regulatory documents– maps in the application AND To .
• There are many online roofing calculators on the web., capable of, if not correctly calculating all the nuances, then at least advising on the selection of the correct section for the rafters.