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 single or double slope project pitched roof starts with choosing a type rafter system, slope angle (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 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 you should place rafter legs. 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 utility room or garage, and for gable roof 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 roll 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 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.
A rafter is one of the individual elements of the supporting structure of the roof, with the help of which its slope is formed. In the design, the rafter is attached with its upper end to the ridge, and with its lower end it rests on the mauerlat, with a straight slope, or on the rack (with a sloping roof). Rafters are made from edged boards section 150x60 mm or timber 150x100 mm. The distance between the rafters at which they are located from each other after installation is called the pitch, which can be in the range of 600 - 1200 mm.
Rafter systems, their types
Depending on the type of installation of rafter legs, systems are divided into 3 types:
What may determine the installation step of the rafters?
The pitch of the rafters on the roof depends on such factors, How:
Taking into account all these indicators when calculating, you can get a strong and reliable rafter structure, which will serve as a high-quality support for the roof for a long time.
It is the calculation, subject to the basics of standard loads, allows you to correctly select the distance between the rafters. As a rule, standard values can be determined from Sheaves, and calculated values are derived on their basis separately for each structure.
In this case, it is accepted as a standard value to use rafter legs with a cross-section of 150x50 mm with an optimal distance between the rafters in the range of 0.8 - 1.8 m/p. but it should be remembered that when the slope of the roof slope changes, the distance between the rafters also changes.
Calculation of truss structure
The strength and stability of the entire roof directly depends on the quality of the calculation for selecting the cross-section of the rafter legs and the distance between them. Regardless of what type of coating is chosen: profiled sheet, slate or metal tile, the initial calculation should remain the same. After all, each calculation is based on structural strength under mechanical loads, and other influences are no longer important.
When calculating the choice of the optimal distance between the rafters for the roof, The following parameters are taken as a basis:
- Type of roof covering.
- Type of rafter system and design features roofs.
- Expediency and savings.
For a small house, you can do the design calculations for the roof yourself. True, the method of calculating elements for a roof truss system is quite complicated, and it is recommended to do it using programs specially created for this. Especially if you need to calculate a complex sloping roof with a large area, most likely, you will not be able to do it without a specialist. In this case, the calculation of the pitch of the rafters will also be based on the standards - the minimum pitch is 0.6 m, the maximum is 1.2 m.
Calculation method
Produced this way.
— The length of the building is measured along the cornice.
— The resulting length is divided by the estimated distance between the rafters. For example, the estimated pitch of the rafters will be 0.8 m/p. (the average distance is considered to be 950 mm).
— After performing this action, you should add one to the result obtained and round the resulting amount. Thus, the required number of rafters is obtained on one side of the slope. After this, the length of the building must be divided by the number of rafters obtained, and as a result, the exact axial pitch of the rafters is determined.
Example, — building length 26.5 m/p. The distance between the rafters is supposed to be 0.8 m. This means:
– 26.5 m ˸ 0.8 m = 33.1 33.1+1 = 34.1. As a result, after rounding, it turns out that 34 rafters need to be installed on one slope.
26.5 m/p ˸ 34 Art. = 0.77 m - this value is the distance between the rafters along their central axes.
But that's only general methodology calculation that does not take into account the features of the planned roofing. Therefore, experts recommend calculating the pitch between the rafters for a certain roofing material and insulation, for example, for the most popular metal roofing tiles today.
Rafter structure for metal tiles
Metal tiles visually imitates ceramic roofing tiles. Made from thin sheet steel by cold stamping. Thanks to polymer coating, has high resistance to atmospheric influences and quite attractive visual appearance, not afraid of sudden temperature changes.
The advantage of metal tiles
Often used in the construction of most mansard roofs.
The cross-section of wooden rafters under a metal tile roof is usually standard 150-50 mm, but the distance between them can be from 600 mm, but not exceed 900 mm (depending on their angle of inclination, which can range from 22 to 45 degrees). This limitation of the pitch of the rafters is due to the fact that the sheathing under the metal tiles is mounted at a distance of 300 mm from each other. The standard timber used for sheathing has a cross-section of 30x50 mm or 50x50 mm. This means that each rafter is subject to additional load.
Stability of the roof structure against various mechanical loads depends on four factors:
An important factor when calculating the truss structure is is the estimated maximum load on the roof, the formation of which includes:
- The weight of the entire rafter structure.
- Weight of the sheathing under the covering.
- Weight of insulation and roofing.
- Snow load (determined using a special directory, unique for each individual region).
- Wind load (also according to a special directory for the region).
- Weight of a person with a tool ( renovation work, estimated weight - 175 kg/m²).
When installing the rafter system, the distance of the rafter legs should not exceed the average value of 0.9 m/p. except in certain cases provided for in advance.
If, when calculating the loads, there is any inaccuracy in the selection of material for the roof and the location of the rafters, its deformation and destruction of the roofing covering. Robust design the roof will be guaranteed only with the correct calculation of the cross-section of the rafters and their installation pitch.
It should be remembered. Universal meaning there is no calculation of rafter structures. When building each house, an individual calculation is required.
Rafters for a pitched roof
Shed roofs can often be found on small outbuildings. They can also be used on private residential buildings, but quite rarely. In such cases, the angle of inclination of the roof is quite small, and with this arrangement of the load-bearing floor beams, a lot of pressure is exerted on them, especially in winter.
Therefore, for a pitched roof, they are installed load-bearing beams ceilings made of large-section timber from 60x150 to 100x220 mm, depending on the width of the span to be covered. In this case, the distance at which the rafters are laid from each other should be in the range of 400 - 800 mm, depending on the angle of inclination of the roof.
For a pitched roof not required complex design rafters, they can simply be laid on the walls, without even using a Mauerlat. In regions where there are fairly snowy winters with a lot of snow, it is recommended to build the roof slope at a maximum angle of 35⁰ and position the roof in the direction of the “wind”. This reduces windage and leads to its self-cleaning.
Gable roof
It is a structure assembled from rafters connected to each other in the form of a triangle. Top part, which rests on the ridge, and the lower one on the mauerlats, located parallel to each other on opposite walls. In simple words, this is a roof consisting of two opposite slopes, connected by a ridge.
Gable roof structure, depending on its area, is mounted from separate rigid elements that enhance the strength of the roof. These include racks that support the rafters, ties that connect the rafters to each other, jibs, purlins, support beams, etc.
For gable roof, rafters are often installed taking into account the insulation in increments of 0.9 - 1.2 m/p. In this case, the strength of the mounted structure will be highest if the resulting triangle is isosceles. In regions with strong winds, it is recommended to install rafters with a slope of approximately 20⁰, and in snowy areas the optimal angle should be 45⁰.
Although the gable roof is considered classic, it has several alternative “related” types.
Mansard roof
For mansard roof , the calculated parameter for determining the pitch between the rafters and their number is taken to be a load in the range of 40-60 kg for every 1 m/p. rafters, and the maximum deflection from its length is 1/250. Usually, with a correctly selected section, this distance at the centers of the rafters is, as for a gable roof, 0.6 - 1.2 m/p.
It should be noted that the average load on the attic is approximately 200 kg/m2. So, when calculating the cross-section of rafters in a standard manner, it is recommended to add a small percentage of safety margin.
Hip roof
Among all truss structures, it is considered one of the most complex . It's practically hipped roof
, while the rafters of the end slopes are attached with their upper ends to the corner strings, and not to the ridge. Therefore, this type of roof may have its own specific requirements during construction. In this case, the rafters are installed similarly to a gable roof at a distance of 60 cm - 1.2 m/p.
Attic spaces under such a roof are built in rare cases, since its slopes “eat up” some area of the attic space, especially in height.
The distance between the rafters is a fundamental parameter on which the strength and reliability of the roof structure, its service life, and the possibility of using certain roofing materials depend.
The strength and service life of a roof depend on many factors: quality building materials, climatic conditions, reliability of the sheathing.
But the supporting structure of the roof is the foundation on which the entire structure rests.
The rafter system must be accurately calculated, correctly installed and reliably protected from destructive external influences.
General scheme for calculating rafter pitch
The rafter system is the supporting structure of the entire roof. It consists of rafter legs, vertical racks and inclined struts.
Each rafter is located at a certain distance from the next - this distance is called " rafter step».
The strength of the roofing structure depends on it, the maximum permissible load on square meter and materials that can be used for roofing work.
According to GOSTs, the minimum permissible value of the rafter pitch is 60 cm, the average is more than 1 m.
To determine the approximate step, you can use the following formula: D/(D/m+1), where D is the length of the roof from ridge to ridge, m is the approximate rafter pitch.
All results obtained must be rounded to the nearest higher integer. Obviously, this formula serves only for approximate calculations.
To determine the exact step size, the following factors must be taken into account:
- own weight of the rafter system, i.e. the materials from which it is made;
- the weight of the material with which you plan to cover the roof;
- weight of additional insulation, seals, hydro- and vapor barrier systems;
- sheathing weight;
- weight finishing materials attic;
- climatic loads (wind, snow accumulation).
In addition to the above loads, the roof must support the weight of at least one adult person, so that in the event of repairs or antenna installation, the installer can safely climb onto the roof.
If you are planning to install a chimney pipe, then its location must initially be included in the calculations so that in the future you will not need to remove part of the roof and install additional points supports.
Single-pitch and gable roof: the difference in rafter systems
For a pitched roof, erecting a rafter system is quite simple. Most often, rafters are laid directly on the crown, without the use of additional supports and supporting structures.
That is why the maximum angle of inclination of a pitched roof is limited to 30 degrees: the absence of additional load-bearing structures and support beams means that the entire load falls on the building walls and foundation.
The optimal tilt angle is 15 – 25 degrees. The maximum permissible rafter span length does not reach 6 m.
When erecting a pitched roof, be sure to take into account the direction of the wind and the possible additional load from the weight of snow accumulated on the roof.
For houses located in regions with strong winds and little precipitation, you can choose a slope angle at which the roof is cleared of snow due to gusts of wind.
A gable roof is a system of two inclined slopes connected by a ridge. One of the main advantages of this design is the possibility of more evenly distributing the load between the rafter system and the load-bearing walls of the building.
In addition, the gable frame allows the rafters to rest on each other, which gives it additional strength.
The overall strength of the roof structure increases as the slope angle approaches 45 degrees. It is this slope that is considered optimal for regions with heavy rainfall.
As the angle of inclination increases, on the one hand, stability increases significantly, so you can take a larger rafter pitch.
On the other hand, the windage of the roof increases, so for windy regions the optimal angle of inclination does not exceed 20 degrees.
Slate rafter system
Despite the appearance large selection modern roofing materials, classic version– slate – is still very popular, mainly due to its low cost and ease of installation.
The distance between roof rafters under slate is calculated taking into account the characteristics of the material: slate is quite fragile, but at the same time it can withstand heavy weight loads.
The permissible range of rafter pitch for slate is from 80 cm to 1.5 m. Most often, the average pitch length is used, 120 cm.
Since slate itself weighs quite a lot, the material for the supporting structure must be chosen durable, for example, beams with a cross-section of at least 75 mm by 150 mm.
The length of the rafter pitch and the thickness of the sheathing are interrelated: the stronger the sheathing you plan to install, the smaller step, and vice versa.
The slate sheet has standard length 175 mm, the sheathing pitch is selected in such a way that each slate sheet has at least three support points (one in the center of the sheet and two closer to the edges).
The sheathing pitch depends on the degree of roof slope: for a flat single- or gable roof, 63–67 cm is sufficient. The minimum gap for a steep roof is 45 cm.
You can establish the exact length of the rafter pitch for slate only by taking accurate measurements and calculating total weight all roofing materials.
Don’t forget to take into account weather conditions (possibility of snow accumulation, strong gusts of wind) and load additional equipment(antenna or chimney). If the attic will be equipped with an attic, then take into account the weight of the insulation.
Nuances of the system for metal tiles
Metal tiles are one of the most popular roofing materials on the market. It is easy to handle, durable, and looks beautiful.
In addition, metal tiles are one of the lightest roofing materials (only 35 kg per square meter); they can be laid on a fairly light support, thereby reducing the load on the building walls and foundation.
The average distance between the rafters for metal tiles is 60–95 cm for a gable roof with a slope of 20–45 degrees.
The size of the beams is chosen taking into account the insulation and waterproofing materials. For a simple metal roof, a cross-section of 50 – 150 mm is sufficient.
But in most cases, to create an attic roof, you will have to lay insulation 150 - 200 mm thick under the metal tiles.
Taking into account the weight of the insulation, the rafter system must be more durable; the recommended size of the beams increases to 200 mm by 50 mm.
When calculating the distance between the rafters, take into account not only the length of the metal tile sheets, but also the insulation.
At correct location rafters you can save significantly on timber.
Do not forget about the peculiarities of installing a roof made of metal tiles: this material does not allow air to pass through well, as a result of which condensation often accumulates under the roof.
Attach the top support of the rafter system to the ridge purlin instead of the side part. This will create a small air gap, will increase ventilation and help protect the roof from destructive moisture.
Rafter system for corrugated sheets and ondulin
Distinctive feature corrugated sheeting is light and rigid, therefore, as in the case of metal tiles, the requirements for the rafter system are not so high.
The distance between the rafters under the corrugated sheet should be in the range from 60 cm to 120 cm. The optimal cross-section of the rafter leg depends on the span between the supports.
So, for a span of 3 m, a beam measuring 40 mm by 150 mm is chosen, for a span of 5 m, a beam measuring 50 mm by 180 mm is chosen.
What distance is permissible between the rafter legs depends directly on the cross-section of the beams: the larger the rafter pitch, the more durable the material must be used for the rafters. When choosing a pitch of more than 80 cm, increase the thickness of the beams by 20 - 25%.
Do not forget to take into account the weight of the sheathing under the corrugated sheet. The distance between the rafters of a pitched roof of 60 cm will require sheathing with a minimum section of beams of 25 mm by 100 mm.
With a rafter pitch of 80 cm, it is 30 mm per 100 mm, etc. The angle of inclination of the roof also plays an important role: with a slope of less than 15 degrees, it is recommended to lay a continuous sheathing under the corrugated sheet, which is much heavier than the sparse one.
Because both are relatively light weight, the supporting structure can be quite light, reducing the load on the load-bearing walls and foundation of the building.
The higher the degree of inclination, the greater the distance between the rafters is allowed.
On a gable roof with a slope of less than 10 degrees, it is recommended to install continuous sheathing, which increases the load on the roof structure.
In this case, it is better to use a thicker beam measuring 40 mm by 50 mm, and reduce the rafter pitch to a minimum (60 cm).
The rafter structure is the fundamental element of a pitched roof. Incorrectly calculated distance between rafters, incorrect consideration of the load on the erected system of beams, or their incorrect installation will most likely lead to deformation and collapse. The stability of the rafter system depends on:
- from strength at the bottom to the ridge at the top;
- validity of the rafter support drawing, taking into account the span length;
- wood quality;
- pitch of the rafters.
- type of roofing material (metal tiles, slate, etc.);
- distance (span) between adjacent supports;
- the angle at which the rafter legs are attached.
Obviously, the main condition for the reliability of a roof structure is a correctly calculated distance between the rafters. You can figure out how to determine this value for a pitched, gable, or hip roof.
What are the calculations of span lengths based on?
A competent design calculation, in which the pitch of all rafter legs is calculated according to the same principle for any type of roof, is based on the following indicators:
- rafter weight;
- insulation weight;
- roof weight;
- sheathing weight;
- snow;
- wind;
the weight of a person or people who will subsequently be involved in repairs and maintenance of the roof itself and the objects located on it.
Snow and wind are different values for each region; you need to look for these indicators in reference information for a specific area or region.
How to calculate rafter spacing
The exact distance between the rafter legs is calculated using complex mathematical formulas, strength of materials, but many craftsmen cope with this task in their own way. After the calculation has been carried out maximum load, you should perform the following actions:
- measure the length of the roof;
- divide the result obtained by the span of the roof frame or the approximate step for installing the rafters (the pitch of the rafters is the distance from one leg to the other of the rafter system, usually a standard value, approximately selected, is taken into account);
- add one to the result obtained, round the resulting value;
After this, the length of the roof slope should be divided by the resulting value (the number of rafter trusses) - the desired rafter pitch will be obtained.
Calculation example. The ramp is 27m long, the selected pitch is 0.8m.
27:0,8=33,75
33,75+1= 34,75
round up = 35, the number 35 means that you need to install 35 rafters.
We determine the distance between the rafters: 27: 35 = 0.8. That is, the leg is installed one from the other at a distance of 80 cm.
The generally accepted standard is a value equal to 1 meter, and a step of eighty, seventy, ninety cm may also be optimal. Obviously, the calculation procedure cannot be called accurate, because the type of roofing material is not taken into account.
Intervals between rafters used for different types of roofing materials
When calculating the pitch of the rafter legs, it is necessary to take into account the characteristics and dimensions of the roofing material. The following types of roofing can be considered the most popular:
- corrugated sheeting;
- ceramic tiles;
- metal tiles;
- ondulin;
- slate.
These types of roofing are used for roof installation residential buildings, baths, outbuildings. For each type of roof and roof shape, pitched, gable or otherwise, a certain gap between the rafters is used.
Corrugated sheet
Corrugated sheeting is a modern, durable material made from galvanized sheets formed into a specific profile. Lightweight material, durable. When using it, the calculation of the distance between adjacent rafters is 60-90 centimeters. A larger distance is only possible if there is a large cross-section board fastening the rafters. The sheathing for corrugated sheeting is made from a board of thirty, mounted 50 cm apart from each other; if the roof angle is 15°, the corrugated sheet is laid on the sheathing, laid without gaps.
The pitch of the rafters under the corrugated sheet does not depend on its brand. So, C44 is the most heavy material They are attached to the lathing with a span of 30 cm, but the pitch of the rafters does not change.
Ceramic tiles
Calculation of the pitch of rafter beams for ceramic tiles, a heavy, expensive material, is somewhat different from others. For material that weighs a lot, only dried strong beams with a section of 50x150, 60x180 cm are used. The optimal distances between rafters, accepted as standards, range from 80 to 120 cm. The choice of interval depends on the slope and type of roof. The calculation must be made taking into account the length rafter beam. The longest rafter requires a minimum step and, conversely, the short length of the rafter allows the use of a step of maximum width.
Metal tiles
Metal tiles can easily be called the leader among all roofing materials. It is used for complex, hip, gable, hip, and pitched roofs. Its installation is much simpler than ceramic tiles. Metal tiles can be placed on old roof, replace ceramic tiles, slate, using the old step. Metal tiles are 10 times smaller, so they use beams of a smaller section 50x150, the pitch between the rafters is from 60-90 cm, standard values. It is especially convenient to insulate such a roof by including the width of roll or sheet insulation in the calculation.
Ondulin
This type of soft roof is becoming increasingly popular, lightweight, easy to install, strong and durable. Sheets of ondulin are attached in an overlap to a 40x50 sheathing made of boards coniferous species trees (step 60 cm).
The pitch of the rafter legs is from 60 to 90 cm. Beams are needed with a section of 50x150 or 50x200.
Slate
Slate is widely used to cover outbuildings, bathhouses, houses, and garages. Therefore, many people know what the distance between the rafters should be when using this roofing material. The use of this particular material created a system of rafter spacing 60-80, battens 50x50. The sheathing is made from 50x50 bars or a thirtieth board, depending on the slope. For a flat pitched roof, a sheathing pitch of 45 cm is used, for a gable roof - 65 cm.
How do the pitches of the rafters of gable and lean-to roofs differ?
Each type of roof has its own strength. The pitch of the rafter beams depends on what safety margin should be included when installing a particular type of roof.
Single-pitched roof structures, which are typical for simple buildings for household purposes, made from beams mounted on walls. The distance between roof rafters directly depends on their length. It is also important to take into account the cross-section of the timber used, based on the fact that the longer the gap, the greater the load.
The gable system, which includes gable, hip, hip and other structures, is always installed with thermal insulation. The standard pitch for such roofs is 1-1.2 meters. In each specific case, the calculation is carried out taking into account, as already mentioned, the weight of the roofing material and other things, SNiP 2.01.85 is taken as the basis, which considers all types of loads and impacts. The step is calculated according to the usual scheme given above. The angle of inclination must be taken into account. The 45° angle allows the use of all types of roofing. For identical roof slopes, the pitch of one side is calculated.
Follow these tips:
- If a decision is made to independent arrangement roofing, check the accuracy of your calculations with specialists or, at worst, use the services online calculators construction companies.
- When determining the pitch of the rafters, remember about thermal insulation; any roll or sheet insulation shrinks over time. Remember about ventilation holes, waterproofing.
- If the roof slope is 45° or more, the weight of a person is subtracted from the maximum load, which allows the use of fewer rafters (by 20%).
- Decide what type: layered or required for the selected roof geometry.
- Take your time when choosing a timber; it must be dry (residual moisture no more than 20%), made from coniferous wood.
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
The development of a project for a single-pitch or gable roof begins with choosing the type of rafter system, the angle of inclination of the slopes (roof height) and materials for constructing the structure. Calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Constant loads include:
- the weight of the materials from which the rafter system is made;
- roofing weight;
- weight of roofing materials (waterproofing, vapor barrier, insulation);
- weight of finishing elements of a residential attic or attic.
In addition to permanent loads, the roof also experiences temporary loads, which include:
The pitch refers to the distance between the rafters of one slope. When calculating a single-pitch, gable or complex roof, we usually adhere to 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 pitch cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the features of installing the sheathing for various types of roofing material. If a roof with a chimney is being designed, the pitch can be adjusted taking into account its location, so that you do not have to subsequently remove part of the rafters and install a supporting structure, such as a special rafter system.
Distance between rafters under slate
Slate is a traditional roofing material. Its advantages include characteristics such as resistance to external influences (excluding mechanical) and low cost. Slate allows you to create a roofing covering, the repair of which can be reduced to replacing individual elements. Slate is heavy and requires the installation of a fairly powerful rafter system. Calculation of the distance at which it is necessary to place the rafters under the slate is carried out taking into account the cross-section of the beam for the manufacture of rafter legs.
The optimal solution is to install a system under slate, in which the gap between the rafters should be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the sheathing is made of timber or boards with a cross-section of at least 30 mm. When calculating a rafter system for slate, you should read that this material has quite large restrictions on the choice of the angle of inclination of the slopes.
Rafters for metal tiles
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a pitched, gable, hip or complex roof. The frame for metal tiles is built according to standard principles. To calculate at what distance it is better to install the rafters, it is necessary to take into account the loads and the angle of the roof. Metal tiles are characterized by their relatively low weight, thanks to which they can serve as a replacement for old slate or ceramic tile roofing. In this case, the rafters will not need to be strengthened or the pitch of their installation changed.
The standard pitch of rafters for metal tiles is 600-900 mm. The cross-section of the elements can be 50-150 mm - this is enough to create a reliable frame for metal tiles. But if you plan to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use 200x50 timber for rafters under metal tiles, so as not to install an additional system that holds 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 sheeting can be used both for installing a single-pitched roof for a utility room or garage, and for a gable roof of a residential building. How to calculate the distance required to install rafters under corrugated sheeting?
To ensure the necessary structural rigidity, it is enough to install the rafters under the corrugated sheets in increments of 600-900 mm. In this case, you need to pay attention to the angle of the roof. Calculations show that under high external loads, it is better to lay corrugated sheets on the system with a minimum step. But if the distance between the rafters under the corrugated sheet is close to the maximum, and the roof slope angle is small, then the structure is strengthened by using more frequent sheathing. In this case, the pitch of the sheathing under the corrugated sheet should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofing includes bitumen and bitumen-polymer roll materials, roofing membranes, 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 supports under a 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 of the insulating material to simplify its installation. This calculation allows you to reduce the financial costs of roofing.
Sandwich panel roof
Sandwich roofing is most often erected on houses made of sip panels or hangar-type buildings. A special feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the top of the wall (or the distance between the supporting structures of a gable roof) allow the installation of a sandwich without additional supports.
If the span exceeds 4 meters, additional purlins must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case, the rafters can be positioned at larger intervals - they serve as a support for the purlins. The distance between the rafter legs is selected based on the length of the available material for the purlins and the length of the load-bearing walls. The technical parameters of the sandwich allow the roof to withstand high operating loads.
Polycarbonate: construction of a supporting structure
Polycarbonate has recently been actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, canopies, and winter gardens. The lathing and rafter system for polycarbonate can be made of wood or metal.
Polycarbonate varies in weight depending on the thickness of the sheet. It is recommended to perform lathing under polycarbonate in increments of 600-800 mm. The lathing (wooden or metal) is mounted on rafters, which can be straight or arched. Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to lower the rafters, it is necessary to take into account the glazing area, the size and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.
The distance between the rafters of a gable and pitched roof
Find out what distance between the rafters needs to be made for a gable and shed roof. 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
A 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.
Also, the quality of the structure is affected by the fastening of the rafters to the Mauerlat and ridge run. 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
Distance between rafter legs gable roof 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 on which ceramic tiles or asbestos-cement slate were previously laid.
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 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.
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 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.
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 you place insulation with a thickness of 150 mm in the space between the rafters, then attic will be created the most 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.
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.
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 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, 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.
