Rafter is one of the individual elements load-bearing structure 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 with a section of 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 that long time will be a high-quality support for the roof.
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 optimal distance between the rafters for the roof, The following parameters are taken as a basis:
- Type of roof covering.
- View of the rafter system and design features of the roof.
- 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 complex broken roof With large area, most likely, it will not be possible to do this 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 a rather attractive visual appearance, and is 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. Standard timber, which is used for lathing, has a cross-section of 30x50 mm or 50x50 mm. This means that each rafter is subject to additional load.
Sustainability roofing 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 by a special, unique for each separate region, reference book).
- 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 value calculation truss structures does not exist. When building each house, an individual calculation is required.
Rafters for a pitched roof
Shed roofs can often be found in 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 pitched roof 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. The upper part, which rests on the ridge, and the lower part 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 a 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 optimal angle should be 45⁰.
Although the gable roof is considered classic, it has several alternative “related” types.
Mansard roof
For mansard roof , behind design parameter to determine the pitch between the rafters and their number, a load of 40-60 kg for every 1 m/p is accepted. 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 requirements during construction. certain requirements. In this case, the rafters are installed similarly to a gable roof at a distance of 60 cm - 1.2 m/p.
Attic rooms under such a roof are made in rare cases, since its slopes “eat up” some area attic space, especially in height.
A gable roof is formed on the basis of a frame that combines the simplicity of the device and unsurpassed reliability. But the roof skeleton of two rectangular slopes can boast of these advantages only if the rafter legs are carefully selected.
Parameters of the gable roof rafter system
You should start making calculations if you understand that the rafter system gable roof- this is a complex of triangles, the most rigid elements of the frame. They are assembled from boards, the size of which plays a special role.
Rafter length
The formula will help determine the length of durable boards for the rafter systema²+b²=c², derived by Pythagoras.
The length of the rafter can be found by knowing the width of the house and the height of the roof
The parameter “a” indicates the height and is independently selected. It depends on whether the under-roof space will be residential, and also has certain recommendations if an attic is planned.
Behind the letter "b" is the width of the building, divided in two. And “c” represents the hypotenuse of the triangle, that is, the length of the rafter legs.
Let’s assume that the width of half the house is three meters, and it was decided to make the roof two meters high. In this case, the length of the rafter legs will reach 3.6 m (c=√a²+b²=4+√9=√13≈3.6).
You should add 60–70 cm to the figure obtained from the Pythagorean formula. The extra centimeters will be needed to carry the rafter leg beyond the wall and make the necessary cuts.
The six-meter rafter is the longest, so it is suitable as a rafter leg
The maximum length of a beam used as a rafter leg is 6 m. If a durable board of greater length is required, then they resort to the fusion method - nailing a section from another beam to the rafter leg.
Section of rafter legs
For various elements rafter systems have their own standard sizes:
- 10x10 or 15x15 cm - for mauerlat timber;
- 10x15 or 10x20 cm - for the rafter leg;
- 5x15 or 5x20 cm - for purlin and bracing;
- 10x10 or 10x15 cm - for a stand;
- 5x10 or 5x15 cm - for a bed;
- 2x10, 2.5x15 cm - for laths.
The thickness of each part of the supporting roof structure is determined by the load that it will experience.
A beam with a section of 10x20 cm is ideal for creating a rafter leg
The cross-section of the rafter legs of a gable roof is affected by:
The most significant effect on the cross-section of the rafter legs is the pitch of the rafters. An increase in the distance between the beams entails increased pressure on the supporting structure of the roof, and this obliges the builder to use thick rafters.
Table: rafter cross-section depending on length and pitch
Variable impact on the rafter system
The pressure on the rafter legs can be constant or variable.
From time to time and with varying intensity, the supporting structure of the roof is affected by wind, snow and precipitation. In general, the roof slope is comparable to a sail, which can break under the pressure of natural phenomena.
The wind tends to overturn or lift the roof, so it is important to make all the calculations correctly
The variable wind load on the rafters is determined by the formula W = Wo × k x c, where W is the wind load indicator, Wo is the value of the wind load characteristic of a certain area of Russia, k is a correction factor determined by the height of the structure and the nature of the terrain, and c is the aerodynamic factor coefficient.
The aerodynamic coefficient can vary from -1.8 to +0.8. A negative value is typical for a rising roof, while a positive value is typical for a roof on which the wind presses. In a simplified calculation with a focus on improving strength, the aerodynamic coefficient is considered equal to 0.8.
Calculation of wind pressure on the roof is based on the location of the house
The standard value of wind pressure is determined from map 3 of Appendix 5 in SNiP 2.01.07–85 and a special table. The coefficient taking into account the change in wind pressure with height is also standardized.
Table: standard value of wind pressure
Table: k coefficient value
It's not just the terrain that affects wind loads. Great importance has a residential area. Behind a wall of tall buildings there is almost no threat to the house, but in an open space the wind can become a serious enemy for it.
The snow load on the rafter system is calculated using the formula S = Sg × µ, that is, the weight of the snow mass per 1 m² is multiplied by a correction factor, the value of which reflects the degree of roof slope.
The weight of the snow layer is indicated in SNiP “Rafter Systems” and is determined by the type of terrain where the building is built.
The snow load on the roof depends on where the house is located
The correction factor, if the roof slopes tilt less than 25°, is equal to one. And in the case of a roof slope of 25–60°, this figure decreases to 0.7.
When the roof is sloped more than 60 degrees, the snow load is discounted. Still, snow rolls off a steep roof quickly, without having time to negative influence to the rafters.
Constant loads
Continuously acting loads are considered to be the weight of the roofing pie, including sheathing, insulation, films and finishing materials for the attic.
The roofing pie creates constant pressure on the rafters
The weight of the roof is the sum of the weight of all materials used in the construction of the roof. On average it is 40–45 kg/sq.m. According to the rules, 1 m² of rafter system should not have more than 50 kg of weight roofing materials.
To ensure that there is no doubt about the strength of the rafter system, it is worth adding 10% to the calculation of the load on the rafter legs.
Table: weight of roofing materials per 1 m²
| Type of roofing finish | Weight in kg per 1 m² |
| Rolled bitumen-polymer sheet | 4–8 |
| Bitumen-polymer soft tiles | 7–8 |
| Ondulin | 3–4 |
| Metal tiles | 4–6 |
| Corrugated sheeting, seam roofing, galvanized metal sheets | 4–6 |
| Cement-sand tiles | 40–50 |
| Ceramic tiles | 35–40 |
| Slate | 10–14 |
| Slate roofing | 40–50 |
| Copper | 8 |
| Green roof | 80–150 |
| Rough flooring | 18–20 |
| Lathing | 8–10 |
| The rafter system itself | 15–20 |
Number of beams
How many rafters will be needed to arrange the frame of a gable roof is determined by dividing the width of the roof by the pitch between the beams and adding one to the resulting value. It indicates an additional rafter that will need to be placed on the edge of the roof.
Let's say it was decided to leave 60 cm between the rafters, and the length of the roof is 6 m (600 cm). It turns out that 11 rafters are needed (including the additional timber).
The rafter system of a gable roof is a structure made from a certain number of rafters
The pitch of the beams of the supporting roof structure
To determine the distance between the beams of the supporting roof structure, you should pay close attention to such points as:
- weight of roofing materials;
- the length and thickness of the beam - the future rafter leg;
- degree of roof slope;
- level of wind and snow loads.
It is customary to place rafters at 90–100 cm intervals when choosing a lightweight roofing material
A normal step for rafter legs is 60–120 cm. The choice in favor of 60 or 80 cm is made in the case of constructing a roof inclined at 45˚. The same small step should be taken if you want to cover the wooden roof frame with heavy materials such as ceramic tiles, asbestos-cement slate and cement-sand tiles.
Table: rafter pitch depending on length and cross-section
Formulas for calculating the rafter system of a gable roof
Calculation of the rafter system comes down to establishing the pressure on each beam and determining the optimal cross-section.
When calculating the rafter system of a gable roof, proceed as follows:
- Using the formula Qr=AxQ they find out what the load on linear meter each rafter leg. Qr is the distributed load per linear meter of a rafter leg, expressed in kg/m, A is the distance between the rafters in meters, and Q is the total load in kg/m².
- Proceed to determining the minimum cross-section of the rafter beam. To do this, study the data from the table included in GOST 24454–80 “Lumber coniferous species. Dimensions".
- Focusing on standard parameters, select the section width. And the section height is calculated using the formula H ≥ 8.6 Lmax sqrt(Qr/(BRbend)), if the roof slope is α< 30°, или формулу H ≥ 9,5·Lmax·sqrt(Qr/(B·Rизг)), когда уклон крыши α >30°. H is the height of the section in cm, Lmax is the working section of the rafter leg of maximum length in meters, Qr is the distributed load per linear meter of the rafter leg in kg/m, B is the section width cm, Rbend is the bending resistance of wood, kg/cm². If the material is made from pine or spruce, then Ri can be equal to 140 kg/cm² (grade 1 wood), 130 kg/cm² (grade 2) or 85 kg/cm² (grade 3). Sqrt is the square root.
- Check whether the deflection value complies with the standards. She shouldn't be more numbers, which is obtained by dividing L by 200. L refers to the length of the working section. Correspondence of the deflection value to the ratio L/200 is feasible only if the inequality 3.125·Qr·(Lmax)³/(B·H³) ≤ 1 is true. Qr denotes the distributed load per linear meter of the rafter leg (kg/m), Lmax is the working section of the rafter leg maximum length (m), B is the section width (cm), and H is the section height (cm).
- When the above inequality is violated, the indicators B and H increase.
Table: nominal dimensions of thickness and width of lumber (mm)
| Board thickness - section width (B) | Board width - section height (H) | ||||||||
| 16 | 75 | 100 | 125 | 150 | - | - | - | - | - |
| 19 | 75 | 100 | 125 | 150 | 175 | - | - | - | - |
| 22 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | - | - |
| 25 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 32 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 40 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 44 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 50 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 60 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 75 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 100 | - | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 |
| 125 | - | - | 125 | 150 | 175 | 200 | 225 | 250 | - |
| 150 | - | - | - | 150 | 175 | 200 | 225 | 250 | - |
| 175 | - | - | - | - | 175 | 200 | 225 | 250 | - |
| 200 | - | - | - | - | - | 200 | 225 | 250 | - |
| 250 | - | - | - | - | - | - | - | 250 | - |
Example of load-bearing structure calculation
Let us assume that α (roof inclination angle) = 36°, A (distance between rafters) = 0.8 m, and Lmax (working section of the rafter leg of maximum length) = 2.8 m. First grade pine material is used as beams , which means that Rben = 140 kg/cm².
Cement-sand tiles were chosen to cover the roof, and therefore the weight of the roof is 50 kg/m². Total load (Q) experienced by each square meter, equal to 303 kg/m². And for the construction of the rafter system, beams 5 cm thick are used.
The following computational steps follow from this:
- Qr=A·Q= 0.8·303=242 kg/m - distributed load per linear meter of rafter beam.
- H ≥ 9.5 Lmax sqrt(Qr/BRbend).
- H ≥ 9.5 2.8 sqrt(242/5 140).
- 3.125·Qr·(Lmax)³/B·H³ ≤ 1.
- 3.125·242·(2.8)³ / 5·(17.5)³= 0.61.
- H ≥ (approximate height of the rafter section).
In the table of standard sizes, you need to find a section height of the rafters that is close to 15.6 cm. A suitable parameter is 17.5 cm (with a section width of 5 cm).
This value is quite consistent with the deflection in regulatory documents, and this is proven by the inequality 3.125·Qr·(Lmax)³/B·H³ ≤ 1. Substituting the values (3.125·242·(2.8)³ / 5·(17.5)³) into it, we find that 0.61< 1. Можно сделать вывод: сечение пиломатериала выбрано верно.
Video: detailed calculation of the rafter system
Calculating the rafter system of a gable roof is a whole complex of calculations. In order for the beams to cope with the task assigned to them, the builder needs to accurately determine the length, quantity and cross-section of the material, find out the load on it and find out what the pitch between the rafters should be.
The single-pitched rafter system came to us from the USA and Europe. Residents using it noted its reliability and low cost, so the popularity of this type spread very quickly. Despite the fact that a small amount of wood was required to build one slope, few people dared to undertake such construction. The fact is that most developers considered such a system too simple for residential buildings, and the other part simply did not know how to build it, in order to prove the opposite. In this article I will try to explain to you how to easily and quickly create such systems and correctly select the pitch of the rafters of a pitched roof.
Basis of calculations
Despite its simplicity, one slope must meet all installation rules. After all, if we allow serious mistakes, That roof covering deformed, which will inevitably lead not only to leaks, but also to the collapse of the entire roof.
For maximum stability roofing system It is necessary to pay attention to four components:
- Reliability of fastening the rafter legs to the support beam and ridge;
- Correct selection of auxiliary parts for the rafter system;
- Durable lumber and auxiliary elements;
- Rafter step.
Don’t think that by observing just four points you will achieve the most stable structure. To do this, you will have to use all known methods and technologies.
Values for calculations
You can’t perform calculations without knowing certain indicators, right? So before you start, you need to make sure you have four basic values.
In addition to all these indicators, the main task of any project is to calculate the maximum permissible load on the roof. It includes quite a lot of values and here is a list of elements whose mass is especially important in the calculation:
- Rafter legs
- Lathing
- Roofing pie
If you are far from the construction industry, then you will have to remember that the calculation maximum load The roof consists of two parts. The first takes into account all the materials used, and the second contains the snow load of your region. Its meaning is written in a special reference book, which you can easily find on the Internet.
But even this indicators will not be accurate, because you forgot about the wind load and the weight of the worker who will carry out the work. installation work and subsequent maintenance (repair, cleaning).
When developing a project construction organization they use complex formulas resistance, so if you don’t want to worry about this, you can use the recommendations of experienced people.
How to calculate the required distance between rafter beams
The distance between the rafters of a pitched roof largely depends on the pre-calculated maximum possible pitch. To identify given value you will need to matter total load, roof parameters and data on the wood of the rafters.
You can calculate the optimal pitch of the rafter leg using the following method:
- First of all, you need to find the full length of the roof. This value should include any ends and overhangs;
- Divide the resulting value by the maximum permissible distance between the rafters;
- We round the answer up. This number will indicate the number of spans;
- Next, take the roof length and divide it into spans. This way you will find the optimal step;
- And to find the number of rafter legs, you need to add one to the spans.
This rule works for the vast majority of roofs, but there are also those that cannot be calculated in this way. If this is your case, you will have to get an additional rafter at one of the ends. 
Rafter system depending on roofing covering
It's no secret that the greater the mass of the roof covering, the greater the number of rafter legs that need to be installed. Most manufacturers of this material in the instructions for its product it indicates the optimal number of rafters and their sizes.
You should not blindly trust these instructions unless you live in the central part of Russia, because they were written specifically for this territory. Before developing a drawing, it is necessary to carefully study the prevailing winds and draw a kind of rose, which will serve as a guide for future construction.
It is worth noting that in regions of the country where it falls a large number of precipitation in the form of snow, it is best to create steep roofs with a slope slope of 35-45 degrees. This will provide fast natural gathering snow cover from the surface.
In most cases, the rafter system of private houses is created from logs with a diameter of 12 to 22 centimeters, timber or boards with thicknesses from 40 to 100 and widths from 150 to 220 millimeters.
Rafter system for corrugated sheets
Roofing corrugated sheets lightweight material and at the same time has good strength characteristics. Therefore, small-section lumber can be used as rafter legs, but with frequent steps: 0.6 - 1.2 meters. The roof slope should be at a slope of 12 to 45 degrees.
The required cross-section can be selected based on the span distance between the supports. If the distance is about 3 meters, then the cross-section can be 40x150 millimeters, at 4 meters this value increases to 50x180 millimeters, and at 6 meters it is necessary to use lumber with a cross-section of 60x200 millimeters.
By the way, the lathing also plays an important role in this matter. In the case where the rafter pitch is a decent value, you will have to use more wide boards. For example, for a step of 0.6 meters you will need elements with a cross-section of 25x100 millimeters, and for 1.2 meters - 40x100.
Lathing for corrugated sheets is arranged discharged method, and the pitch of its elements should be 50-80 centimeters. However, these values may go beyond due to the characteristics of the roofing itself. You can also find tips on how to arrange these parts in the instructions included with the purchased material.
Rafter system for ceramic tiles
Ceramic tiles are a unique roofing covering. It is made of clay, which makes this material very heavy. Designed rafter systems in mandatory must follow the following requirements:
In the roofing industry, there are only 3 types of sheathing. One of them can be arranged at an angle of 12-60 degrees, and the other two at 20-45 degrees. As sheathing elements for clay tiles, you can most often see timber with a cross-section of 50x50 millimeters.
Rafters for metal tiles
Due to the fact that metal sheets are significantly thinner, you do not have to install a serious rafter system. Therefore, you can safely follow the advice and recommendations of roofing material manufacturers.
It’s worth saying a few words about the only nuance that will allow you to save some lumber. So, it lies in the fact that the minimum pitch of the sheathing can be increased to 1 meter. This is due to the size sheet material. When a metal tile is tripled, as a rule, it is supported by sheathing only in a few places, and with a rafter pitch of 0.6 meters, it is impossible to create an “economical” sheathing, so you have to change it along with the rafter system. 
Rafter structure for ondulin
Today, ondulin has given way to more modern coatings, but despite this, developers whose roofs were laid with asbestos slate began to look at this material as a profitable alternative. It is made on the basis of bitumen and fiberglass, is lightweight and of high quality.
The rafter system for ondulin must meet the following parameters:
- The slope of the slope should be in the range from 5 to 45 degrees;
- With a small slope, the pitch of the rafter legs should be minimal: 0.6 meters, and with a steeper roof this distance increases to 0.9 meters;
- With a flat roof, say up to 10 degrees, it is necessary to arrange a continuous sheathing. The best way to do this is to use moisture resistant plywood, OSB boards or edged board with a section of 30x100 or timber 40x50 millimeters.
As for the cross-section of the rafter legs themselves, it is selected according to the same rules as for corrugated sheeting.
Rafter system for corrugated asbestos-cement sheets (slate)
Surprisingly, everyone knows the roofing material called “slate”, because the vast majority of private houses are covered with this particular product. Due to its rigidity and components, this material has quite a significant weight, so it is necessary to follow the recommendations for the construction of the rafter system so that it does not collapse even before the start of operation.
- The low tightness of the finished plane does not allow the use of slate with a slope slope of less than 22 degrees, this will lead to leaks. If you cannot find any recommendations for installing asbestos-cement sheets (which is unlikely), then you always have the right to use the instructions included with the ondulin;
- The maximum possible slope of the rafters with a slate roof is less than 60 degrees;
- The optimal pitch of the rafter legs is in the range from 0.8 to 1.5 meters. Here everything will depend on the load and cross-section of the lumber;
- As a rule, a wooden system under slate requires a slightly larger section of legs than with a light roof. As an example, we can cite a situation where the pitch of the rafters is 1.2 meters. For the rafters you will have to take a beam with a section of 75x150 or 100x200;
- As for the sheathing, its elements will also differ from the pitch of the rafter legs. If it is up to 1.2 meters, then a beam of 50x50 millimeters will do just fine, and if larger step– 60x60 millimeters;
- The pitch of the sheathing beam should be selected so that one sheet is supported by 3 elements. The slate should extend 15 centimeters beyond the edges on both sides. For example, if we consider standard sizes asbestos cement sheet(175 centimeters), then you can use a sheathing pitch of 80 centimeters.
It's probably worth remembering that asbestos is harmful substance Therefore, when working with a material that contains its particles, safety precautions must be observed. Which states that the worker must have personal protective equipment with him. 
Rafter system of one and two slopes
IN Lately the pitched roof is gaining more and more popularity. This is understandable, because materials are only becoming more expensive, and you really want to save money. Thanks to a simple design this can be done. The rafter system of one slope is quite primitive. To do this, you just need to place the beams on the crown and secure them. Of course, do not forget about the insulating material.
The maximum slope of a pitched roof can be 30 degrees, and the span can be 6 meters (this rule applies to lumber). The most optimal slope is considered to be 15-20 degrees. At this angle, the wind load will not cause much harm, but the snow cover will cause some inconvenience. The solution to this problem may be to place your building “downwind”, which will allow it to remove snow mass from the roof naturally.
Alternative option pitched roof is gable. It consists of a number of rectangles connected together using a Mauerlat and a ridge. One thing worth noting interesting fact. When the shape of a triangle approaches an isosceles one, its rigidity increases. In this regard, with a roof slope of up to 60 degrees, it is possible to expand the pitch between the rafters.
But you shouldn’t play around with calculations, because this can lead to an increase in windage and consumption of lumber. The most optimal slope of the slopes for a gable system is 45 degrees.
If you decide to build the roof yourself, then you will probably need some tips that will not only make your work easier, but also increase operational period your roof as a whole.
- Calculating the structure correctly is not an easy task, but even if it is done correctly, it can be damaged if it is fastened incorrectly. Therefore, when installing the rafter legs in their places, perform the work with all responsibility. To improve your skills, you can read information on the Internet, or invite a knowledgeable person to the site;
- The pitch of the rafter legs should not affect the thermal insulation in any way. It is worth remembering that the slabs can change slightly in size. Take advantage of this and squeeze them in as tightly as possible. In a hardware store, there are standard sizes of insulation boards of 60, 80, 100 and 120 centimeters;
- For most roofs with a slope of less than 45 degrees, it is necessary to include the worker's weight in the calculation. As for sharper roofs, this is not necessary; therefore, the pitch of the rafter legs can be reduced by 20%;
- Take advantage modern technologies and calculate your roof using online calculators. All you need to do is enter the exact parameters;
- Regulatory documents regarding wind and snow load you can find it online or from construction workers;
- Any wood used for construction purposes should be dried as much as possible. This will avoid its deformation in the future.
The roof of a building is one of the most important elements the entire building. If you start saving on roofing pie, then you will soon face expensive repairs that will affect not only this area, but the entire building as a whole. Therefore, if you want to get the maximum service life from your comfort, then you should not use low-quality materials.
Other name gable variety roofs are gable.
She has two identical inclined surfaces.The roof frame structure is represented by a rafter system.
In this case, pairs of rafters leaning against each other are united by sheathing. Triangular walls, or tongs in other words, are formed at the ends.
A gable roof is quite simple .
At the same time very important point For installation it is necessary to correctly calculate the required parameters.
IN rafter system the attic has the following elements:
- Mauerlat. This element serves as the basis for the entire roof structure and is attached along the perimeter of the walls from above.
- Rafters. Boards certain size, which are attached at the required angle and have support in the Mauerlat.
- Horse. These are the designations of the place where the rafters meet at the top.
- Crossbars. They are located in a horizontal plane between the rafters. Serve as a coupling element for the structure.
- Racks. Supports that are placed in a vertical position under the ridge. With their help, the load is transferred to load-bearing walls.
- Strut. Elements located at an angle to the rafters to divert the load.
- Sill. Similar to the Mauerlat, only located on the internal load-bearing floor.
- Fight. A block placed vertically between supports.
- . Structure for roof installation.
Calculation of the rafter system of a gable roof - online calculator
Field designations in the calculator
Specify roofing material:
Select a material from the list -- Slate (corrugated asbestos cement sheets): Medium profile (11 kg/m2) Slate (corrugated asbestos cement sheets): Reinforced profile (13 kg/m2) Corrugated cellulose-bitumen sheets (6 kg/m2) Bitumen (soft , flexible) tiles (15 kg/m2) Galvanized sheet metal (6.5 kg/m2) Sheet steel (8 kg/m2) Ceramic tiles (50 kg/m2) Cement-sand tiles (70 kg/m2) Metal tiles, corrugated sheets (5 kg/m2) Keramoplast (5.5 kg/m2) Seam roofing (6 kg/m2) Polymer-sand tiles (25 kg/m2) Ondulin (Euro slate) (4 kg/m2) Composite tiles(7 kg/m2) Natural slate (40 kg/m2) Specify the weight of 1 square meter of coating (? kg/m2)
kg/m2
Enter the roof parameters (photo above):
Base width A (cm)
Base length D (cm)
Lifting height B (cm)
Length of side overhangs C (cm)
Front and rear overhang length E (cm)
Rafters:
Rafter pitch (cm)
Type of wood for rafters (cm)
Work area side rafter(optional) (cm)
Lathing calculation:
Sheathing board width (cm)
Sheathing board thickness (cm)
Distance between sheathing boards
F (cm)
Calculation of snow load (pictured below):
Select your region
1 (80/56 kg/m2) 2 (120/84 kg/m2) 3 (180/126 kg/m2) 4 (240/168 kg/m2) 5 (320/224 kg/m2) 6 (400/280 kg/m2) 7 (480/336 kg/m2) 8 (560/392 kg/m2)
Wind load calculation:
Ia I II III IV V VI VII
Height to the ridge of the building
5 m from 5 m to 10 m from 10 m
Terrain type
Open area Closed area Urban areas
Calculation results
Roof angle: 0 degrees.
The angle of inclination is suitable for this material.
It is advisable to increase the angle of inclination for this material!
It is advisable to reduce the angle of inclination for this material!
Roof surface area: 0 m2.
Approximate weight roofing material: 0 kg.
Number of rolls insulating material with 10% overlap (1x15 m): 0 rolls.
Rafters:
Load on the rafter system: 0 kg/m2.
Rafter length: 0 cm
Number of rafters: 0 pcs.
Lathing:
Number of rows of sheathing (for the entire roof): 0 rows.
Uniform distance between sheathing boards: 0 cm
Number of sheathing boards with a standard length of 6 meters: 0 pcs.
Volume of sheathing boards: 0 m3.
Approximate weight of sheathing boards: 0 kg.
Snow load region
Description of calculator fields
It is quite simple to make all the calculations before starting work on building a roof. The only thing is what is required is scrupulousness and attentiveness, You should also not forget about checking the data after completing the process.
One of the parameters that cannot be avoided during the calculation process is total area roofs. You should initially understand what this indicator represents in order to better understand the entire calculation process.
There are some general provisions which are recommended to be followed during the calculation process:
- The first step is to determine the length of each slope. This value is equal to the intermediate distance between the points at the very top (on the ridge) and at the bottom (the cornice).
- Calculating such a parameter it is necessary to take into account all additional roofing elements, for example, overhang and any kind of structures that add volume.
- At this stage also the material must be specified, from which the roof will be constructed.
- No need to consider when calculating the area of ventilation and chimney elements.
ATTENTION!
The above points apply in the case of a regular roof with two slopes, but if the house plan assumes the presence of an attic or another type of roof shape, then it is recommended to carry out calculations only with the help of a specialist.
The rafter system calculator will best help you with your calculations. gable roof.
Calculation of the rafter system of a gable roof: calculator
Calculation of rafter parameters
Push off in in this case need from a step, which is selected individually taking into account the roof structure. This parameter is influenced by the selected roofing material and the total weight of the roof.
This indicator can vary from 60 to 100 cm.
To calculate the number of rafters you need:
- Find out the length of the slope;
- Divide by the selected step parameter;
- Add 1 to the result;
- For the second slope, multiply the indicator by two.
The next parameter to determine is the length of the rafters. To do this, you need to remember the Pythagorean theorem, this calculation is based on it. The formula requires the following data:
- Roof height. This value is chosen by everyone individually, depending on the need to equip a living space under the roof. For example, this value will be equal to 2 m.
- The next value is half the width of the house, in this case – 3m.
- The quantity that needs to be known is hypotenuse of the triangle. Having calculated this parameter, starting from the example data, we get 3.6 m.
Important: to the result obtained for the length of the rafters, you should add 50-70 cm, taking into account the cut.
Besides, you should determine what width to choose rafters for installation.
You can make rafters with your own hands; you can read how to do this.
For this parameter you need to consider:
Determining the angle of inclination
It is possible for such a calculation proceed from roofing material, which will be used in the future, because each of the materials has its own requirements:
- For The size of the slope angle must be more than 22 degrees. If the angle is smaller, this means water will get into the gaps;
- For this parameter must exceed 14 degrees, otherwise, sheets of material may be torn off like a fan;
- For the angle can be no less than 12 degrees;
- For bitumen shingles this indicator should be no more than 15 degrees. If the angle exceeds this figure, then there is a possibility of the material sliding off the roof during hot weather, because the material is attached to mastic;
- For materials roll type, variations in the angle value can range from 3 to 25 degrees. This indicator depends on the number of layers of material. A larger number of layers allows you to make the slope angle larger.
It is worth understanding that the greater the slope angle, the greater the area of free space under the roof, however, more material is required for such a structure, and, accordingly, more costs.
You can read more about the optimal tilt angle.
Important: minimal permissible value The slope angle is 5 degrees.
The formula for calculating the slope angle is simple and obvious, given that initially there are parameters for the width of the house and the height of the ridge. Having presented a triangle in cross-section, you can substitute data and carry out calculations using Bradis tables or an engineering calculator.
We need to calculate the tangent of an acute angle in a triangle. In this case it will be equal to 34 degrees.
Formula: tg β = Hk / (Lobas/2) = 2/3 = 0.667
Determining the angle of the roof
Calculation of loads on the rafter system
Before proceeding with this section of the calculations, you need to consider all possible loads on the rafters. , which also affects the load. Types of loads:
Types of load:
- Constant. This type of load is constantly felt by the rafters; it is exerted by the roof structure, material, sheathing, films and other small elements of the system. average value this parameter is 40-45 kg/m2.
- Variable. This type of load depends on the climate and the area where the building is located, since it is caused by precipitation in a given region.
- Special. This parameter is relevant if the location of the house is a seismically active zone. But in most cases, additional strength is enough.
Important: best when calculating the strength, make a reserve, for this, 10% is added to the resulting value. It is also worth taking into account the recommendation that 1 m2 should not bear a weight of more than 50 kg.
It is very important to take into account the load exerted by the wind. Indicators of this value can be taken from SNiP in the “Loads and Impacts” section.
- Find out the snow weight parameter. This indicator mainly varies from 80 to 320 kg/m2;
- Multiply by the coefficient that is necessary to take into account wind pressure and aerodynamic properties. This value is indicated in the SNiP table and is applied individually. Source SNiP 2.01.07-85. (V in this example) that will need to be purchased for construction.
- The length of the roof in this example is 10m. To find out this parameter, you need to measure the length of the skate;
- The length of the rafters was calculated and equals 3.6 m (+0.5-0.7 m);
- Based on this, the area of one slope will be equal to 41 m2. General value area – 82 m2, i.e. area of one slope multiplied by 2.
- 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 of attic finishing materials;
- climatic loads (wind, snow accumulation).
To do this, it is necessary to divide the resulting value of the roof area by the area of one sheet of metal tiles.
Important: do not forget about the allowances for the roof canopies of 0.5-0.7 m.
Roofing kit
Conclusion
It is best to check all calculations several times to avoid errors. When this painstaking preparatory process is completed, you can safely begin purchasing the material and prepare it in accordance with the dimensions obtained.
After this, the roof installation process will be simple and quick. And our gable roof calculator will help you with the calculations.
Useful video
Video instructions for using the calculator:
In contact with
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 the “rafter step”.
The strength of the roofing structure, the maximum permissible load per square meter and the materials that can be used for roofing work depend on it.
According to GOSTs, the minimum permissible value of the rafter pitch is 60 cm, the average exceeds 1 m.
To determine the approximate pitch, 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:
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 support points.
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. Maximum permissible length The span of the rafters does not even 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 the pitch, and vice versa.
The slate sheet has a standard length of 175 mm, the sheathing pitch is selected so 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 determine the exact length of the rafter pitch for slate only by taking accurate measurements and calculating the total weight of 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.
Secure the upper support of the rafter system to ridge run instead of the side. 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 material must be used for 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 lathing with minimum cross-section beams 25 mm by 100 mm.
With a rafter pitch of 80 cm, 30 mm per 100 mm, etc. Important role The angle of inclination of the roof also plays a role: when the slope is less than 15 degrees, it is recommended to lay a continuous sheathing under the corrugated sheeting, which is much heavier than sparse sheathing.
Since both are relatively light in weight, supporting structure can be quite light, which reduces 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 more thick timber measuring 40 mm by 50 mm, and keep the rafter pitch to a minimum (60 cm).