What step should be between the rafters. The distance between the rafters: the correct calculation

The roof structure is one of the main enclosing elements of the building, the quality characteristics of which are subject to rather stringent requirements.

One of the most common roof sheathing materials is metal shingles, which are made from thin sheets of steel, aluminum, or copper.

From above, the elements are equipped with a polymer coating, which protects metal from aggressive external influences.

Externally, the metal tile is similar to ceramic, but it is more durable. This material is used to cover pitched roofs, the slope of which must be at least 14 degrees.

This is the national team roof frame structure, consisting of many wooden or metal parts. She is rests on load-bearing walls, which are a reliable basis for all overlying elements. The rafter system serves as a kind of skeleton, on the basis of which it is made, - and the roof, as well as laying the roofing finish roofing layer.

truss system

The constituent elements of the truss roof, and their main characteristics:

• Mauerlat. A softwood beam, which is a connecting element between the rafters and the underlying structures. It has a square cross section with a side of 100 or 150 mm. Mauerlat is laid along the load-bearing wall along its entire length. With the help of the Mauerlat, the loads from the roof are evenly distributed throughout the building.
• Sill. A beam having a square section similar to a Mauerlat. It is laid transversely to the bearing walls, as it serves to redistribute the load from the roof racks.
• Rafter leg. From these elements, the main triangular roof structure is created, which experiences the full severity of external atmospheric influences (rain, wind, snow, hail, etc.).
• Rack. Vertical connecting elements that distribute compressive loads from the ridge assembly over the entire area of ​​​​bearing walls. They are made of square bars, the length of the edge of which is determined by calculation.
• Puff. It is the final horizontal element of the triangle of rafter legs, which does not allow them to creep under the pressure of external loads and the own weight of the roof. It is used in systems with hanging rafters.
• Struts. Perceive and redistribute bending loads from the ridge assembly.
• Crate. It consists of boards, bars or plywood sheets (in the case of subsequent laying of bituminous tiles), which are located at a right angle relative to the rafter legs, while being an additional rigid element.
• . The junction of two roof slopes.
• Overhang. A roofing element protruding from the load-bearing wall structures at a distance of about 0.4 m. Its purpose is to limit the penetration of moisture to the walls.
• Filly. These elements are attached to the ends of the rafters if they are not long enough to organize an overhang.

Varieties of pitched roofs

Depending on the number of inclined planes, roof structures can be divided into:

In private housing construction, the most commonly used option gable roof, since he has a number of advantages. These include:

1. Practicality. The gable roof has a significant angle of inclination, thanks to which rainwater does not accumulate on its surface, and snow and wind loads are distributed in the most optimal way.
2. Ease of device and operation. The assembly and joining of two pitched elements is much easier than with complex roof structures. In addition, the repair of such a roof will also be simple.
3. Aesthetics. A roof with a gable structure is organically written into the surrounding infrastructure.
4. Reliability(if done correctly).
5. Democratic price constituent materials.

Types of pitched roofs

Gable roof - truss system for metal tiles

Frame from rafters under a gable roof from a metal tile has no significant differences from structures with other covering roofing materials.

But, in view of the fact that metal thin sheets have a low specific gravity, the rafters will experience less constant load.

This allows you to reduce the value of their cross section, due to which can save a lot on the purchase of wood materials.

Ideal for metal roofing the angle of inclination must be at least 14 degrees.

For a roof with two pitched elements, the following apply: frame options:

Laminated rafters under a metal tile.

In this case, 2 load-bearing rafter legs are fastened together using lying down(horizontally) and racks(vertically). The bed is laid parallel to the Mauerlat element, while taking on some of the force effects. The rafter system under the metal tile is taken over only bending loads, which significantly affects the selection of the calculated cross section. Such a system can be used for buildings with large and small spans.

Types of rafters

Hanging rafters.

Unlike layered systems, in this embodiment, two rafter legs fastened together only in the ridge knot. In this case, significant bursting forces arise on the supporting elements, which limits the use of hanging rafters only for buildings with a span of not more than 6 m.

They can be made of wood or metal, as well as installed at the bottom (acting as a supporting beam) or at the top of a triangular structure. It is worth considering that the higher the puff is located, the greater the effort it will take.

NOTE!

To ensure the quality of the tightening, care must be taken on the reliability of fastening with load-bearing rafter legs.

Combined variant

Used to create an original roof structure. Includes elements of both hanging and layered systems.

How to calculate the angle of inclination of the rafters?

To implement a gable roof, you need to know a few geometric values ​​of the building, namely:

• Half span - L;
• The distance from the load-bearing wall to the roof ridge (or the height of the support post) - H.

Standard formula: α = arctg(L/H)

Where α is the desired angle of inclination of the roof.

Knowing this value, you can calculate the length of the supporting rafter leg:

l = H/sinα.

Where l is the length of the truss element.

Rafter Angle

How to calculate the load?

To carry out the correct selection of parts of the roof frame, it is necessary calculate live and permanent load values acting on its structural elements.

The constant load includes the weight of all elements, as well as the mass of the load-bearing elements themselves and the crate.

The composition of temporary loading options includes force effects from wind, snow cover, rain masses, as well as the weight of a person (to take into account options for subsequent repairs).

Dead Load Calculation

Roofing cake weight.

It is determined by adding the masses of all its elements, namely steam, hydro and thermal insulation, as well as roofing from metal tiles. In this case, the weight of one linear meter (can be found in the regulatory documentation) is multiplied by the value of its length.

The weight of the truss system.

It is determined by adding the weight values ​​​​of the crate, rough flooring, as well as the supporting frame. The mass of each element is calculated by the formula:

M=V*p,

Where V is the volume of the element, calculated depending on the geometric characteristics of the cross section and the length of the element;

P - The density of the wood used (depending on the species).

Total permanent load \u003d weight of the rafter system + weight of the roofing pie.

Calculation of live loading

Conducted in accordance with regulatory documents ( SNiP 2.01.07-85 "Loads and impacts" or Eurocode "Actions on structures" part 1-4).

To determine the value of the wind effect, the roof structure is conventionally divided by height into several parts. For each of them, the value of the wind load is calculated. To obtain the total wind pressure, they must be summed.

Formula for calculation:

Wm=Wo×k×c,

Where Wm is the value of the wind load;

Wo is the normative value of wind pressure determined from zoning maps;

k - wind pressure coefficient (determined depending on the height according to the regulatory documentation);

c - aerodynamic coefficient (for a gable roof - 0.8).

Determined by the formula:

S = µ×So;

Where So is the normative value of the snow load, determined from the zoning map.

µ is a coefficient that is determined depending on the angle of the roof:

• For α≤30 deg. — µ=1
• For α≥60deg. -µ=0
• For 30≤α≤60 deg. – µ=0.033×(60-α)

Snow load areas

How to choose a beam and calculate the pitch of the rafters under the metal tile?

Determining the value of the cross section of the beam of the truss element is carried out in several stages.

Calculation of the load distributed on each linear meter of the structure:

Qр = L×Q;

L - Step of the rafters.

The L value is calculated as follows:

The length of the roof slope is divided by the estimated step of the structures (for convenience, it is most often taken equal to 1). Then 1 is added to the resulting value. The resulting value reflects the number of rafters that need to be installed on one pitched roof surface. At the last stage, the value of the axial distance between the rafter elements is determined by dividing the length of the roof slope by the number of rafters.

The distance between the rafters under the metal tile - the standard step is 0.6-0.95 m.

Rafter pitch

Then we determine the maximum working area of ​​\u200b\u200bthe rafter leg (Lmax). We proceed to the calculation of the cross section. To do this, we find its height using the formula:

H ≥ 8.6*lmax * sqrt(Qp/(b*r)), with roof slope α<30 град;

H ≥ 9.5*lmax * sqrt(Qp/(b*r)), with a roof slope α≥30 degrees;

Where b is the width of the cross section,

r is the value of the normative resistance of wood to bending loads (determined according to normative documentation depending on the type of wood).

To simplify the calculations, you need to use the standardization table for truss elements (GOST 24454-80 “Softwood lumber. dimensions").

If the inequality is not observed, it is necessary to increase the value of the geometric characteristics of the section and repeat the calculation.

What is the difference between the truss system for cold and warm roofs?

The main difference between these two roofs is the support system of the truss elements. In the case of a warm attic, the main supporting element is the Mauerlat, as well as the supporting beam system. In a cold roof, rafters are installed directly on load-bearing walls.

Installation of rafters under the metal tile

All installation work on the installation of the roof is carried out at a sufficiently high height. To minimize the risk of falls, as well as greatly simplify work at height, you can assemble the frame of the supporting truss system on the ground.

To do this, you need to create a template from the boards, according to which further assembly will be carried out.

It is made in several stages:

• The boards are raised above the walls of the building, leveled, and then fasten together with the help of a nail.
• Align the angle of the boards in accordance with the project, by lowering and raising them. The elements are fixed.
• The result should be a structure that resembles in shape the future truss system, made in accordance with the estimated geometric dimensions of the roof.
• The template is lowered to the ground, in accordance with it, the finishing elements are fixed to each other. More details in the video below.

Then you should take care of installing the support element - Mauerlat. As mentioned earlier, it is laid on load-bearing walls in the longitudinal direction. Fastening is carried out using studs (on an armored belt or masonry) or using a wire rod (for buildings with a small roof height).

CAREFULLY!

When using a hairpin connection, connecting elements do not need to be tightly sealed into the wall. They should protrude from the wall by 30-40 mm, as the nut will be screwed onto the studs.

The next step is to create ridge run, serving as a supporting part for the entire structure of a gable roof. It is made from timber or hewn logs. If the span of the building is not more than 6 m, it can be supported without additional supporting elements. Otherwise, construction trusses must be used for installation.

Mounting. Part 1

After installing these elements, it is possible to lift and install the main truss element, assembled according to the template. Fastening with a Mauerlat can be carried out in 2 ways:

Rigid connection. It is carried out with the help of corners and beams. Less often, fastening is used by means of washing down on rafter legs, followed by fixation with nails or staples.

Features: in addition to the main connection, it is necessary to tie the rafters to the wall using anchors or a wire structure.

Sliding. It is based on the creation of a swivel joint. It is made by joining elements using cuts. The elements are connected with a metal embedded part with holes for bolts, or with 2 nails that need to be hammered in at an angle.

It is necessary to carry out the installation of wooden trusses in a certain sequence. First, extreme trusses are installed, located at the ends of the building. Then a cord or rope is pulled between them, with the help of which the verticality of their installation is checked. Further, under the cord, further installation of truss structures is carried out in accordance with the specified design step.

Mounting. Part 2

Creating a roof from a metal tile is a rather laborious process that requires certain skills and a full hand. Therefore, for proper installation, you must at least work under the supervision of a competent specialist.

Useful video

Video instruction for self-installation of rafter legs:

The shed truss system came to us from the USA and Europe. Residents using it noted reliability and cheapness, so the popularity of this type spread very quickly. Despite the fact that a small amount of wood was required for the construction of one slope, few people dared to build such a construction. The fact is that most developers considered such a system too simple for residential buildings, while the other part simply did not know how to build it to prove the opposite. In this article I will try to explain to you how to easily and quickly create such systems and correctly select the pitch of the rafters of a pitched roof.

Basis of calculation

Despite its simplicity, one slope must meet all the installation rules. After all, if serious mistakes are made at the same time, then the roofing will deform, which will inevitably entail not only leaks, but also the collapse of the entire roof.

To achieve maximum stability of the roofing system, it is necessary to pay attention to four components:

1. Reliability of fastening of the rafter legs to the support beam and ridge;
2. Proper selection of auxiliary parts for the truss system;
3. Durable lumber and auxiliary elements;
4. Rafter step.

Do not think that by observing only four points you will achieve the most stable design. To do this, you will have to use all known methods and technologies.

Calculation values

You can’t perform calculations without knowing certain indicators, right? Therefore, before starting, you need to make sure that you have four basic values.

In addition to all these indicators, the main task of any project is to calculate the maximum allowable load on the roof. It includes quite a lot of values, and here is a list of elements whose mass is especially important in the calculation:

• rafter legs
• crate
• roofing cake

If you are far from the construction industry, then you will have to remember that the calculation of the maximum roof load consists of two parts. The first one takes into account all the materials used, and the second one contains the snow load of your region. Its meaning is written in a special reference book, which you can easily find on the net.

But even on this, the indicators will not be accurate, because you forgot about the wind load and the weight of the worker himself, who will carry out installation work and subsequent maintenance (repair, cleaning).

When developing a project by a construction organization, they use complex formulas of strength of materials, so if you don’t want to bother with this, you can use the recommendations of experienced people.

How to calculate the required distance between the rafters

The distance between the rafters of a shed roof largely depends on the previously calculated maximum possible step. To determine this value, you will need to have a total load value, roof parameters and data on the wood of the rafter legs.

You can calculate the optimal step of the rafter leg using the following method:

1. First of all, you need to find the total length of the roof. This value must include any ends and overhangs;
2. The resulting value is divided by the maximum allowable distance between the rafters;
3. The answer is rounded up. This number will indicate the number of spans;
4. Next, we take the value of the length of the roof and divide it into spans. So you will find the optimal step;
5. And to find the number of rafter legs, you need to add one to the spans.

This rule works for the vast majority of roofs, but there are those that cannot be calculated in this way. If you have just such a case, then you will have to acquire an additional rafter on one of the ends.

Rafter system depending on the roofing

It's no secret that the greater the mass of the roofing, the greater the number of rafter legs must be installed. Most manufacturers of this material in the instructions for their product indicate the optimal number of rafters and their dimensions.

You should not blindly trust these instructions, only if you do not live in the central strip of Russia, because they were written specifically for this territory. Before developing a drawing, it is necessary to carefully study the prevailing winds and draw a kind of rose, which will be a guide for future construction.

It is worth noting that in regions of the country where a large amount of precipitation in the form of snow falls, it is best to create steep roofs with a slope of 35-45 degrees. This will provide fast natural gathering snow cover from the surface.

In most cases, the truss system of private houses is created from logs with a diameter of 12 to 22 centimeters, timber or boards with thicknesses from 40 to 100 and widths from 150 to 220 millimeters.

Rafter system for corrugated board

Roofing corrugated board is a fairly light material and at the same time has good strength characteristics. Therefore, as rafter legs, you can use lumber of a small section, but with a frequent step: 0.6 - 1.2 meters. The roof slope should be at a slope of 12 to 45 degrees.

The required section can be selected based on the span distance between the supports. If the distance is about 3 meters, then the section can be taken 40x150 millimeters, at 4 meters this value increases to 50x180 millimeters, and at 6 meters it is necessary to use lumber whose section is 60x200 millimeters.

By the way, the crate in this matter also plays an important role. In the case when the rafter step is a decent value, you will have to use wider boards. For example, for a step of 0.6 meters, elements with a section of 25x100 millimeters will be needed, and for 1.2 meters - 40x100.

The crate for corrugated board is arranged discharged method, and the step of its elements should be 50-80 centimeters. However, these values ​​\u200b\u200bmay go beyond due to the characteristics of the roofing itself. You can also find tips on how to arrange these parts in the instructions that came with the purchased material.

Rafter system for ceramic tiles

Ceramic tiles are a unique roofing material. It is made of clay, which makes this material very heavy. The designed truss systems must necessarily follow the following requirements:

In the roofing sphere, there are only 3 types of crates. One of them can be arranged at an angle of 12-60 degrees, and the other two at an angle of 20-45 degrees. As elements of the crate for clay tiles, you can most often see a beam with a section of 50x50 millimeters.

Rafters for metal tiles

Due to the fact that metal sheets have a much smaller thickness, you do not have to arrange a serious truss system. Therefore, you can safely follow the advice and recommendations of roofing material manufacturers.

It is worth saying a few words about the only nuance that will allow you to save some lumber. So, it lies in the fact that the minimum step of the crate can be increased to 1 meter. This is due to the dimensions of the sheet material. When a metal tile is tripled, then, as a rule, it is supported by a crate in only a few places, and with a rafter pitch of 0.6 meters, it is impossible to create an “economical” crate, so you have to change it along with the rafter system.

Rafter structure for ondulin

To date, ondulin has given way to more modern coatings, but despite this, developers whose roofs were laid with asbestos slate began to look at this material as a profitable alternative. It is made on the basis of bitumen and fiberglass, has a low weight and high quality.

The truss system for ondulin must comply with the following parameters:

• The slope of the slope should be in the range from 5 to 45 degrees;
• With a small slope, the step of the rafter legs should be minimal: 0.6 meters, and with a steeper roof, this distance increases to 0.9 meters;
• With a sloping roof, say up to 10 degrees, it is necessary to arrange a continuous crate. To do this, it is best to use moisture-resistant plywood, OSB boards or edged boards with a section of 30x100 or a beam of 40x50 millimeters.

As for the section of the rafter legs themselves, it is selected according to the same rules as for corrugated board.

Rafter system for corrugated asbestos-cement sheets (slate)

Surprisingly, everyone knows the roofing material called "slate", because the vast majority of private houses are covered with this particular product. Due to its rigidity and components, this material has a fairly solid weight, so it is necessary to follow the recommendations for the construction of the truss system so that it does not collapse even before the start of operation.

• The low tightness of the finished plane does not allow the use of slate with a slope of less than 22 degrees, this will lead to leaks. If you cannot find any recommendations for the installation of asbestos-cement sheets (which is unlikely), then you can always use the instructions that came with ondulin;
• The maximum possible slope of the rafters with a slate roof is less than 60 degrees;
• The optimal step of the rafter legs lies in the range from 0.8 to 1.5 meters. Here everything will depend on the load and cross-section of lumber;
• As a rule, a wooden system for slate requires a slightly larger section of the legs than with a light roof. An example is the situation when the pitch of the rafters is 1.2 meters. For the rafters, you will have to take a bar with a section of 75x150 or 100x200;
• As for the crate, its elements will also differ from the step of the rafter legs. If it is up to 1.2 meters, then a bar of 50x50 millimeters will do, and with a larger step - 60x60 millimeters;
• The step of the crate beam should be selected so that one sheet is supported by 3 elements. The slate should extend beyond the edges by 15 centimeters on both sides. For example, if we consider the standard dimensions of an asbestos-cement sheet (175 centimeters), then we can use a crate step of 80 centimeters.

It is probably worth remembering that asbestos is harmful substance, therefore, when working with a material that contains its particles, safety precautions must be observed. Which states that the worker must wear personal protective equipment.

Rafter system of one and two slopes

Recently, the shed roof is gaining more and more sympathy. It is understandable, because materials are only getting more expensive, and you want to save money. Due to the simple design, this can be done. The rafter system of one slope is quite primitive. To do this, you just need to put the beams on the crown and secure. Of course, do not forget about the insulating material.

The maximum slope of a shed roof can be 30 degrees, and the span is 6 meters (this rule applies to lumber). The most optimal slope is 15-20 degrees. At this angle, the wind load will not cause much harm, but the snow cover will cause some inconvenience. The solution to this problem can be to place your building "downwind", which will allow it to remove the snow mass from the roof in a natural way.

An alternative option for a single-pitched roof is a double-pitched one. It is a number of rectangles connected together with a Mauerlat and a ridge. It is worth noting one interesting fact. When the shape of a triangle approaches an isosceles one, its rigidity increases. In this regard, with a roof slope of up to 60 degrees, it is possible to expand the step between the rafter legs.

But do not flirt with calculations, because this can lead to an increase in windage and lumber consumption. The most optimal slope of the slopes for a gable system is 45 degrees.

If you decide to build a roof yourself, then you will certainly need some tips that will not only make your work easier, but also increase the operational period of your roof as a whole.

• Calculating the structure correctly is not an easy task, but even if it is done correctly, it can be broken if it is incorrectly fastened. Therefore, mounting the rafter legs in their places, do the work with all responsibility. To improve your skills, you can read information on the network, or invite a knowledgeable person to the facility;
• The step of the rafter legs should not affect the thermal insulation in any way. It is worth remembering that the plates can vary slightly in size. Take advantage of this and push them as tightly as possible. In a hardware store, there are standard sizes of insulation boards of 60, 80, 100 and 120 centimeters;
• For most roofs with a slope of less than 45 degrees, it is necessary to include the weight of the worker in the calculation. As for sharper roofs, this is not necessary, therefore, it is possible to reduce the pitch of the rafter legs by 20%;
• Take advantage of modern technology and calculate your roof with online calculators. All you need is to enter the exact parameters;
• Regulatory documents regarding wind and snow load you can find on the net or from the craftsmen at the construction site;
• Any wood used for construction purposes should be dried as much as possible. This will avoid its deformation in the future.

The roof of a building is one of the most important elements of the entire building. If you start saving on a roofing pie, then soon you will face costly repairs that will affect not only this area, but the entire building as a whole. Therefore, if you want to get the maximum operating period from your comfort, then you should not use low-quality materials.

The roof is one of the main elements of the house, so you should pay special attention to the correct calculation of the roof frame. Which will serve as a skeleton in your home. Incorrect calculation of all loads can lead to disastrous results in the form of deformation of the roof with its subsequent collapse.

Before proceeding with the installation of the roofing, it is necessary to calculate the truss system, which will depend on the material used, construction, and climatic conditions.

What you should pay attention to before making a calculation

Before starting the construction of the roof, it is necessary to choose the type of truss system. Then calculate all the loads that will fall on the roof. The main loads include the weight of the frame, roofing material, insulation, ceiling, and temporary loads are taken into account, among which are the weight of the snow cover, possible gusts of wind, the weight of a person during the installation and operation of the roof.

The distance between the rafters is calculated based on the selected type of rafters and the material with which the roof will be covered.

Types of rafters

In the construction of roofs of various designs, hanging or layered rafters are used. Sloped - used when installing one- or two-slope roofs. They have two points of support - load-bearing walls or a load-bearing wall and a ridge beam. Hanging rafters are used when it is necessary to cover large spans or create a sloping roof. In this case, the rafters rest with one end on the wall, and the other on the opposite rafter. The quality of the material from which the frame is made will directly affect the reliability of the entire roof.

Material for rafters

Currently, wood and metal are used. A wooden beam or log is used in the construction of residential buildings, garages and other buildings. Reinforced concrete or metal rafters are used in the construction of industrial facilities, shopping centers, where wide spans are needed.

Method of calculation

The distance between the rafter legs is called the pitch of the rafters. It should not exceed one meter, and the minimum value - 60 cm. Before making a calculation, it is necessary to measure the size of the roof slope. Then we divide the obtained value by the approximate value of the step between the rafters. One is added to the result and rounded up to the next whole number. So we find out the number of rafters that we need. In order to find out the exact distance between the rafters, for this we need to divide the length of the roof bevel by the number of rafter legs.

For greater clarity, consider an example calculation:

roof bevel length - 28.5 m

the step between the rafters is chosen equal to 80 cm

add one to the resulting number: 35.625 + 1 \u003d 36.625

as a result, we get that we need 37 rafter legs

the exact step of the rafters will be: 28.5 / 37 = 0.77 m

This is a general calculation method that requires adjustment depending on the roofing material.

The dependence of the pitch of the rafters on the material of the roof

The most common roofing materials are slate, metal tiles, corrugated board, ondulin, soft roofing.

Roof truss structure for slate roofs

Slate is widely used as a roofing material, due to its low cost, resistance to temperature extremes. Due to the severity of the material, it is necessary to install a powerful truss system. The distance between the rafters in this case will depend on the cross section of the timber. The optimal value is a distance of 80 cm, which will allow not only to withstand increased weight, but also significant snow and wind loads. In this case, the crate is made with a board at least 3 cm wide. Depending on the type of slate, the crate is made continuous for smooth sheets or sparse for wave ones.

Important: the slate must have at least three support points along the edges and in the center.

Step between rafters for metal tiles

Metal tiles are becoming more and more common among roofing materials. Which is characterized by a simple installation process, and will also help to create your own unique look for your home. Sheets of metal tiles are lightweight, which allow you to increase the distance between the rafters from 600 to 950 mm, with a beam section of 150x50 mm. The crate in this case will depend on the pitch of the sheet wave. So for a wave of 350 mm, a distance between the boards of 30-40 cm is possible.

Important: on the overhangs of the cornices, the edges of the bevels, the step of the lathing is made minimal for greater reliability of the roof.

Rafter pitch under corrugated board

Decking is a galvanized steel sheet coated with a special coating that protects it from the harmful effects of the environment. A large selection of colors and corrugation widths will allow you to create a reliable and aesthetically attractive roof. The step of the rafters under the corrugated board will directly depend on the characteristics of the type of profile used, the angle of the roof, its configuration. You should also take into account the fact that the crate under the profiled sheet is attached perpendicularly. The rafter system is made of beams with a section of 50-75 mm or from a board 20-50 mm thick and no more than 15 cm wide. sparse - the distance between the boards is 50-75 cm. The step of the rafters under the corrugated board is calculated according to the general scheme and is 60-90 cm.

Step of roof rafters from ondulin

Ondulin is a wavy sheet that has high strength and durability. With such a roof, the truss system is made of pine boards with a section of 50x200 mm, in increments of 60-90 cm. A sparse crate of 40x50 cm is made from above.

Important: if the roof has an angle of inclination greater than 50 degrees, then the crate must be solid.

Determining the pitch of the rafters for a pitched roof

A shed roof is simple and does not require any special installation skills from you. Most often it is installed on garages, baths, extensions. The roof frame consists of beams that rest on the walls of the building. The distance between the rafters of a shed roof will depend on the length of the rafters. Here you should correctly approach the choice of the section of the beam, since the greater the distance, the greater the load on the rafters. For the correct selection of the pitch of a shed roof, use the data from the table:

The distance between the rafters for a gable roof

The gable roof is the most common, not only because of the simplicity of the device, but also because of its high reliability. The pitch of the rafters of a gable roof is calculated according to the general scheme. If the bevels are the same on both sides, then one part can be calculated. To do this, we determine the angle of inclination of the bevel, here you should take into account the material with which you will cover the roof. So at an angle of 45 degrees or more, you can use all types of coatings. For slate, tiles, the minimum angle of inclination is 22 degrees, for corrugated board and soft tiles - 12 degrees, for metal tiles - 14 degrees, for ondulin - 6 degrees. The length of the rafters for a gable roof is calculated using the Pythagorean theorem, in which the length is the hypotenuse, and the height of the roof and half of its width are the legs. If the spans are more than 6 meters, then the rafter system is additionally reinforced with struts and headstocks, which will not allow the rafter legs to deform under the weight of the roofing material.

The reliability of the roof and its service life mainly depend on how correctly the calculations are made.

One of the most important parameters of the rafter system is how far apart the rafters are located.

After all, the distribution of the load on the frame depends precisely on this desired parameter.

If the calculation is made incorrectly, then deformation may occur and the roof will collapse.

Therefore, it is extremely important to perform an accurate calculation of the interval between when drawing up a roof project.

Basic provisions of the calculation

The pitch of the rafters is the distance from one rafter leg to the other.

In the construction of roofs of private houses, this value is 1 meter.

But this figure is approximate.

To get the exact size of the interval, it is necessary to calculate the bearing capacity of the truss system of the selected type.

To perform the correct calculation, the following scheme should be used:

• first you need to determine the length of the roof slope;
• now the resulting figure should be divided by the value of the approximately selected rafter step. If you previously chose its value of 1 meter, then you need to divide by 1.

  If 0.8 was chosen, then it should be divided by 0.8, etc.;

• after that, one is added to the result obtained and the resulting value is rounded up. This action is necessary in order to get the exact number of rafters that will need to be installed on one slope;
• the total length of the slope must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.

To better understand everything, let's look at an example.

By measuring the length of the roof slope, we got 27.5 meters.

We choose a step of 1 meter to make it more convenient to count.

Further calculations will look like this:

Now we add the unit 27.5 m + 1 = 28.5 m.

We round up to the nearest value and get the number 29.

That is, 29 rafter legs must be installed on one slope of our roof.

Now we divide the length of the roof by their number: 27.5 / 29 \u003d 0.95 m.

So, in our case, the step of the rafter legs should be 0.95 meters.

This is a general calculation.

In which the peculiarity of a particular roofing material is not taken into account.

And he can significantly change this parameter.

When you know what kind of material you will use on the roof, some changes will have to be made to the calculation procedure.

Optimal and minimum value

The step is the unit of account.

After all, it depends, first of all, on the load on the roof frame and the section of the rafter legs.

You can take a thick board for their construction and make the interval between them 120 cm.

At this distance, the crate may begin to sag.

Yes, and how to lay the heater?

Indeed, for most materials, the width is 1 meter.

So they take an approximate step of 1 meter when calculating.

The minimum distance between is 70 cm.

And to obtain the optimal value for each material, it is necessary to perform a calculation.

Determining the pitch for a pitched roof

Shed roofing is the simplest.

Indeed, in the truss farm of such a roof there are only rafter legs.

There are no struts, racks, braces in its design.

Such a roof is usually arranged on garages, outbuildings, baths.

In order to determine the pitch of the rafters on a pitched roof, you can use the table:

As can be seen from the table, the rafter step depends on their length and cross section.

Distance between rafters for a gable roof

A gable roof is much more common than a shed roof.

And to explain such popularity is simple: the design is very simple, but for all its simplicity, the gable roof is distinguished by its reliability.

Its design is easy to adjust to any climatic conditions and any roofing material.

When calculating the pitch of the rafters of a gable roof, everything is performed according to the general calculation system (see above).

If the slopes have the same length, then it is enough to perform calculations for one slope.

If the slopes are of different lengths, then the calculation is performed for each slope.

It should be remembered that the limit values ​​\u200b\u200bof 70 and 120 cm.

What is the step depending on the material of the roof

Ondulin

If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and not more than 90 cm from each other.

A crate of timber with a section of 40 x 50 mm is laid on top.

metal tile

Roofing from metal tiles is most often used in the construction of country houses.

Because this material is much lighter than ceramic or cement tiles.

Although in appearance it is very similar to her.

A small one makes it possible to use boards of a smaller section when creating a truss system, and use thinner bars for the crate.

Reducing the size of the elements of the rafter leg system, in turn, reduces the load on the walls of the building and its foundation.

During the construction of the rafter system under the metal tile, the rafters are mounted in increments of 60 - 95 cm.

The cross section of the material is 50 x 150 mm.

According to experts, if a heater having a thickness of 150 mm is placed between the rafters, then the most comfortable living conditions will be created in the attic.

To ensure ventilation of the space where the insulation is laid, when installing the rafter system, holes will be drilled near the upper roof with a diameter of 12 mm.

The technology for manufacturing a truss system for metal tiles does not differ significantly from the technology for manufacturing a frame for other roofing materials.

Its only difference is the installation at the top.

The upper support is mounted not on the side of the ridge beam, but on the ridge run.

The presence of a free zone between the rafters allows the air to fully circulate under the flooring, which helps to protect against the formation of condensate.

Ceramic tiles

The design of the system for ceramic tiles has its own characteristics.

After all, clay is used to make such a roofing material.

And this is very heavy material.

If we compare metal and ceramic tiles, the latter weighs 10 times more.

Accordingly, the truss system is significantly different.

On 1 square meter of the roof surface there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.

The rafters for such a frame system are made from wood that has been dried for a long time.

Such wood should have a moisture content of no more than 15%.

A beam with a section of 50 x 150 or 60 x 180 mm is used.

So more reliable.

And the distance between can be 80 - 130 cm.

The exact value can be called if the angle of inclination of the slopes is known.

If the angle of inclination is 15 degrees, then the pitch of the rafters will be 80 cm.

And if the angle of inclination, for example, is 75 degrees, then the step can be larger - 130 cm.

More than 130 cm interval between the rafters do not.

Also, when calculating the pitch of the rafters, their length is taken into account.

The larger the dyne, the smaller the distance between them.

The shorter the rafter legs, the greater the distance can be.

If the angle of inclination is 45 degrees, then the roofer can safely move along the roof if the pitch of the rafters is 80 cm.

Decking

When creating a rafter system for corrugated board, the minimum distance between is 60 cm.

The maximum value is 90 cm.

If for some reason the pitch of the rafters was more than 90 cm, then it becomes necessary to install large cross-section boards.

The rafter legs themselves can have a section of 50 x 100 or 50 x 150 mm.

Slate

Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.

If it is planned to lay slate on the roof, then the rafters should have a section of 50 x 100 or 50 x 150 mm.

The distance between them is made not less than 60 and not more than 80 cm.

The crate is made from a bar having a section of 50 x 50 mm or a board with a section of 25 x 100 mm.

When constructing any building structure, it should be remembered that there are still unforeseen situations.

And, therefore, at and distances between them, it is necessary to provide a margin of safety.

Video about the installation of the truss system.

It is pointless to argue about the importance of the roof for any building. Not without reason, in the entire history of mankind, more than a dozen different types of roofs have been invented, from simple to quite complex in design and construction. An important element in planning the construction of a roof is the step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.

The distance between the base of the roof slopes is not a constant value and depends on the following components:

• type of roof;
• slope angle;
• the type of roofing material to be installed;
• rafter section dimensions.

Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed by determining the optimal distance between the rafters.

Gable roof rafter pitch

The most widespread in our country are gable roofs. They are a structure that has two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.

With an insufficient slope of the gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the slope angle in regions with a predominance of strong winds is also fraught with a high load and the risk of breaking not only the roof, but the entire structure as a whole.

Mansard roof truss system

Most private houses have an exploited under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. As a rule, the slopes of the mansard roof are broken, having a varying angle of slope. For their installation, a double truss system is used.

The steepness of the lower slopes of the mansard roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. The upper ridge slopes are recommended to be mounted with a reduced gap from each other.

Rafters in a shed roof

For outbuildings and some private houses, roofs with one slope are used. Due to the limited angle of inclination, high pressure is exerted on them. Experts recommend using lumber of increased cross-section for the rafters of a single-pitched roof, with the installation of a minimum step from each other.

When calculating the distances at which roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic is of great importance. Roofing material for such roofs is best chosen with a minimum dead weight, which will reduce the bending load.

Hip roof truss system

The hip roof truss system is considered the most difficult in construction. This type is called four-pitched, since the roof is formed not only by side, but also by additional end slopes, where the installation of rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.

Under the hip roof, the attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, vice versa. An additional aspect of the calculation is the roofing material used.

The dependence of the pitch of the rafters on the roofing material

In addition to variable snow and wind loads, a constant (static) one also acts on the roof, the force of which depends on the roofing material used. It is no secret that different types of roofs have their own weight, which can differ by 10 or more times.

The right choice of material affects not only the top, but also all other parts of the structure of a residential building and other buildings. Not without reason, when designing the foundation, it is necessary to decide in advance on the choice of the roof.

Roofing from profiled sheet

Currently, one of the most common roofing materials is a profiled sheet, which is produced galvanized or followed by a polymer coating. The distinguishing features of the profiled sheet include the following parameters:

1. High corrosion resistance;
2. As a result, a long (more than 15 years) service life;
3. Easy installation even without the necessary qualification;
4. Small sheet weight (weight 1 m 2 is 4-5 kg).

Since this roofing material does not exert a high load on the rafter system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows minimizing the total load on the foundation and walls.

Roofing from a metal tile

The second common type of steel roofing materials is metal tiles. This type of profiled sheet, which successfully imitates natural clay material, but with a lower mass (10 or more). A feature of the rafters under the metal tile is the smaller section size.

When choosing at what distance to install the rafters, first of all, you should be guided by the dynamic load. Like a profiled sheet, a metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch coniferous board. All this makes a metal roof low-cost.

Rafter system for ondulin

In the 21st century, corrugated sheet materials were replaced by a more durable and lightweight analogue - ondulin. Among others - the most lightweight material. The weight of the sheet does not exceed 6 kg.

The small thickness of ondulin sheets at slope angles of less than 15 ° requires the construction of a continuous crate of plywood sheets, for example, which will require an appropriate rafter pitch. This should be taken into account in the calculations.

slate roof

Not so long ago, a wavy material from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today he finds his fans in the construction of various outbuildings.

A high mass, comparable to the weight of a clay tile, will not allow the use of the same truss system as under a metal tile. Building codes define a minimum angle of slope for a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the truss system with the crate exceeds the permissible parameters. The step of the inclined bars, as well as their cross section, are selected individually in each case.

Polycarbonate roof

In recent years, more and more often on the roofs of verandas and gazebos, an artificial polymer material, polycarbonate, has been used. Produced in two versions - monolithic and honeycomb. The first in its properties is similar to ordinary quartz glass, but significantly exceeds it in strength. The second one has less mechanical properties, but high thermal insulation and light transmission.

Cellular polycarbonate is standardly much lighter than a monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ of the width of the sheet of material. The high strength of the monolithic analogue also makes it possible to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semi-circular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.

Thematic material:

Rafters under a soft roof

The original pattern can be obtained through the use of soft roofing materials, which are spread with an adhesive layer. They are installed on a continuous crate made of plywood or OSB. The step of the rafters should allow you to fix the sheets, so it is chosen as a multiple of ½ of the width. Given the standard dimensions of plywood 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.

Rafter step for insulation

The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common plates with dimensions of 600x1000mm. These parameters are used as starting points.

Rafter pitch calculation scheme

According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula, depending on the total length of the roof. For the calculation, you must perform the following list of actions:

1. determine how much distance should be between the rafters for your specific building conditions. According to the reference book, the magnitude of wind and snow loads in the area is determined.
2. the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. If the value is not an integer, it is rounded off.
3. the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.

For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under a metal tile is 0.6 measure. The length is assumed to be 16 meters. Hence:

1. 16:0,6+1=27,66;
2. rounding the result, we get 28 rafters per slope;
3. 16:28 \u003d 0.57 meters - the center gap of the rafter legs for these specific conditions.

As you can see, the calculation technology is not complicated, but this is just an approximate scheme. Taking into account many other parameters mentioned above can make certain adjustments.