So, for the design to serve a long period time, was strong and also reliable, it is worth thinking not only about the foundation, but also about the roof. Construction system such an element plays a huge role, because it is the roof that takes on the negative aspects of the changes weather conditions, as well as other situations.
Rafter system one pitched roof should be characterized certain requirements, among which:
- Rigidity
- Little weight
- High quality material
Such requirements must be taken into account so that the structure lasts a long time.
The rigid characteristics of the element play important role, because it is with the help of rigid elements that the connection occurs various parts. Such elements should not be subject to deformation processes, as well as expansion under any circumstances.
The basis of this design is a triangle, which is made using a special reliable frame. Each element of this frame is fixed to one another in parallel, and with the help of strong fixation the stability of the entire structure is ensured.
Rafter system pitched roof: scheme
But if such frames are poorly attached and movable, this will only lead to negative consequences . Such a roof can collapse not only from strong winds, but also on its own.
If we talk about weight, then this the roof should not be heavy. That is why this system is made, in most cases, from wood. If the weight is large enough, it is necessary to make a supporting base of metal.
There are cases when use coniferous trees, the humidity of which is not less than 18 percent. Among mandatory conditions when using trees, note:
- Antiseptic treatment
- Use of flame retardants
Only in this case, the nodes in the area of which the entire system is precisely fastened will be distinguished by high strength and reliability.
High quality of materials used is one of the main rules. The tree must meet the following characteristics:
- Applies 1-3 different varieties . It is important to pay attention to ensure that there are fewer cracks and knots. Per meter of material, 3 knots with a height of no more than 3 centimeters are allowed. Cracks are also allowed in a minimum amount, but not throughout the entire depth.
- It is advisable to make elements of a load-bearing nature from parts whose thickness is at least 5 cm and whose area is at least 40 m2.
- Boards made from coniferous trees can only be used with a length of no more than 6.5 meters, and from deciduous trees– up to 4.5 m.
- It is advisable to make pillows, purlins, and also the Mauerlat from trees that belong to solid deciduous trees . Such material should be pre-treated with one or another high-quality antiseptic.
Shed roof design
So, before starting to manufacture the system, it is very important to know what its main parts are:
- Mauerlat, which can be called the foundation of the system. Using this part the load is distributed evenly and correctly.
- Run represents an element that confidently fastens all the legs of the rafters. The ridge version is at the top, but here side elements located on the sides.
- The rafter leg is installed to determine the angle of inclination of the slope, as well as for the reliability of the entire roof and its appearance. It is this product that fixes individual parts of the system.
- Tightening helps keep feet in place, do not move apart. This part connects them at the bottom.
- Racks, as well as struts give additional foot stability.
- Lathing It consists of boards, as well as cut beams. It is stuffed perpendicularly, transfers the load to the rafter legs.
- The overhang of the entire roof protects against precipitation.
- Horse is the place where two roof slopes meet. It is along this element that the lathing is packed, due to which it occurs strengthening one or another part of the roof.
- fillies are used when the length of the legs is short, as a result of which they create an overhang.
ATTENTION!
Only by taking into account the described parameters will you get a reliable roof.
A shed roof is characterized by the presence of one slope, which is characterized by an angle of 14 to 26 degrees. In the case when the roof is made for a small house, the span will not exceed 5 cm, so it is recommended to make a layered system.
The support of such a roof is made on external walls, as well as on a wall that exists inside the object. Rafter systems are used in cases of rafter trusses.
Roofing pie, or rather, its design, depends on which final version of the coating will be chosen. But, regardless of the material, this element Maximizes the “life” of the roof, durability.
The lean-to type requires special attention, since it is this stage of construction that has the greatest influence on the climate of the structure.
Rafter system design
Fastening the rafters of a pitched roof
The fastening scheme is quite simple, as it consists of parallel boards that rest on two walls. To install the legs, special transition elements are used, which are made of wood.
Depending on what material is used, the following can be used as a transition piece:
- Mauerlat. In the above single-slope roof system, these are two wooden beams, which lie separately and complete the walls.
- Upper foot, which is made of beams.
- Upper harness the entire frame.
Although the design of this roof is simple, there are some subtleties of fastening the rafters that are important to know about.
The fact is that the nodes that are used must take into account all the negative aspects of a material such as wood.
When designing, the following tasks should be taken into account:
- The ability to easily move wooden parts from one another
- Adaptation to the consequences that may occur after the subsidence of each wall in order to take a stable position
- Excluding everyone possible reasons violation of one or another connection
The triangles are fastened according to the following scheme: the horizontal side is installed on the Mauerlat and fixed. It is very important that it has a sufficiently large area for docking with other elements.
It is important to install the rafter legs at a certain angle to the supporting elements. It is worth understanding that two points are not enough for a strong fastening, so there are methods that are used to avoid negative consequences.
First of all, it is important to increase total area rafter interactions, as well as the supporting part using:
- Select cuts
- File the upper as well as the lower edges of the legs. With these steps you can easily create support platform, increase stability.
Fastening the rafters
Rafter pitch
The distance between the rafters of a pitched roof is calculated depending on what material is chosen, as well as the cross-section. Such calculations should be done at the stage, building standards and rules are used.
The calculation for the above roof option is very simple. There are no racks or braces here; as a result, only the rafters of the pitched roof are taken into account.
Usually, for such a roof, wood material used coniferous species , the moisture factor of which is approximately 20-22 percent. Such boards should be characterized by evenness and the absence of blue.
Each blood material is characterized by its own characteristics, so the pitch of the rafters is also different:
- Using distance depends on sheet size. Typically, the beam spacing is at least 60 cm and up to 90 cm. For larger distances, additional boards with a larger cross-section of 150 mm are used. It is important to take into account the use of lathing, the cross-section of which should be 30*100 mm, and installation is carried out taking into account a span of at least 50 cm.
- often used, but its weight is taken into account. Beams for such a system are pre-dried. When determining the step size, the length of the boards should be taken into account. At maximum length worth doing minimum distance between the rafters. The same rule is used with a minimum length of beams - a large step distance. Typically, 80 cm is considered a safe step.
- Under, which is used much more often than the two above materials, beams with a small cross-section are used. The step in this case is equal to a number from 60 to 90 centimeters. Timber should be used with a cross section of about 50*150 mm.
- Using it is worth understanding that this in the form of sheets. Beams should be placed with a distance that will not be less than 60 centimeters, but not more than 90 centimeters. The cross-section of the timber is 50*200, and 50*150 mm can also be used. When using a smaller cross section one can expect negative aspects, since such a cross-section will not be able to provide high strength to the legs.
- Under , which is used very rarely, rafter legs with a section of 50*100.50*150 are used. The pitch is no less than 60 centimeters, and no more than 80. In this case, the pitch differs depending on the roof structure.
Rafter pitch table
Installation of the rafter system
When deciding to install the rafters of a pitched roof yourself, you should first prepare all the elements and also treat them with special means.
The boards should be laid on both sides of a certain roof and placed in the grooves.
Only after this is it important to attach several outer rafters.
CAREFULLY!
Please note that it is important to hammer one or two nails into each joint. The legs are installed taking into account the previously stretched strings, after which they are nailed in the same way. After this, the sheathing is installed, and the roof is laid.
After calculation and design, there are certain stages of installation:
- Installation of supporting beam. Big beam laid along the wall of the object. It should first be planed and soaked in antiseptic.. It is important to lay roofing felt at the end of the wall; mount the timber on it level using anchor bolts.
- Processing of timber and rafter elements. The board is planned to extend above the roof overhang - a level of about 40 cm on each side, depending on. It is important to consider that the steeper the angle, the less it costs to make an overhang. When using metal tiles and corrugated sheets, the step is 120 centimeters. In cases where the width is more than 6 meters, it is recommended to reduce the step to 1 meter. The board is embedded into the Mauerlat for strength.In contact with
A gable roof is one of the most common and versatile roofing structures for buildings for various purposes. They can be made either cold for non-residential attic spaces or insulated for attic rooms.
Important. The house has two main architectural elements that play a decisive role in the durability and safety of operation: the foundation and the roof. During their design, it is necessary to strictly comply with all the requirements of building codes and regulations.
Only professionals can design and build a rafter system. They must have deep theoretical knowledge and extensive practical experience in performing similar works, only practice allows you to accept optimal solutions during construction.
Each house has its own individual characteristics, each batch of lumber differs in strength, each load-bearing unit can be manufactured and fixed different ways. All this affects the stability of the rafter system, increases or decreases the estimated cost of the roof, etc. It is necessary to achieve such an option so that the rafter system is as simple as possible to construct and at the same time reliable and cheap.
There are many different opinions from inexperienced developers about how to choose the distance between the rafters. Some seriously give advice on choosing this parameter for each type of roofing material: natural or artificial piece tiles, metal tiles and corrugated sheets, soft bitumen or slate coverings. In fact, none of this is true; architects never put this in the initial data when calculating the pitch rafter system type of roof.
Physical properties roofing materials, together with other factors, influence not the distance between the rafters, but their dimensions and additional structural elements of the rafter system to increase the stability of the structure, including:
- vertical supports;
- horizontal purlins;
- corner supports;
- crossbars and other special elements.
In the roof structure wooden house a bunch of various elements, each of which performs its own function and is fixed in a certain way. To find out in detail what elements the roof of a wooden house consists of,. You will find not only descriptions of the elements, but also the best practical tips!
Before starting calculations, engineers have initial data (technical specifications) for the entire system; taking these values into account, other parameters are calculated. The initial data also includes the pitch of the rafters; it is known before the start of design and does not change in the final project. What exactly affects this parameter?
Factors affecting the distance between rafters Short description 
This factor has an effect only if it is planned to make the roof insulated. The design specifications must indicate the type and dimensions of insulation used, but they vary. Eg, standard width foam and pressed mineral wool is 60 cm. In order to eliminate the formation of cold bridges, facilitate and speed up the process of installing insulation and minimize the amount of unproductive waste, the span between the rafters should be within 56–58 cm. Roll mineral wool can have a width from 120 cm to 100 cm. Accordingly, their installation requires a different pitch of the rafter legs.
The greater the distance, the more load each rafter leg takes. This affects its size and the total amount of lumber for the roof. Currently, wood belongs to a very expensive category of building materials; it is necessary to reduce consumption. This is done both by using additional supports of the rafter system for optimal load distribution, and by adjusting the number of rafter legs, which allows you to reduce the cross-section of the roof elements and save expensive boards. 
Each house has its own architectural features. This refers to the location and number of chimneys and ventilation outlets, the layout of attic spaces, manufacturing materials load-bearing walls, the presence of a wooden Mauerlat or concrete reinforcing belt. Rafters cannot be located above chimneys and ventilation pipes and interfere with installation skylights etc. Such nuances must be thought through during the design of the structure; they also affect the distance between the rafters. Important. The pitch of the rafter legs is measured between the axes; when choosing the final parameter, you need to take into account the thickness of the boards. For installation of insulation important has a distance between the side planes, and not the axes of the rafters.
What effect does the type of roofing material have on the spacing of the rafters?
This issue needs to be discussed in detail; quite a few developers do not fully understand the problem. To answer you need to know fundamental differences materials and their influence on the distance and calculation of rafters. We emphasize that we do not mean operational characteristics roofing coverings or their designer look, namely structural and physical differences.
- Linear dimensions. The largest sizes are metal coatings, can reach eight meters.
All these materials have fundamentally different methods fixation to the rafter system. But they do not have any effect on the pitch of the rafters.
- Flexural strength. There is a misconception that for flexible roofing materials you need to reduce the pitch, this is not so. Not a single roofing covering is fixed directly to the rafters; for this purpose, a sheathing is made, and when arranging it, the methods of fastening are taken into account. Moreover, for some types of roofing coverings it is necessary to control them very precisely - the materials have precisely specified fixation points during manufacturing.
- Weight. The calculation of the rafter system is influenced only by heavy coatings: piece tiles and asbestos-cement slate. All other types of roofs have such insignificant mass that it is not taken into account when designing the structure.
Prices for different types of tiles
Roof tiles
Algorithm for calculating the rafter system
As mentioned above, the distance between the rafters is set to initial stage and depends on the characteristics of the insulation. They influence another one of them important parameter– width of the boards.
She must take into account minimum thickness insulation layer taking into account the climatic zone of the building's location. If in cold regions the insulation should have a thickness of 20 cm or more, then for warmer climates 10 cm of insulation is sufficient. Accordingly, the width of the rafter board is from 20 cm to 10 cm.
Practical advice. You always need to consider the cost of lumber. There are options when it is much more profitable for the rafter legs to use boards 10 cm wide, and increase the depth of the niche for the insulation by adding ordinary thin low-quality ones. But in all cases, the main sizing criterion is the ability to support maximum design loads.
The calculation of rafters is carried out in several stages.
Determination of forces on the roof
Several types of loads act on the roof slope, they have different meaning and its characteristics of influence on the strength of the system.
- Constant loads. Meaning weight building materials for the rafter system and the mass of roofing coverings. If heavy types of materials are used as coatings, then their weight must be taken into account.
For lightweight metal sheets, this is not necessary.
The fact is that the roof is a particularly important structural element of the building, and they have a safety margin of at least 140%. This means that the structure can withstand loads almost one and a half times greater than the calculated ones. The maximum load on the roof is created by snow and wind. The values of these forces are measured in hundreds of kilograms, and the mass of metal sheets is only a few kilograms per square meter. The safety factor completely covers the possible increase in effort.
- Variable loads. These include snow and wind forces; they are placed in tables available in building codes and regulations. This takes into account the location of the building (in the city or in an open area), number of storeys, roof shape, etc. It must be borne in mind that in Lately The climate is changing rapidly, and the data in the tables is fifty years old. It is not very correct to use them; it is better to take data from the reports of the hydrometeorological center of your region.
The maximum permanent and temporary loads are summed up and increased by approximately 40% to create a safety margin for all load-bearing elements. The safety factor can be taken into account using another method. After all engineering calculations have been completed, the linear parameters of the rafters are determined, in the final version they are multiplied by a factor of 1.4, the results are used when creating working drawings of the rafter system. It doesn’t matter which method you use, the main thing is to maintain the accuracy of mathematical calculations, and only a specialist with a special technical education can perform them.
The methodology is prescribed in SNiP 2.01.07-85, it includes changes to some formulas adopted in 2008. Before taking into account the distance between the rafters, you should find out all the loads acting on them.
Snow loads
Prices for snow guards
Snow guard
Engineers use the formula
Formula 1. Determination of snow load
We have already mentioned that the normative load may differ significantly from the actual load, and therefore it is recommended to use more up-to-date data. As for the roof inclination angle α, this parameter is set in the original technical conditions for the design of the rafter system. The coefficient µ is determined by the formula
Formula 2. Definition of µ
One component of several forces on the rafters has been determined; now we should move on to the remaining types of loads.
Important. Please note that snow loads, depending on the climatic region, range from 120–180 kg/m2. Now it should be clear why the weight of light roofs can be ignored; their forces are approximately 5–7 kg/m2, this is within the limits of mathematical error. In addition, a safety factor is applied. 40% of 180 kg is 72 kg, this value is much greater than the mass of metal roofs and is already taken into account when calculating the strength of rafters.
Wind loads
These forces can reach significant values and are necessarily taken into account when calculating the parameters of the rafter legs. In this case, two types of wind loads are distinguished. When the slopes are tilted more than 30°, the wind tries to overturn them and puts great force on the leeward side of the roof. If the slope is small, then due to differences in the speed of air flow, a lifting force appears, tearing the roof away from the mauerlat. Wind loads are determined by the formula
The wind pressure coefficient by height includes several factors. All of them have complex calculation methods, which are performed by competent thermodynamic engineers.
To facilitate calculations, there is a ready-made table in the regulatory documents; the specific coefficient is selected depending on:
- building height;
- type of terrain (open or closed);
- heights of urban buildings.
The aerodynamic coefficient can be greater than one or less than one. In the first case, the wind load increases, in the second it decreases slightly. For most buildings, simplified calculations are made for wind loads; it is assumed that the coefficient is 0.8.
Weight of rafter system and roof elements
Taking into account the characteristics of the lathing and the materials used to make the rafter legs, their total mass can increase the load on the system within the range of 30–50 kg/m2. As already mentioned, this parameter can be ignored. The large safety factor makes the roofs universal; they can be covered with any type of roofing materials.
Calculation of rafter legs
The distance between them is included in the design specifications, is a stable value and is specified in the design specifications. Next, you should find out the linear dimensions of the rafters so that they can withstand the maximum possible forces during operation. Distributed load on linear meter legs is determined by the formula
We have all the initial data for calculating the distributed load.
Now you can proceed to the selection optimal cross section rafter leg. In this case, you should be guided by the GOST 24454-80 table, which indicates the standard dimensions of lumber (thickness and width).
Nominal dimensions of thickness and width of edged lumber with parallel edges and thickness of unedged and edged lumber with non-parallel edges
You should definitely familiarize yourself with the table; this is necessary to understand the methodology for selecting boards. For example, with a thickness of 16 mm, the maximum width of the board is 150 mm, and with a thickness of 75 mm, the maximum width increases to 275 mm.
You need to set the section width of the board and, taking this parameter into account, calculate the height. The formula used is
It is suitable for cases where the roof slope is α< 30°.
If the slope angle α > 30°, then you need to use the formula
- H– the required height of the rafter board;
- Lmax– the distance between the most distant points of the rafter support. For small slopes it is equal to the distance from the ridge to the Mauerlat; in other cases it is necessary to install various types stops and measure the distance taking into account their location;
- Qr– distributed load on the rafter leg, it was calculated earlier;
- B– board thickness, selected arbitrarily, taking into account individual characteristics rafter system;
- Rizg– standard indicators of wood bending resistance.
They depend on the quality of lumber and the type of wood; they are taken from tables of state standards. The quality of lumber plays a decisive role in the bending resistance of lumber.
For example, if for the first grade of pine Rben = 140 kg/cm2, then for the third grade this parameter is reduced to 85 kg/cm2. Standards strictly regulate the bending radius of the roof; if it is too small, then there is a high risk of leaks due to damage to the integrity of the roof coverings. For all roof elements, the deflection value cannot exceed L (length of the working section)/200.
SNiP has a formula for checking the condition under which the deflection does not exceed the established standards
If the amount exceeds one, then it is necessary to increase the thickness or width of the rafter leg.
Calculation example
The number of rafters is known; this value is always determined taking into account the required distance between them. In our case, the pitch is 80 cm, the slope angle is 35°, the length of the working section is 280 cm. The rafter system is made of pine, the bending radius of this first-grade material is 140 kg/cm2. Piece cement-sand tiles will be used as roofing material. This is a very heavy material, its weight is recommended to be taken into account. The weight of a square meter of tiles reaches 50 kg. Now all the initial data are known, you can begin the calculations.
Taking into account the climatic zone, the total wind and snow load is 253 kg/m2, to which the weight of the tiles should be added, the total is 303 kg/m2. The distributed load on the rafter is calculated using the formula and in our case is 242 kg/m2. It is planned to make the rafters 5 cm thick; you need to find their width.
Apply the formula
This particular formula is used due to the fact that the angle of inclination of the slope is more than thirty degrees. Now it remains to check whether the maximum permissible deflection radius of the rafter will not be exceeded. If the value is less than one, everything is normal. If it is more than one, then it is necessary to increase the linear dimensions of the boards.
Prices for timber
When to calculate the distance between rafter legs
This need arises very rarely and mainly concerns non-residential premises. For example, a developer already has boards for making a rafter system; he needs to know at what distance to fix the rafters so that the roof can withstand the design loads. That is, you need to do the reverse calculation. If in a standard situation the distance is known and the dimensions of the boards are selected taking these parameters into account, then in the second case the opposite is true. The dimensions of the rafter boards are known; the pitch of the rafters needs to be determined. This is done in this order.
Knowing the total load on the roof and the maximum load on one rafter by simple arithmetic operation determine the number of rafter legs. Of course, all roundings are made upward; an excess safety margin will never harm the rafter system. Final stage– the length of the roof slope is divided by the minimum number of rafters and the distance between them is obtained. Rounding should be done in the direction of decreasing the step.
Video - Selecting the distance between rafters
The roofs of modern private houses can have different configurations. The most popular type of roofing is gable. The undoubted advantages of such a roof are the owners suburban areas they consider reliability to be quite attractive appearance and efficiency. The design of this type of roof is extremely simple, and therefore it will not be difficult to erect it, even with your own hands.
Light and durable sheet materials are what is most often used to cover a gable roof. Corrugated sheeting, for example, is simply ideal for such a design. This type of roof protects well inner space at home, lasts a long time and is inexpensive. Of course, the procedure for constructing a rafter system under corrugated sheets, like under any other material, has some of its own characteristics.
Where to begin
How is a gable roof assembled? under the corrugated sheeting it will turn out to be reliable, and the roof itself will be neat only if it is first prepared detailed project designs. When developing the latter you need:
determine the angle of inclination of the slopes;
decide on the type of materials needed for construction;
make detailed drawings of the frame indicating the method of connecting all nodes.
If all these operations are completed without errors, the end result will be a strong gable roof. A rafter system for corrugated sheets, a drawing of which can be made using, for example, special software on a computer, will last as long as possible.
Load calculation
This step should never be skipped when drawing up a roof project. Correctly performed calculations are the key to the end result being a durable gable roof. The rafter system for corrugated sheeting (a photo of the assembly of such a frame can be seen below) is mounted taking into account the following parameters:
weights of all materials used;
The values of the last two indicators can be found in special tables developed specifically for each specific region.
All figures obtained as a result of calculations must be added and multiplied by a reliability factor of 1.1. Having calculated the rafter system of a gable roof in this way, it will be possible to determine, first of all, the type of materials required for assembly. Also, taking into account the final load indicator, the optimal angle for the roof frame supports is selected.
Slope angle
In addition to the load, when choosing this indicator, the characteristics of the roofing material itself should also be taken into account. The angle of inclination of the slopes can be any, but not less than 12 degrees. If you make the roof flatter, it will leak in the future. At the same time, the sheets themselves will begin to sag under the weight of snow in winter. That is, the roof will have to be constantly repaired. And this, of course, is additional costs.
IN Middle lane In Russia, taking into account wind and snow loads, it is almost universally allowed to erect roofs with slope angles of 30-45 degrees. This option is ideal for corrugated sheets. In the southern regions, the angle of inclination of the slopes of the roofs of houses may be smaller, and in the northern regions, on the contrary, it can be greater.
Among other things, when choosing a method for installing rafters, it is worth considering exactly how the attic will be used in the future. If it is intended to be insulated and equipped as a living space, it is better to make the slopes steeper. But of course, in this case, building a roof will cost a little more, since more materials will have to be used.
What to build from
What specific materials can such a gable roof be constructed from? with your own hands - in any case, it is a responsible matter, and must, of course, be as reliable as possible. But one of the advantages of corrugated sheeting is that it is light in weight. Therefore, it is not necessary to use any special, very durable materials to assemble the frame for it. This type of roof is quite suitable for rafters standard timber 150x100 mm. It is advisable to use lumber of a larger cross-section only if the attic is intended to be used as a living space. Rafters for such a roof are usually made of 200x100 mm timber.
The sheathing can be assembled from edged boards 30x100-150 mm. Lumber that is too wide in this case cannot be used. After some time, such boards will simply dry out and become severely warped, which will have an extremely negative impact on the reliability of the roof. Under the Mauerlat it is better to take a thicker beam - 200x150 mm.
Step between structural elements
Too often frame supports under the lungs metal sheets installation is also optional. The optimal distance between the rafters of a gable roof under corrugated sheeting is 60-80 cm. As for the sheathing, the pitch between its elements is selected taking into account the type of sheets used. So, for thick material 0.6-0.7 mm with a profile height of 3.5 cm, boards can be stacked at a distance of up to 1.5 m from each other.
For standard N-grade corrugated sheeting, the lathing pitch is usually 60-70 cm. The same distance is suitable for CH material. Thin sheet C is mounted on a sheathing, stuffed in increments of 10 cm or on a sheathing made of 12 mm plywood or OSB sheets.
How to assemble a gable roof. Rafter system for corrugated sheets
The roof frame of the house is mounted in several steps:
Mauerlat is installed;
rafters are installed;
if necessary, insulation is installed;
the rafters are covered with waterproofing;
the sheathing is stuffed.
Mauerlat installation
They begin assembling such a structure as a gable roof made of corrugated sheets with their own hands by installing this particular element. The Mauerlat is mounted on top of the building frame. As a basis for the rafter system, this element is used only on brick, monolithic or block walls. In cobblestone and chopped ones, its role is played by the upper crown. The timber should be secured to the walls using anchor bolts. You can also use steel dowels, galvanized wire with a thickness of 5 mm or staples.
Methods of fastening rafters
The supports themselves can be attached to the Mauerlat in two ways. For brick, block and monolithic houses Rigid fixation technology is used. In this case, they are attached to the Mauerlat using galvanized steel corners and self-tapping screws or a “knot” of three nails (one in the upper plane, two on the sides).
On chopped and cobblestone walls, the rafters are fastened using the sliding method. The fact is that such houses shrink strongly during the first time after construction. Therefore, a rigidly fixed roof frame can simply fail in the future. With the sliding method of installing rafters, special fixing elements, “sleds,” are used, ensuring the mobility of the supports in a small range.
How to install
The supporting elements of the frame must be installed correctly. In this case, you will get a neat symmetrical gable roof. The rafter system for corrugated sheeting, like for any other material, must be assembled using a template. In this case, all legs will have the same length. For gable roofs, corrugated sheets can be used as simple straight rafters (with a cut under required angle edge), and the option with mounting sockets for the Mauerlat. The frame supports are usually attached to each other at the top using special thick steel plates.
The end trusses are always installed first. Next, a cord is stretched between their highest points. Then, focusing on it, intermediate trusses are installed. On large roofs between the outer paired rafters it is pre-installed ridge run on supports. The latter are securely fixed to the floor beams.
Installation of insulation and waterproofing
If the attic is intended to be made habitable, it will, of course, have to be insulated during the construction of the roof. On corrugated roofs, mineral wool is most often used for this purpose. To support it, a wire is stretched from the attic side onto the rafters. The mats themselves are installed by surprise.
The waterproofing is sewn onto the rafters with a slight sag (2 cm). Do not stretch the film too much. Otherwise, when the frame moves, it may simply tear. The waterproofing strips are installed horizontally from bottom to top with an overlap of at least 10-15 cm.
Installation of sheathing
The support boards under the corrugated sheets are attached to the rafters using nails with a diameter of about 3-3.5 mm. The length of the fasteners must be twice as long as the thickness of the elements being fixed. Assembly begins from the cornice. The boards should be fastened to each rafter with two nails. Two last row at the ridge they are stuffed without a gap.
After the sheathing has been assembled, you can begin covering the frame with the corrugated sheet itself. At the final stage, the roof gables are covered with boards.
What you need to know
Wood is a material that is very easy to process and at the same time quite durable. That is why the rafter system of a gable roof is most often assembled with your own hands from timber and boards. However, unfortunately, lumber cannot boast of a very long service life. Sooner or later, the roof of the building begins to dry out or rot. Therefore, before assembling it, the timber and boards must be processed special compounds, increasing their moisture resistance.
Another disadvantage of wood is flammability. To reduce the risk of fire to a minimum, the lumber used to construct the building frame should, among other things, be carefully treated with a product that increases its fire resistance.
This is how the gable roof is assembled. The rafter system under the corrugated sheet, as you can see, is mounted simply. Nevertheless, installing a roof frame is a very responsible undertaking. If any technology is violated, the owners of the house will inevitably have problems with leaks and the need for replacement. individual elements etc. Therefore, it is worth approaching the assembly of the roof truss system with maximum responsibility.
There is no point in arguing about the importance of a roof for any building. It is not for nothing that over 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 When planning the construction of a roof, there is a 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 sizes.
Before starting the process of erecting the upper structure of the house, you should perform a calculation, determining the optimal distance between the rafters.
Gable roof rafter spacing
Gable roofs are most widespread in our country. They are a design that has two parallel to the plane, with an inclination angle relative to the horizon from 20 to 50 degrees.
If the roof slope of a gable roof is insufficient in snowy areas, there is a risk of accumulation of large snow masses, which can lead to the destruction of the structure. Increasing the slope angle in regions with predominant strong winds It is also fraught with high loads and the danger of breaking not only the roof, but the entire structure as a whole.
Mansard roof rafter system
Most private houses have a usable 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, stingrays mansard roof broken lines with varying slope angles. For their installation, a double rafter system is used.
The steepness of the lower slopes of the attic roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not large. Thanks to this, the rafters in the lower part can be installed with maximum step. It is recommended to install the upper ridge slopes with a reduced gap from each other.
Rafters in a pitched roof
For outbuildings And some private houses use roofs that have one slope. Due to the limitation of the angle of inclination, they are exposed to high pressure. Experts recommend using lumber with a larger cross-section for the rafters of a pitched roof, setting a minimum spacing from each other.
When calculating the distances at which roof beams are installed, Special attention should be given to the magnitude of the snow load in a particular area. With a small slope, this characteristic is of great importance. It is better to choose roofing material for such roofs with a minimum dead weight, which will reduce the bending load.
Hip roof rafter system
The hip roof rafter system is considered the most complex in construction. This type is called hipped, since the roof is formed not only by side, but also by additional end slopes, where the rafters are installed not on the ridge, but on the corner strings. This places special demands on the organization of the roof frame.
Under hip roof An attic is not often installed. This is due to the small angle of inclination of the rafters and the roof as a whole. If the angle of the slopes to the horizon increases, the distance between the rafters increases; if it decreases, vice versa. An additional aspect of the calculation is the roofing material used.
Dependence of rafter pitch on roofing material
In addition to snow and wind loads, which are variable, the roof is also subject to constant (static) loads, the force of which depends on the roofing material used. It's no secret that different kinds roofs have their own mass, which can differ by 10 or more times.
The correct choice of material affects not only the upper, but also all other parts of the structure of a residential building and other buildings. It is not without reason that when designing the foundation it is necessary to decide in advance on the choice of roof.
Corrugated sheet roofing
Currently, one of the most common roofing materials is profiled sheet, produced galvanized or with subsequent polymer coating. TO distinctive features profiled sheet will include the following parameters:
- High corrosion resistance;
- As a result, a long (more than 15 years) service life;
- Easy installation even without the necessary qualifications;
- Low leaf mass (weight of 1 m2 is 4-5 kg).
Since this roofing material does not place a high load on the rafter system, the distance between the elements is selected as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof sheathing. All this together allows us to minimize the overall load on the foundation and walls.
Metal roofing
The second common type of steel roofing materials is metal tiles. This type of profiled sheet successfully imitates natural clay material, but with less mass (10 or more). A special feature of rafters for metal tiles is their smaller cross-sectional size.
When choosing at what distance to install the rafters, you should first of all be guided by the dynamic load. Like corrugated sheets, metal tiles are not demanding on the size of the rafters and can be easily mounted on a sheathing made of one-inch softwood boards. All this does metal roofing low-cost.
Rafter system for ondulin
In the 21st century, wavy ones are replacing sheet materials a more durable and lighter analog has arrived - ondulin. Among others, it is the lightest material. The weight of the sheet does not exceed 6 kg.
The small thickness of ondulin sheets with slope angles of less than 15° requires the construction of a continuous sheathing made of plywood sheets, for example, which will require an appropriate spacing of the rafters. This should be taken into account when making calculations.
Slate roofing
Not so long ago, a wavy material made from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today it finds its fans in the construction of various outbuildings.
High mass comparable to weight clay tiles will not allow using the same rafter system as for metal tiles. Building codes determine the minimum slope angle of a slate roof to be 22 degrees or more. Otherwise, the load from the material itself and the rafter system with sheathing exceeds the permissible parameters. The pitch of the inclined beams, as well as their cross-section, are selected individually in each specific case.
Polycarbonate on the roof
In recent years, artificial wood has increasingly been used on the roofs of verandas and gazebos. polymer material– polycarbonate. Available in two versions - monolithic and cellular. The first is similar in properties to ordinary quartz glass, but significantly exceeds it in strength. The second has smaller mechanical properties, but with high thermal insulation and light transmittance.
Cellular polycarbonate is usually much lighter than its monolithic counterpart. It is used as a roof without the use of lathing, provided that the pitch does not exceed ½ the width of the sheet of material. The high strength of the monolithic analogue also allows you to avoid transverse rafters elements. Sufficient flexibility allows you to cover semicircular roofs on metal frame, the step of which does not exceed 0.9 meters.
Thematic material:
Rafters for soft roofing
An original pattern can be obtained through the use of soft roofing materials, spread with an adhesive layer. They are installed on a continuous sheathing made of plywood or OSB. The pitch of the rafters should allow the sheets to be secured, so it is chosen as a multiple of ½ the width. Provided the standard plywood dimensions are 1520x1520 mm, the center distance between the rafters will be equal to: 1520:3 = 506 mm.
Rafter spacing 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 slabs with dimensions are 600x1000mm. We use these parameters as starting points.
Scheme for calculating rafter pitch
By building regulations The pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed using a simple formula depending on the total length of the roof. To calculate, you need to perform the following list of actions:
- determine what distance should be between the rafters for your specific construction conditions. The reference book determines the magnitude of wind and snow loads in the area.
- The length of the roof is divided by the desired distance, adding one. The result obtained will be equal to the number of rafter legs that are installed on one roof slope. If the value is not a whole number, it is rounded.
- The length of the roof is divided by the number of rafters calculated above, we get the final pitch in meters.
For example, with a slope slope of 30 degrees, the maximum distance between the rafters of a gable roof under metal tiles is 0.6 measures. The length is assumed to be 16 meters. Hence:
- 16:0,6+1=27,66;
- rounding the result, we get 28 rafters per slope;
- 16:28 = 0.57 meters - the center distance of the rafter legs for these specific conditions.
As you can see, the calculation technology is not complicated, but this is just an approximate diagram. Taking into account many of the other parameters mentioned above can make certain adjustments.
Rafter system, undoubtedly, is the most important structural element of 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:
- fastening strength rafters to the ridge and mauerlat;
- correct calculation of the supporting structure for rafters depending on the span length;
- choice rafter material;
- 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 the calculation maximum load on the roof, 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:
- Measure the length of the roof from end to end.
- Received distance divide by maximum size step.
- Round the resulting value to a higher integer. This is the number of rafter spans.
- Divide the total length of the roof by the number of spans. This is the required rafter pitch size.
- Add one to the number of spans.This is the required number of 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 length 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 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. Approximate step between rafter legs 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.