The distance between the rafters is one of key parameters, affecting the strength of the structure. Proper calculation of the installation pitch of the rafters allows you to build a roof that is resistant to high operating loads.
Roof loads and calculation of the rafter system
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;
- weight roofing;
- weight of roofing materials (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, the installation features of the sheathing under different kinds roofing material. If a roof with a chimney is being designed, the pitch can be adjusted taking into account its location, so that you do not have to subsequently remove part of the rafters and install a supporting structure, such as a special rafter system.
Distance between rafters under slate
Slate is a traditional roofing material. Its advantages include characteristics such as resistance to external influences (excluding mechanical) and low cost. Slate allows you to create a roofing covering, the repair of which can be reduced to replacing individual elements. Slate has heavy weight and requires the installation of a sufficiently powerful rafter system. Calculation of the distance at which it is necessary to place the rafters under the slate is carried out taking into account the cross-section of the beam for the manufacture of rafter legs.
The optimal solution is to install a system under slate, in which the gap between the rafters should be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the sheathing is made of timber or boards with a cross-section of at least 30 mm. When calculating a rafter system for slate, you should read that this material has quite large restrictions on the choice of the angle of inclination of the slopes.
Rafters for metal tiles
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a pitched, gable, hip or complex roof. The frame for metal tiles is built according to standard principles. To calculate at what distance it is better to install the rafters, it is necessary to take into account the loads and the angle of the roof. Metal tiles are characterized by their relatively low weight, thanks to which they can serve as a replacement for old slate or ceramic tile roofing. In this case, the rafters will not need to be strengthened or the pitch of their installation changed.
The standard pitch of rafters for metal tiles is 600-900 mm. The cross-section of the elements can be 50-150 mm - this is enough to create a reliable frame for metal tiles. But if you plan to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, for rafters under metal tiles it is recommended to use 200x50 timber so as not to install additional system holding the insulation. It is better to adjust the gap between the rafters for metal tiles to the width of the sheet or roll insulation.
Corrugated sheeting: rafters and sheathing
Corrugated sheeting is a lightweight and easy-to-use roofing material. Galvanized or coated with a decorative protective layer, corrugated sheets can be used for installation pitched roof a utility room or garage, as well as for a gable roof of a residential building. How to calculate the distance required to install rafters under corrugated sheeting?
To ensure the necessary structural rigidity, it is enough to install the rafters under the corrugated sheets in increments of 600-900 mm. In this case, you need to pay attention to the angle of the roof. Calculations show that under high external loads, it is better to lay corrugated sheets on the system with a minimum step. But if the distance between the rafters under the corrugated sheet is close to the maximum, and the roof slope angle is small, then the structure is strengthened by using more frequent sheathing. In this case, the pitch of the sheathing under the corrugated sheet should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofs include bitumen and bitumen-polymer rolled materials, roofing membranes, and 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 from sheet material. This allows the roofing covering to successfully resist wind and snow loads. The sheathing for ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or pitched roof.
Rafters for ondulin are made of timber with a section of 200×50 mm. When choosing at what distance to place the rafter legs for the structure under the ondulin, it is recommended to take into account the width insulation material to make it easier to install. This calculation allows you to reduce the financial costs of roofing.
Sandwich panel roof
Sandwich roofing is most often erected on houses made of sip panels or hangar-type buildings. A special feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the top of the wall (or the distance between 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 big step– 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 of the 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 lathing (wooden or metal) is mounted on rafters, which can be straight or arched. Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to lower the rafters, it is necessary to take into account the glazing area, the size and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.
The distance between the rafters of a gable and pitched roof
Find out what distance between the rafters needs to be made for a gable and shed roof. Maximum distance between the rafters under 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
Gable roof is rightfully considered the most common option for arranging suburban housing. And this exists completely logical explanation. It's no secret that what simpler design, the easier it is to build and the higher its reliability and performance characteristics.
The 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 gables.
In principle, the construction of a gable roof is not considered such a 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 can be attic or mansard type.
As a rule, gable roofs are installed on one-story, architecturally simple 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 influenced by a huge number of 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 proper calculation, the presence or absence of an insulating layer and the cross-section must be taken into account. structural elements rafter system, type of sheathing and roofing. 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.
Thanks to low weight this coating can be used to cover roofs that have previously been covered with ceramic tiles or asbestos-cement slate.
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 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 another.
When constructing roofs of private houses, this value is 1 meter.
But this figure is approximate.
To obtain Exact size interval, it is necessary to calculate the load-bearing capacity of the rafter system of the selected type.
For execution correct calculation the following scheme should be used:
- first you need to determine the length of the roof slope;
- Now the resulting figure should be divided by the value of the approximately selected rafter 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 receive exact amount 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 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 limit values pitch of rafter legs 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 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.
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 at the 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 space between the rafters, then the most efficient conditions will be created in the attic space. comfortable conditions for accommodation.
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.
Mounting of the upper support is not carried out ridge beam on the side, and on the ridge run.
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.
On 1 square meter the roof surface bears 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 for corrugated sheets 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 installing 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.
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 decking made from clay tiles, but compared to it has a number of advantages. Sheet metal tiles are easy to install, so you can build a roof in a shorter time; the rafter system for metal tiles is also not complicated.
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 150 millimeters thick insulation 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.
One of important stages Any construction is the construction of the roof of the building, the basis of which is the installation of the rafter system. The uniform distribution of the weight of the roof on the frame, the reliability of the roof and the duration of its operation as a whole will completely depend on how correctly the pitch of the rafters is chosen, i.e. the distance between them. Any minor calculation error can cause damage and collapse of the entire roof.
Collection of the required calculated values to establish the pitch of the rafters
Rafter system includes the following components:
- farms;
- ridge and side girders;
- Mauerlat;
- diagonal elements.
Trusses consist of a crossbar, a base, rafter legs, connecting and fastening elements. Rafter legs are beams located along the slopes, the lower ends of which are connected to the Mauerlat, and the upper ends to the purlins.
The content of the articleThe rafter pitch is the exact distance between two rafter legs.
To obtain the exact indicated value, you must first know the values of some important quantities.
It is correct to make all calculations for the roof covering system at the design stage of the house. You can carry out such a responsible task yourself or entrust it to specialists. The more accurate the calculations are, the stronger the foundation for the roof will be.
To correctly make all the required calculations, including the pitch of the rafters, you need to know:
- permanent and temporary loads;
- their size;
- slope angle;
- type of roofing;
- rafter material;
- roof type.
One of the indicators that must be taken into account when calculating the rafter pitch is permanent and temporary loads. These include:
- weight of the roofing and rafter structure;
- weight interior decoration roofs;
- weight of snow cover;
- the weight of the person performing the roof maintenance.
It should be noted that these data are taken in special tables developed by scientists, depending on climatic zones, across various territorial regions.
The slope angle can be determined by knowing the length of the house wall and the height of the roof. The steeper the roof, the more is installed, since the load on such roofs will be transferred mainly to the load-bearing walls. After making further calculations, the length of the rafters can be easily calculated. Most often they have standard sizes: 4 and 6 m.
Wood is a good choice for making a roofing system. coniferous species trees. The lumber must be of high quality, without knots or rot. Everything before work wooden elements need to be treated with antiseptic special compounds.
The pitch of the rafters will also depend on the type of roof, i.e. functional features and its forms. The size of a simple and complex roof will be different.
How the type of roofing will influence the pitch of the rafters should be considered in more detail.
General technology for calculating the distance between rafters
Having made all the necessary measurements, you can make a constructive calculation of the rafter pitch. Based on practice, this indicator ranges from 0.6 to 1.0 m.
To correctly perform this calculation yourself, you must adhere to the following technology:
- The total length of the roof slope is taken.
- The optimal pitch of the truss is selected.
- The length of the slope must be divided by the pitch of the rafters.
- One is added to the resulting value.
- To obtain a whole number, the result is rounded up.
- This calculation finds the quantity roof trusses(rafter legs) located on one roof slope.
- Now the entire length of the roof slope is divided by the resulting value, which shows the number of trusses. This determines the pitch of the rafters.
It should be noted that this calculation is made at the center of the future rafters. However, the calculations cannot be considered accurate and constant. In each case of building a house roof, the angle of the roof slope, the features of the selected roofing material, and other indicators are taken into account. In this regard, it is necessary to consider the features of choosing rafter pitches for the most common roofing materials: metal and ceramic tiles, corrugated sheets, slate and ondulin.
Features when choosing the distance between the rafters for metal and ceramic tiles
Metal tiles as a roofing covering are extremely common in both urban and suburban construction. The design of the roof truss system itself when using metal tiles will differ little from general scheme. However, due to the fact that this building material is light in weight, rafters and other elements of the system can be taken with a smaller cross-section, i.e., with a smaller margin of safety. The distance between the rafters when using metal tiles is 60-95 cm. Performing all roof installation work using metal tiles is much easier than using other roofing materials. A special feature of the lathing design of this material is that the board near the eaves should be about 1.5 cm thicker than the rest. Typically, the cross-section of metal tile rafters is 50x150 mm.
Ceramic tiles are roofing materials that have a significant weight, which is 10 times the weight of metal tiles. In this regard, it is necessary to take a more thorough approach to calculating the roof truss system. should be increased slightly - up to 60x180 mm. The average distance between the rafters for covering with ceramic tiles is set in the range of 0.8-1.3 m. The slope angle of the slopes must be taken into account: the distance between the rafters is greater, the higher the roof.
The length of the rafter legs in this case will have a strong influence on the result. The distance between the rafters decreases as their length increases. With their large length, increased deflection loads may occur, which can be significantly reduced if an additional system of struts, supporting posts and other elements are installed.
Features when choosing rafter spacing for slate, corrugated board and ondulin
The most common roofing material is slate. This is due to its low cost, ease of installation, and the possibility of replacement if individual roof elements are damaged.
The peculiarity of slate lathing is its thinned type, consisting of any type of board or timber, but with a mandatory cross-section of at least 30 mm. This is necessary for proper and high-quality distribution of the weight of the slate on the sheathing.
The optimal distance between the rafters when combining the load from the weight of the slate sheets should be 80 cm. It is worth constantly taking care of the safety margin of the rafter system, which may be due to various unforeseen circumstances. Otherwise, its installation under a slate roof is no different from other options.
Now you should pay attention to some features when installing a rafter system for roofing materials such as corrugated sheets and ondulin.
The weight of corrugated sheeting and ondulin is much lighter than that of ceramic tiles or slate, so the technology for installing rafters for these materials is practically no different from installing metal tiles. The distance between the rafters for a roof made of corrugated sheets is 60-90 cm, and for those made of ondulin - 60-100 cm.
If it is necessary to increase the distance between the rafter legs, it is necessary to strengthen the system structure with transverse elements of the sheathing.
The lathing design for corrugated sheets is very similar to the lathing design for metal tiles. It is important to remember that in this case last board should have a slightly greater thickness than all the others.
A feature of the installation of lathing for ondulin should be considered the need for its continuous type for high-quality resistance to various loads. In some cases, you can use a thinned type of sheathing, but then the pitch between the rafters should be no more than 30 cm.
Thus, being able to produce everything necessary measurements, knowing the basics of installing a rafter system for the main roofing materials (tiles, corrugated sheets, slate and ondulin), you can correctly calculate the distance between the rafters.
When building a roof, the first thing to choose is the type of rafter system. This means that the rafters must be hanging or layered, or the entire rafter system will consist of both rafters, i.e., combined. It is not difficult to calculate the distance between the rafters, knowing the magnitude of the loads that will act on the entire roof.
Loads can be temporary or permanent. Constant loads include:
- the weight of the materials of the rafter system itself;
- weight of roofing material;
- the weight of the elements of the roofing pie, if the roof is insulated;
- weight of the interior finishing of the attic ceiling.
Temporary loads include: weight of snow cover, weight of a person during production roofing works and roof maintenance during operation, wind load and the weight of possible water flows in the summer.
What are the calculations based on?
The distance between the roof rafters is also calculated based on the selected material and the cross-section of the rafters. All calculations are carried out at the house design stage by specialists from design organizations. To do this, they use reference documents and building codes and rules regulating this or that rafter pitch, sheathing pitch and other calculated values.
When building a private house, rarely does anyone order a project where, based on calculations, it is recommended what distance between the rafters should be maintained. Most often, developers rely on the experience of the craftsmen and trust them to carry out all the calculations on site. However, there are those who want to calculate the rafter system themselves and build the roof themselves.
In this case, they must first decide on the type of roof, choose what kind of attic it will be - heated residential or cold, since the type of rafter system and the calculation of the distance between the rafters directly depend on these parameters
Distance between rafters of a pitched roof
The calculation for a pitched roof is the simplest. The rafter system does not provide racks and braces - only the rafters themselves. This type of roof is most often installed on utility rooms, garages, bathhouses, etc.
The pitch of the rafters of a pitched roof is presented in the table below and depends on the cross-section of the timber:
If the developer wants to independently calculate the loads on the rafter system, it will be useful for him to familiarize himself with documents such as SNiP 2.01.85 “Loads and impacts” and “Changes from SNiP 2.01.85”, which contains maps of the climatic regions of Russia.
The material chosen for the construction of the rafter system is coniferous wood, the humidity of which is 20-22%. Boards, beams and other types of lumber must be smooth without curling, rot, knots or blue stains.
All wooden elements should be treated with antiseptics and fire retardants to protect the wood from rotting and fire. The material used, the length of the rafters and the cross-section of the timber also affects the calculations (see table):
Approximate calculation
The pitch of the rafters is nothing more than the distance between the rafter legs. As a rule, for residential private houses this figure is 0.6-1.0 m.
The pitch of the rafters is influenced by a significant number of factors. Calculation required quantity rafter legs are produced in the following way:
- The length of the roof slope is measured. After this, the resulting value is divided by the selected pitch between the rafters.
- Then one is added to the resulting value and rounded up to get a whole number. This is how the number of rafters required for a given length of one roof slope is obtained.
- After this, the entire length of the roof slope is divided by the resulting integer (the number of rafter legs) and as a result, the distance between the axes of the future rafters is obtained, which is called the rafter pitch.
- The axis should run through the center of the rafter. However for different types roof covering, the pitch of the rafters can vary, and it also changes depending on the slope of the roof slope.
For example: the length of the roof slope is 16 meters, and the pitch between the rafters is 0.6 meters. Therefore, 16/0.6 + 1 = 27.66 = 28 meters (rafters are necessary for the installation of the slope)
The greater the slope angle, i.e., the steeper the roof, the larger the pitch of the rafters can be made. This is explained by the fact that the load on steep roofs is not distributed over the entire roof plane, but is mostly transferred to the load-bearing walls.
Rafters for ceramic tiles
Ceramic tiles are a material that has a decent weight. Therefore, to install a tile roof, you should calculate the cross-section and length of the rafters, taking into account that one square meter of ceramics weighs almost ten times more than the weight of metal tiles.
- If the design of the rafter system involves tightening the rafters, then its cross-section should be increased.
- The rafters themselves should be made of dry, healthy wood, their cross-section should be 50x150 or 60x180 mm.
- The pitch of the rafters is made in the range of 0.8 -1.3 m for ceramic tile coverings, and its exact determination depends on the slope angle of the slopes.
The higher the roof, the wider the rafter spacing can be. For example, with a slope angle of 15 degrees, the step will be 80 cm, and if the slope angle increases to 75 degrees, the distance between the rafter legs will increase to 1.3 m.
Another circumstance affects the pitch of the rafters - the length of the rafter legs. The longer they are, the shorter their step. This is explained by the fact that when maximum length rafters create increased deflection loads. They can be reduced by installing a system of supporting posts, struts and other elements of the rafter system, which take on part of the loads from the rafters.
Metal roof rafters
The rafter system for metal tiles is not much different from other rafter structures. But due to the fact that it weighs several times less than ceramic tiles, rafters and all other elements of the roof structure can be made with a smaller margin of safety, i.e., a smaller cross-section. The difference in weight of clay and metal tiles is about 35 kg per 1 m2.
The rafter spacing for metal tiles is usually 0.6-0.9 m. Metal tiles are widely used to cover country houses, which often include attic rooms, so the roof is made insulated. The pitch of the rafters in such structures is adjusted to the size of the insulation, which is inserted between the rafter legs.
The gable roof design for private houses is most often chosen, since it is the best option in terms of ease of installation and ease of use, strength and reliability, as well as style solutions. A gable roof is also called a gable roof and has two slopes, which can be located in relation to each other under the same or different angles, that is, it can be an isosceles or scalene triangle. The latter option can increasingly be found among new buildings, as it becomes fashionable style decision. And, in addition to originality, such a roof has some positive features that simplify its operation.
This type of rafter system can be used for all types of roofing materials, but the sheathing attached to the rafters has its own parameters for each covering.
Gable roof: the rafter system under which has its own characteristics must be carefully studied and calculated in advance, before purchasing materials and installing it. Let's try to understand these issues.
Types of gable roof designs
First you need to figure out what designs gable roofs happen, since you have to choose the most suitable one for a particular building.
- Simple equilateral gable design
This option gable construction can be called traditional and the most used, since it is easy to install and maintain, and is also durable and reliable.
Symmetry in this system helps to achieve uniform load on the mauerlat and load-bearing walls. At making the right choice sections of timber for arranging the rafter system and Mauerlat, these parts will provide the necessary for long-term operation roof safety margin. Additional reliability of the structure will be provided by correctly installed racks, struts and tightening.
The disadvantage of this system for arranging inside the attic space is that after installing the walls and ceiling large area occupy blind areas in corner areas structures that remain unused.
- Simple asymmetrical gable design
The asymmetrical gable design differs from traditional system the fact that its slopes are located at different angles. So, one of them is usually more than 45 degrees, which allows you to increase the usable area of the attic space, in which it is quite possible to equip a living space, of course, with proper insulation.
Another important advantage of such a design may be a smaller slope, which is recommended to be planned on the leeward side of the building, where it is always collected on the roof a large number of snow. A slope that is small in size but has a great steepness will not retain large snowdrifts on its surface.
The disadvantage of an asymmetrical structure is its more complex calculation to achieve uniform distribution of the load on the walls of the house.
- Broken gable structure
This gable rafter system can be called a rarity, although thanks to this arrangement of the slopes in the attic space, quite a large room, which can be used for residential or commercial premises.
In addition to such a rafter system, a broken gable structure can also include attic option installation of rafters.
Both slopes are “broken” - a clear win in usable area attic space
3 – Stand mounted on a bench.
4 – Rafters.
5 – Lathing.
The layered system differs from the hanging system in that it is installed on a building that has internal capital partitions. Capital interior walls are used to secure the beam on them, on which the racks are installed, supporting the ridge girder, to which the upper ends of the rafter legs are fastened. Then the sheathing boards are fixed to the rafters.
This design is more popular than the hanging one, as it is reliable and easy to install.
fastenings for rafters
Hanging rafter system
The diagram of a hanging rafter system looks as shown in the illustration and includes the following main elements:
1 – Load-bearing walls.
2 – Mauerlat.
3 – Rafters.
4 – Lathing.
5 – Tightening (crossbar).
The hanging rafter system is mounted on two external load-bearing walls, onto which the Mauerlat is pre-fixed. This roof option can only be used if the distance between load-bearing walls is no more than 7000 mm, since apart from them there is no additional support for the roof truss structure. Such a system is usually equipped with ties reinforced by slopes - these elements will remove part of the load from the walls of the building.
In addition to layered and hanging systems, there are combined options, which include individual elements of one and the other design.
When the rafter system is selected, it is recommended that before purchasing materials, make detailed drawing roofs with dimensions indicated - this will make it easier to calculate the quantity of everything needed and the amount for their purchase. In addition, such a diagram will significantly help with installation work. But in order to draw up a drawing, you will have to carry out some
How to calculate the parameters of a gable rafter system
Correctly calculate the parameters of the elements for installation work- very important. To do this, it is first recommended to make a list of everything you need and make the calculation step by step. All calculations should be made with a margin of 10–15%, avoiding excessive savings, which would be to the detriment of the quality and strength of the structure.
If you decide to do this part of the work yourself, you must definitely check the technical documents developed by specialists, for example, those posted in SNiP.
The main directions of calculation will be three interrelated quantities - the steepness of the slope, the height of the ridge above the ceiling and the length of the rafter legs. Next, having linear parameters, it will be necessary to determine the cross-section of the material for the rafters. But it, in turn, depends on the loads placed on the rafter system.
Loads on the rafter system
Loads on the rafter system are divided into three categories:
- Constant loads. This category includes those that will constantly keep the rafter system in tension - insulation, if provided, roofing, windproof, hydro- and vapor barrier film, fasteners, finishing materials for the inside of the attic. The weight of all elements and materials required for the roofing “pie” is summed up, and on average the optimal value should be 40-45 kg/m². It is advisable to calculate the materials in such a way that the weight of 1 m² does not exceed 50 kg/m², especially if a roof system with hanging rafters is used.
- Short-term loads. Such loads occur periodically and may have different impact on the design. These include the following impacts:
— weight of people at repair work;
— climatic temperature effects;
— possible loads from ice.
These external loads are highly dependent on the characteristics of the region of construction. In addition, their size directly depends on the steepness of the slopes. For example, on gentle slopes the snow load will play a decisive role. As the roof's steepness increases, the influence of snow pressure decreases, but the dependence on wind influence increases. On slopes steeper than 60 degrees, the snow load is completely written off, but the windage of the roof increases significantly, and the wind becomes the dominant external influence.
Data for calculations can be found in SNiP 2.01.07-85* “Loads and impacts” in the sections “ Snow loads" and "Wind loads". In this case, it is necessary to take into account not only the region where the house is located, but also the place of its construction - lowland or hill, a separate building or surrounded by other buildings.
A convenient algorithm for calculating loads will be given below.
- Special loads. This category includes factors such as seismic impacts, hurricane winds, deformation processes due to soil subsidence, which are usually called force majeure. It is impossible to provide for everything, and in order for the roof to withstand all these tests, it is recommended to provide an additional margin of safety when purchasing materials and installing the structure.
If the roof will be installed on an old building, it is necessary to calculate bearing capacity foundation and walls, since new roof may weigh more than the old one. Such calculations can only be carried out professionally by specialists, but such calculations must be made without fail, otherwise you will have to not only replace the roof, but also repair the entire structure. In this case, specialists will need to provide a roof project, which will indicate all its parameters.
The angle of inclination of the slopes of the rafter system and the height of the ridge
The angle of the roof slopes is determined by the choice, since each of them requires a personal calculation. Often the manufacturer of a particular brand of coating gives necessary recommendations, but if we talk about general requirements, for example, in our case - metal tiles, then the slope angle should be at least 20 degrees.
Increasing the slope angle will significantly expand the attic space, but building such a roof will require more building materials and, of course, the cost of construction will increase significantly.
So, any gable rafter system, no matter whether it is symmetrical or not, can be represented as a triangle.
Its peaks:
- dot "A"- this is the external intersection point. Angle “A” is adjacent to this vertex, which determines the steepness of the roof slope.
- dot « b"- the top of the ridge.
- dot "With"- the intersection of a plumb line from a ridge with a ceiling or simply the upper level of a wall.
Known initial value – « D" length of the base of the triangle. For a symmetrical roof this is half the span. For asymmetrical options, it may be different, this is not difficult to determine.
"N"- height of the ridge above the base (floor);
« L"– the length of the rafter leg, which, if desired, can be increased by "m" to form a cornice overhang.
According to known trigonometric relations:
N =D×tgA
Thus, it is possible either to determine the height of the ridge from a given value of angle A, or, conversely, by planning in advance a certain height of the attic space, to determine the steepness of the slope.
All this can be easily done with the calculator below. Changing the value of the angle " A" you can come to optimal value height " N".
