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:
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 materials, but when building 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, take into account the total load, roof structure and used on rafter legs material.
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 roofing materials, which must be taken into account when designing the truss 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 in essence, it is a less rigid and lighter decorative version of corrugated sheeting, therefore the requirements for the rafter system, in particular for the recommended sections of rafter legs, largely coincide.
Features of the rafter structure for metal tiles can be called a significant reduction in the pitch of the sheathing, which should be equal to the length of the longitudinal wave (30 cm for most types). This leads to the need to reduce the distance between the rafters up to 0.6 – 1 m, to reduce the cost of lumber for sheathing. The angle of the roof slope is selected from 22 to 45 degrees.
Rafter structure for ondulin
Ondulin– slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:
- permissible installation angle – 5 – 45 degrees;
- distance between rafters – 60 cm at an angle of up to 15 degrees, up to 90 cm at an angle of more than 15 degrees;
- sheathing - solid plywood on a slope up to 10 degrees, board 30x100 mm in increments 45 cm on the slope 10 – 15 degrees, timber 40x50 mm in increments 60 cm on the slope above 15 degrees.
Considering the light weight of the material, the cross-section of the rafter legs is selected based on the same recommendations as for corrugated sheeting.
Rafter structure for slate covering
Slate- a traditional, fairly rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change recommendations for optimal device 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 universal step battens – 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 standard length sheet 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 length span – less than 6 m(For wooden rafters). Optimal angle – 15 – 20 degrees.
Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where wind pressure is comparable to the snow load, correct installation pitched roof“downwind” can lead to self-cleaning of the roof.
Gable roof is a system of parallel triangles connected to each other by a mauerlat and a ridge. There are many elements for firmly fastening the sides of the triangle together and transferring loads from the rafter legs to the walls - racks, couplers, jibs, support beams and so on.
The step between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. The approximate step between the rafter legs is 1-1.2 meters
Strength of a rigid triangle increases as its shape approaches an isosceles one, therefore, with increasing slope angle up to 60 degrees you can expand the spacing between the rafters.
However, this will also lead to an increase in material consumption and to a multiple increase in the roof windage. The optimal slope angle for snowy regions is 45 degrees, for windy people – 20 degrees.
Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofs step rafters should be from 60 cm to 1 m.
- The correct fastening of the rafters is no less important than the correct calculation of the structure. Before self-installation roofing, it’s worth taking a lesson from an experienced carpenter and reading educational literature.
- When choosing the pitch of the rafters, do not forget about thermal insulation. All types of insulation can shrink a little, so you can buy them by approximate size. The most commonly produced sizes are 60, 80, 100, 120 cm.
- For roofs with a slope of 45 degrees or more, the weight of a person on the roof can be ignored. This removes 175 kilograms of the design load on square meter and allows you to install rafters 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.
As you know, the roof of any building is its upper part, which can combine protective and decorative functions. The roof protects mainly from atmospheric precipitation entering the building from above, while at the same time it can emphasize the appearance, material and color of the roof architectural feature building.
The wooden beams that make up the rigid frame of the roof are called rafters; the selected roofing material is already mounted directly on them.
Just as buildings contain different functional contents (for example, residential buildings or industrial and technological buildings), so do roofs various buildings differ from each other. Their shape can directly depend on climatic conditions: wind load or the amount of snow falling. It is difficult to clean the roof from the latter if its slope is 30 0 or less, and the large “windage” of a high roof can be a serious problem with wind gusts of more than 18 m/sec.
Among the huge variety of roofs, most usually consist of a roof and a set of building structures that support this roof.
One of the main elements of these structures are, as a rule, wooden beams on which the roofing covering is mounted. These beams are called rafters or trusses. They are also the elements of rigidity that determine mechanical strength roof, as well as those guides that determine the angle of inclination roofing covering.
The rafters can be located either from one to the other outer wall building, with a certain slope, or from the center (ridge) of the roof to the outer wall.
According to the first method, single-pitched roofs are installed, and according to the second, gable roofs. It can be assumed that what closer friend
these rafter trusses will be located next to each other, the more reliable the base for the roofing will be.
However, excessive use of materials makes the structure heavier and leads to higher construction costs. Therefore, the question of how to install rafters is one of the fundamental ones when designing a roof.
There are two types of rafters: the so-called “hanging” ones, which rest with their ends only on the external load-bearing walls, and those which rest with one of their ends on the internal load-bearing wall of the building or an internal column. Farms of the latter type are called “slope”.
Correct placement and fastening of these building elements is the basis for ensuring that the upper part does not deform under the influence of possible loads.
How to install rafters correctly
General provisions When designing the roof of a building, determining the number of trusses and the distance between them, be sure to take into account required section timber used for rafters is determined by its material and optimal length rafters. Typically, timber from trees is used to construct rafters., with a cross section of 50x150 mm (considered the most used) or more.
The length of the trusses directly depends on the size of the building box, the type of roof, as well as its height. The cross-section of the timber used and the distance between the rafters determine the strength of the supporting structure for the roof. The distance between the axes of adjacent trusses is called and calculated when designing the roof. In practice, the pitch used can range from 600 to 2000 mm. This step is related to the length of the trusses: the shorter they are, the greater the distance between them they can be installed.
There is a generalized method for calculating the specified distance. It consists in the fact that the preliminary pitch of the rafters is determined from the table. Having then measured the length of the roof overhang of one slope along the lower edge, the resulting distance must be divided by the step determined from the table. The result obtained and the unit added to it after rounding to big side will correspond to the number of rafters required for one slope of the designed roof.
The exact distance between the axes of the “legs” of neighboring trusses will be obtained by dividing the length of one roof slope by the number of rafters calculated for it.
In this way it is possible to determine through what minimum distance rafters can be installed so that the roof supporting structure meets the design load requirements.
However, this method does not take into account possible additional loads on the design associated with the application various kinds roofing coverings, from slate to ondulin. It does not take into account the need to organize free space between the trusses to accommodate the sheets or slabs of insulation used for the roof.
In the case where it is planned to use insulating materials, the width of the canvases or panels of which is known, you can immediately determine at what distance the rafters should be installed. It is recommended in such cases to equate the step to the width of the insulation, minus 1.5 to 2 mm.
Recommendations for choosing rafter spacing for different roofing coverings
For corrugated roofing, the pitch is selected in the range from 600 to 900 mm. In this case, timber is recommended optimal cross section– 50x150 mm.
A heavy roof made of ceramic tiles is characterized by an increased load on the rafters, about 60 - 70 kg/m2. The pitch is recommended in the range from 800 to 1300 mm. Moreover, it can increase in proportion to the increase in the angle of inclination of the roof. For example, the distance between the trusses should be no more than 800 mm if the roof slope does not exceed 15 0. By increasing the specified angle to 70 0, the step can be increased to the maximum. The cross-section of timber for such a roof is recommended from 50x150 to 60x180 mm.
The structure of the supporting structure of the roof covering for metal tiles is not much different from the standard one. The material, compared to ceramics, is almost twice as light: the load per 1 m2 does not exceed 30 kg. It is recommended to use timber with dimensions of 50x150 mm. Some features of fastening the upper ends of the rafters are related to ensuring ventilation of the metal roof to prevent condensation.
Slate roofing is for numerous buildings optimal solution, despite the fact that this material is recognized as harmful and is prohibited for use in European countries.
Recommendations for installing rafters for roofing from wavy slate typical: they are placed in intervals from 600 to 800 mm, they can be 50x100 or 50x150 mm.
For ondulin roofing, it is proposed to follow the recommendations valid for slate roofing. Modern innovative material ondulin looks like slate, but is lighter last time at five.
The determination of the inter-rafter distance for multi-slope (hip) roofs is carried out separately for each slope. For buildings in which the “box” is assembled from logs or timber, the lower end of the rafters is attached directly to the upper part of the external load-bearing wall, and not to a special beam laid along the perimeter of the upper part of the building (mauerlat). This installation method makes it especially high price errors when determining the pitch of the rafters, since it can be very difficult to eliminate such an error.
Load-bearing truss structure for attic roof
For such roofs, the supporting structures for the roof are usually made of wooden beam. The pitch of the rafters for a slope no more than 15 m long can be selected in the range from 800 to 1000 mm. For attics with slopes longer than 15 m, it is recommended to use metal rafter trusses.
It should be noted that for all types of roofs, when determining the pitch of the rafters, the presence of existing vertical structural elements of the building passing through the attic and roof should be taken into account. Such elements include chimneys and air ducts. If the calculated installation point of the truss coincides with the location of the existing pipe or other building elements that cannot be moved to another part of the attic, the rafter placement plan should be changed accordingly.
If changing the specified plan is for some reason impractical, it is recommended that the rafter, which coincides in place with the building element, be arranged so that it is interrupted at the point where the pipe passes. Moreover, the ends of this truss, cut before and after the pipe being passed through, must rest on the corresponding jumpers connecting adjacent rafters.
It must be borne in mind that the nodes of such “interception” of the truss should be made with the necessary reliability and quality, allowing it to correspond to the calculated reliability of the load-bearing structure of the roof covering.
It should be noted that the installation of rafters is part of a whole complex of very serious and very important construction work on the construction of the roof of the building. As a structural element of the load-bearing roofing system of a building, rafters are indicated in the roof design plan, which reflects the results of calculations of various possible loads.
Such calculations must take into account all sorts of factors that influence the designed structure as a whole:
- necessary and sufficient height and slope of the roof;
- optimal material for roofing;
- parameters for its placement on the required sheathing and total weight roofing;
- the necessary load-bearing capacity of the rafter structure in general and the corresponding parameters of the rafters in particular;
- the method of attaching the roof to the walls of the building and the condition of the walls.
And other equally important data, without taking into account which the constructed building and its roof may not withstand various loads.
Therefore, in order not to have distressing consequences as a result of inept actions, it is better to entrust issues related to the design and construction of buildings to professionals who have the necessary experience and knowledge. At least in the part that concerns calculations of the load on rafter structures.
The roof frame must be reliable and durable. But without proper calculations this is difficult to achieve. In the process of carrying out calculations, they determine at what distance to place the rafters on the roof.
What can result from an incorrect or inaccurate calculation of the loads to which the truss structure will be subjected? To the very negative consequences, ranging from deformation of the rafter legs and damage to the roof covering and ending with the collapse of the base of the roof frame. Therefore, when designing buildings, the list of mandatory calculations contains data on what the distance between the roof rafters should be. There is a certain technique that allows you to calculate this value.
Method for calculating the distance between rafters
The distance between the rafters on the roof is called the rafter pitch. As a rule, the pitch of the rafter legs in a roof structure usually exceeds one meter, and the minimum gap ranges between 60 centimeters.
Calculation required quantity rafters for a roof of a certain length and the pitch of the rafters are made as follows:
Rafter structure for metal tiles
When constructing suburban private real estate, metal tile roofing can be found most often. This roofing material is similar to clay tile flooring, but has a number of advantages over it. Sheet metal shingles are easy to install, so you can build a roof in less time. short time, rafter system under metal tiles is also not difficult.
Metal tiles are lighter than ceramic products; the difference in weight sometimes reaches 35 kilograms per square meter, depending on the thickness of the products (read also: ""). Thanks to a significant reduction in the weight of the roof deck, it becomes possible to reduce the thickness of the elements of the rafter structure and the cross-sectional dimensions of the sheathing bars, and to increase the installation pitch of the rafters.
Under the metal tile covering, rafter legs are mounted at a distance of 600 to 950 millimeters, while the cross-section of the construction material is 150 by 50 millimeters. According to experts, in this case, if you place insulation 150 millimeters thick between the rafters, then such thermal insulation will create comfortable conditions for staying in the attic room. At the same time, for greater reliability, it is advisable to choose 200 mm insulation.
When installing rafters, to ensure ventilation of the space filled with insulation, holes with a diameter of 10-12 millimeters are drilled in the rafters near the upper roof.
The technology for creating a rafter system for metal tiles does not differ significantly from designs for other types of roofing materials. The only peculiarity is that the upper support of the rafters is mounted on the ridge girder from above, and not on the side of the ridge beam. The presence of a free zone between the rafters ensures air circulation under the roof deck, and this, due to the use of metal material, reduces the risk of condensation.
Rafter system of a pitched roof, main advantages and characteristics ").
The distance between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. The approximate step between the rafter legs is 1-1.2 meters (read: ""). Rafters regulate the amount of roof overhang.
The reliability of the roof and its service life mainly depend on how correctly the calculations are made.
One of the most important parameters 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, deformation may occur and the roof will collapse.
Therefore, it is extremely important to accurately calculate the spacing when drawing up a roof project.
Basic principles of calculation
The pitch of the rafters is the distance from one rafter leg to the other.
When constructing roofs of private houses, this value is 1 meter.
But this figure is approximate.
To get the exact size of the interval, you need to perform a calculation bearing capacity rafter system of the selected type.
To perform the correct calculation, use the following scheme:
- 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 pitch. If you previously selected its value as 1 meter, then you need to divide by 1.
If you chose 0.8, then you should divide 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 obtain 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 understand this better, let's look at an example.
Having measured 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.
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 = 0.95 m.
This means that in our case, the pitch of the rafter legs should be 0.95 meters.
This is a general calculation.
In which the peculiarities of a particular roofing material are not taken into account.
And he can significantly change this parameter.
When you know what kind of material you will use on the roof, you will have to make some changes to the calculation procedure.
Optimal and minimum value
The step is a unit of calculation.
After all, it depends, first of all, on the load on the roof frame and the cross-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 sheathing may begin to sag.
And how to install the insulation?
After all, most materials have a width of 1 meter.
So when calculating, they take an approximate step of 1 meter.
The minimum distance between is 70 cm.
And to receive optimal value For each material it is necessary to perform calculations.
Determining the pitch for a pitched roof
The pitched roof is the simplest.
After all, in roof truss Such a roof has only rafter legs.
There are no struts, racks, or braces in its design.
Such a roof is usually installed on garages, outbuildings, and bathhouses.
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, 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 it’s easy to explain such popularity: the design is very simple, but despite all its simplicity, the gable roof is distinguished by its reliability.
Its design can be easily adjusted to any climatic conditions and any roofing material.
When calculating the pitch of the rafters of a gable roof, everything is done according to common system calculation (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 are 70 and 120 cm.
What is the pitch depending on the roofing material
Ondulin
If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a cross section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and no more than 90 cm from each other.
A sheathing of timber with a cross-section of 40 x 50 mm is laid on top.
Metal tiles
Metal roofing during construction country houses is used most often.
Because this material is much lighter than ceramic or cement tiles.
Although appearance very similar to her.
A small one makes it possible to use boards of a smaller cross-section when creating a rafter system, and to use thinner bars for sheathing.
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.
When constructing a rafter system under metal tiles, 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 you place insulation with a thickness of 150 mm in the space between the rafters, then attic The most comfortable living conditions will be created.
To ensure ventilation of the space where the insulation is laid, when installing the rafter system, holes near the upper roof with a diameter of 12 mm are drilled.
The technology for manufacturing a rafter 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 girder.
The presence of a free zone between the rafters allows air to fully circulate under the flooring, which helps prevent condensation from forming.
Ceramic tiles
System design under ceramic tiles has its own characteristics.
After all, clay is used to make such roofing material.
And this is very heavy material.
If you compare metal tiles and ceramic tiles, the latter weighs 10 times more.
Accordingly, the rafter system is significantly different.
For 1 square meter of roof surface there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.
Rafters for this frame system made from wood that has undergone long-term drying.
Such wood should have a moisture content of no more than 15%.
A beam with a cross-section of 50 x 150 or 60 x 180 mm is used.
It's more reliable.
And the distance between can be 80 - 130 cm.
The exact value can be given 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 greater - 130 cm.
The interval between rafters is not greater than 130 cm.
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 made.
If the angle of inclination is 45 degrees, then the roofer can safely move on the roof if the rafter pitch is 80 cm.
Corrugated sheet
When creating a rafter system for corrugated sheets, the minimum distance between them is 60 cm.
The maximum size is 90 cm.
If for some reason the pitch of the rafters is more than 90 cm, then it becomes necessary to install cross-section boards of large cross-section.
The rafter legs themselves can have a cross-section of 50 x 100 or 50 x 150 mm.
Slate
Despite the appearance large quantity new roofing materials, asbestos-cement slate remains one of the most popular.
If you plan to lay slate on the roof, then the rafters should have a cross-section of 50 x 100 or 50 x 150 mm.
The distance between them is made no less than 60 and no more than 80 cm.
The lathing is made of timber with a cross-section of 50 x 50 mm or boards with a cross-section of 25 x 100 mm.
When installing any building structure It should be remembered that there are still unforeseen situations.
And, therefore, at and the distance between them it is necessary to provide a safety margin.
Video about installation of the rafter system.
The distance between the rafters is one of the key parameters affecting the strength of the structure. Proper calculation of the installation pitch of the rafters allows you to build a roof that is resistant to high operating loads.
Roof loads and calculation of the rafter system
Development of a project for a single-pitched or gable roof begins with choosing the type of rafter system, the angle of inclination of the slopes (roof height) and materials for constructing the structure. Calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Constant loads include:
- the weight of the materials from which the rafter system is made;
- roofing weight;
- weight of materials roofing pie(waterproofing, vapor barrier, insulation);
- weight of finishing elements residential attic or attic.
In addition to permanent loads, the roof also experiences temporary loads, which include:
The pitch refers to the distance between the rafters of one slope. When calculating a single slope, gable or complex roof, usually follow the following scheme:
- the length of the future roof slope is measured;
- the resulting value is divided by the optimal numerical value of the rafter pitch;
- one is added to the resulting value, the result is rounded;
- the length of the roof slope is divided by the rounded result.
The final result will allow you to determine at what distance the rafter legs should be placed. Determining the step cannot be extremely accurate, since it is necessary to take into account whole line additional factors, including the width of the insulation, installation features of the sheathing under different kinds roofing material. If a roof with a chimney is being designed, the pitch can be adjusted taking into account its location, so that you do not have to subsequently remove part of the rafters and install a supporting structure, such as a special rafter system.
Distance between rafters under slate
Slate is a traditional roofing material. Its advantages include characteristics such as resistance to external influences (excluding mechanical) and low cost. Slate allows you to create a roofing covering, the repair of which can be reduced to replacement individual elements. Slate is heavy and requires the installation of a fairly powerful rafter system. Calculation of the distance at which it is necessary to place the rafters under the slate is carried out taking into account the cross-section of the beam for the manufacture of rafter legs.
The optimal solution is to install a system under slate, in which the gap between the rafters should be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the sheathing is made of timber or boards with a cross-section of at least 30 mm. When calculating the rafter system for slate, you should read that this material has quite large restrictions on the choice of slope angle.
Rafters for metal tiles
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a pitched, gable, hip or complex roof. The frame for metal tiles is built according to standard principles. To calculate at what distance it is better to install the rafters, it is necessary to take into account the loads and the angle of the roof. Metal tiles are characterized by their relatively low weight, thanks to which they can serve as a replacement for old slate or ceramic tile roofing. In this case, the rafters will not need to be strengthened or the pitch of their installation changed.
The standard pitch of rafters for metal tiles is 600-900 mm. The cross-section of the elements can be 50-150 mm - this is enough to create a reliable frame for metal tiles. But if you plan to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, for rafters under metal tiles it is recommended to use 200x50 timber so as not to install additional system holding the insulation. It is better to adjust the gap between the rafters for metal tiles to the width of the sheet or roll insulation.
Corrugated sheeting: rafters and sheathing
Corrugated sheeting is a lightweight and easy-to-use roofing material. Galvanized or coated with a decorative protective layer, corrugated sheets can be used for installing a pitched roof utility room or a garage, or for a gable roof of a residential building. How to calculate the distance required to install rafters under corrugated sheets?
To ensure the necessary structural rigidity, it is enough to install the rafters under the corrugated sheets in increments of 600-900 mm. In this case, you need to pay attention to the angle of the roof. Calculations show that under high external loads, it is better to lay corrugated sheets on the system with a minimum step. But if the distance between the rafters under the corrugated sheet is close to the maximum, and the roof slope angle is small, then the structure is strengthened by using more frequent sheathing. In this case, the pitch of the sheathing under the corrugated sheet should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofs include bitumen and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. Soft roofing is characterized by relatively low weight and the absence of the need to install a massive rafter structure.
The minimum distance between the rafter legs is 600 mm, the maximum is 1500 mm. When installing a support under soft roof it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous sheathing should be. The choice of step is also influenced by the thickness of the material for the sheathing - the thicker the sheet of plywood or OSB, the larger the installation step of the rafter legs can be.
Ondulin: calculation of rafters
Ondulin (bitumen slate) is laid on a flat, continuous sheathing made of sheet material. This allows the roofing covering to successfully resist wind and snow loads. The sheathing for ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or pitched roof.
Rafters for ondulin are made of timber with a section of 200×50 mm. When choosing at what distance to place the rafter legs for the structure under the ondulin, it is recommended to take into account the width insulation material to make it easier to install. This calculation allows us to reduce financial expenses for the installation of the roof.
Sandwich panel roof
Sandwich roofing is most often erected on houses made of sip panels or hangar-type buildings. A special feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the top of the wall (or the distance between supporting structures pitched roof) allow the installation of a sandwich without additional supports.
If the span exceeds 4 meters, additional purlins must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case, the rafters can be positioned at larger intervals - they serve as a support for the purlins. The distance between the rafter legs is selected based on the length of the available material for the purlins and the length load-bearing walls. Technical specifications sandwich allow the roof to withstand high operating loads.
Polycarbonate: construction of a supporting structure
Polycarbonate in Lately is actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, canopies, winter gardens. The lathing and rafter system for polycarbonate can be made of wood or metal.
Polycarbonate varies in weight depending on the thickness of the sheet. It is recommended to perform lathing under polycarbonate in increments of 600-800 mm. The sheathing (wooden or metal) is mounted on the rafters, which can be straight or have arched shape. Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to lower the rafters, it is necessary to take into account the glazing area, the size and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.
The distance between the rafters of a gable and pitched roof
Find out what distance between the rafters needs to be made for a gable and shed roof. The maximum distance between rafters for metal tiles, ondulin and soft roofing.
What is the distance between the rafters of a gable roof?
Erection of the roof - The final stage any construction. This structural element is load-bearing structure, which takes on all the loads and then evenly distributes them over the surface of the load-bearing walls of the house.
Gable roof
A gable roof is rightfully considered the most common option for arranging suburban housing. And there is a completely logical explanation for this. It's no secret that what simpler design, the easier it is to build and the higher its reliability and performance characteristics.
Gable roof has a triangular shape and consists of two pitched planes connected at the highest point by a ridge girder, and the same number and shape of pediments.
In principle, the construction of a gable roof is not considered so complex operation. But, despite all its simplicity, it requires the most responsible and thoughtful approach.
Structurally, a gable roof has two slopes located in relation to the wall elements of the house at a certain angle, ensuring natural removal of precipitation from its surface. Also gable roofing structures may be attic or mansard type.
As a rule, gable roofs are installed on single-story, simple architectural plan structures. A huge advantage is that the rafters in this case will not be particularly difficult to install.
The angle of inclination of the roof slopes of gable roofs
The angle of inclination of a gable roof cannot be less than 5 degrees, and in some cases it can even reach 90 degrees. Only at this angle of inclination of the roof slopes will the rafters be able to adequately cope with the function assigned to them.
To choose the angle of inclination of the slopes for gable roof influences great amount factors such as climatic conditions, the type of roofing material chosen and architectural style building.
For example, flat roofs are ideal for construction in areas where strong hurricane winds constantly blow, but structures with steep slopes are an excellent option for those areas where significant amounts of precipitation fall.
Also, the angle of the roof affects its cost, this is due to the fact that a roof with a small angle of roof slopes will use much more roofing material than one with a large one.
However, this is not the only important parameter when building a gable roof. No less important when forming a gable roof is correct installation and fastening of the rafter system, as well as the step size between its elements.
The quality of the structure is also affected by the attachment of the rafters to the mauerlat and the ridge girder. Especially reliable fastening can be formed using cutting and additional fixation of connections with bolts.
The distance between the rafter legs (otherwise known as the pitch of the rafters) is considered one of the most important parameters when installing a roof, which affects its strength characteristics.
A correctly calculated pitch between the rafters of a gable roof allows you to create a roof that is resistant to the high loads to which it will be subjected during operation.
Let's take a closer look at what the distance between the rafter legs should be.
Rafter spacing for a gable roof
The distance between the rafters of a gable roof is calculated during design. Correcting any mistakes made at this stage is quite problematic, and therefore if you are not sure own strength, then it is better to entrust its implementation to professional architects.
Reliable rafters are the basis of any house roof.
The rafter pitch is calculated taking into account the loads to which the structure will be subjected during operation and the angle of inclination of the roof slopes.
When making a competent calculation, the presence or absence of an insulating layer, the cross-section of the structural elements of the rafter system, the type of sheathing and roofing must be taken into account. It is necessary to correctly calculate the loads, as this will help you avoid making mistakes when choosing the rafter section.
The rafter pitch is the distance between two adjacent trusses.
Step-by-step instructions for calculating rafter pitch for a gable roof:
- We calculate the estimated length of the roof slopes.
- Divide the resulting number by optimal sizes step.
- Add one to the resulting number and round the result.
- We divide the length of the slopes by the rounded result.
As a result of these simple calculations, you will get the distance at which the rafters should be installed.
The pitch between the rafters cannot be calculated accurately, since to obtain more accurate data it is necessary to take into account a huge number of parameters, ranging from the width of the insulating layer, the type of roofing material and even the distance between the gable roof sheathing elements. Rafters installed correctly will serve you faithfully for decades.
Rafter spacing under asbestos-cement slate
An important parameter of asbestos-cement slate is its significant weight, due to which it requires the installation of powerful rafters that can withstand heavy loads. The distance between the rafters is selected based on the cross-section of the timber used to make the rafters.
It is equally important that the rafters of a gable roof are fastened correctly, as this will provide it with a high degree of reliability and a long service life.
The optimal pitch between the rafters when using asbestos-cement slate should not be less than 800 mm. Thanks to this, the rafters will be able to easily cope with the task assigned to them.
Rafters for metal tiles
We will not talk about all the advantages and disadvantages of this material; a lot has already been said about this. Let's take a better look at what the step should be between load-bearing elements designs. Rafters for metal tiles are installed in accordance with existing standards and requirements.
Due to its low weight, this coating can be used to cover roofs that previously had ceramic tiles or asbestos-cement slate laid on them.
The size between the rafters in this case ranges from 600 to 900 mm, and the cross-section of the lumber is 50 by 150 mm. This step between the rafters will create the most reliable load-bearing frame for the roof.
However, in areas characterized by snowy winters, it is preferable to arrange a distance between rafters of 200 mm, and to use timber with a section of 50 by 200 mm for the manufacture of structural elements.
In order not to install a special system to maintain the insulation, you can adjust the distance between the rafters to the width of the thermal insulation material.
Rafters for ondulin
Ondulin or flexible tiles must be laid on a continuous, perfectly flat sheathing, and it is better if it is made of some kind of sheet material, which will allow the roof to withstand all loads.
The sheathing is attached to the rafter legs, located in increments of 600 to 1000 mm, depending on the angle of inclination of the roof slopes of the gable roof.
The correctly selected distance between the elements of the rafter system guarantees everything supporting frame high degree of strength and durability of the entire structure.
What is the distance between the rafters of a gable roof, YouSpec Construction Encyclopedia
The correctly selected distance between the elements of the rafter system guarantees the entire supporting frame a high degree of strength and durability of the entire
Distance between rafters: correct calculation
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, deformation may occur and the roof will collapse.
Therefore, it is extremely important to accurately calculate the interval between the rafters when drawing up a roof project.
Basic principles of calculation
The pitch of the rafters is the distance from one rafter leg to the other.
When constructing roofs of private houses, this value is 1 meter.
But this figure is approximate.
To obtain the exact size of the interval, it is necessary to calculate the load-bearing capacity of the rafter system of the selected type.
To perform the correct calculation, use the following scheme:
- 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 pitch. If you previously selected its value as 1 meter, then you need to divide by 1.
If you chose 0.8, then you should divide 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 obtain 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 understand this better, let's look at an example.
Having measured 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.
Now we add the unit 27.5 m +1 = 28.5 m.
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 = 0.95 m.
This means that in our case, the pitch of the rafter legs should be 0.95 meters.
This is a general calculation.
In which the peculiarities of a particular roofing material are not taken into account.
And he can significantly change this parameter.
When you know what kind of material you will use on the roof, you will have to make some changes to the calculation procedure.
Optimal and minimum value
The step is a unit of calculation.
After all, it depends, first of all, on the load on the roof frame and the cross-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 sheathing may begin to sag.
And how to install the insulation?
After all, most materials have a width of 1 meter.
So when calculating, they take an approximate step of 1 meter.
The minimum distance between rafter legs 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
The pitched roof is the simplest.
After all, in the truss of such a roof there are only rafter legs.
There are no struts, racks, or braces in its design.
Such a roof is usually installed on garages, outbuildings, and bathhouses.
As can be seen from the table, the rafter pitch 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 it’s easy to explain such popularity: the design is very simple, but despite all its simplicity, the gable roof is distinguished by its reliability.
Its design can be easily adjusted 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 maximum pitch values for the rafter legs are 70 and 120 cm.
What is the pitch depending on the roofing material
If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a cross-section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and no more than 90 cm from each other.
A sheathing of timber with a cross-section of 40 x 50 mm is laid on top.
Metal tiles
Metal roofing is most often used in the construction of country houses.
Because this material is much lighter than ceramic or cement tiles.
Although in appearance he is very similar to her.
The low weight of metal tiles makes it possible to use boards of a smaller cross-section when creating a rafter system, and to use thinner bars for sheathing.
More about the counter-lattice for metal tiles.
ABOUT hip roof With hanging rafters link. Also about the design of hanging rafters.
About the price of Viking metal tiles here. Specifications, photos, reviews.
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.
When constructing a rafter system under metal tiles, 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 insulation with a thickness of 150 mm is placed in the gap 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 near the upper roof with a diameter of 12 mm are drilled.
The technology for manufacturing a rafter 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 girder.
The presence of a free zone between the rafters allows air to fully circulate under the flooring, which helps prevent condensation from forming.
Ceramic tiles
The design of the system for ceramic tiles has its own characteristics.
After all, clay is used to make such roofing material.
And this is very heavy material.
If you compare metal tiles and ceramic tiles, the latter weighs 10 times more.
Accordingly, the rafter system is significantly different.
For 1 square meter of 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 of wood that has undergone long-term drying.
Such wood should have a moisture content of no more than 15%.
A beam with a cross-section of 50 x 150 or 60 x 180 mm is used.
And the distance between the rafter legs can be 80 - 130 cm.
The exact value can be given 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 may be larger - 130 cm.
The interval between rafters is not greater than 130 cm.
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 made.
If the angle of inclination is 45 degrees, then the roofer can safely move on the roof if the rafter pitch is 80 cm.
Corrugated sheet
When creating a rafter system under corrugated sheeting, the minimum distance between the rafter legs is 60 cm.
The maximum size is 90 cm.
If for some reason the pitch of the rafters is more than 90 cm, then it becomes necessary to install cross-section boards of large cross-section.
The rafter legs themselves can have a cross-section of 50 x 100 or 50 x 150 mm.
Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.
If you plan to lay slate on the roof, then the rafters should have a cross-section of 50 x 100 or 50 x 150 mm.
The distance between them is made no less than 60 and no more than 80 cm.
The lathing is made of timber with a cross-section of 50 x 50 mm or boards with a cross-section of 25 x 100 mm.
When constructing any building structure, it should be remembered that there are still unforeseen situations.
And, therefore, when calculating the sections of rafters and the distance between them, it is necessary to provide a safety margin.
Distance between rafters: single-pitched, gable roof
One of the most important parameters when calculating a rafter system is the distance between the rafters. After all, it depends on it how strong and stable it will be.