The rafter system is the "skeleton" of any roof structure. The reliability, quality and durability of the roof made directly depends on the correctness of its manufacture and installation. If desired, you can handle the arrangement of the truss system yourself. Do you want to know how? Check out the following guide!
There are layered and hanging truss systems. According to statistics, layered structures are most often used. When arranging such a system, they run into the Mauerlat. The function of the central part is performed by a simple ridge run. To increase the strength of the system, supporting beams are mounted.
In the case of hanging rafters, the design of the system is completed with additional racks that contribute to the optimal distribution of the load over the entire area of the roof structure.
We take an additional pair of nails and fix the angle set between the boards. This template is ready. Additionally fix it with a crossbar. To ensure that the set slope angle of the roof slope does not change under the influence of loads, fasten the crossbar with self-tapping screws.
Be extremely careful when creating a template. Even due to the slightest deviations, the entire structure can deteriorate.
Next, we make a new template for preparing mounting cuts on the system elements. Use plywood 0.5 cm thick. Use a 2.5 cm board for reinforcement. Select the dimensions of the cuts taking into account the cross section of the rafters used.
Using ready-made templates, we make cuts and begin to assemble the farm.
Video - Gable roof truss system
Farm assembly order
The design includes supporting legs and connecting components. The farm looks like a triangle. Perform the work in the specified sequence, and the finished structure will be able to adequately transfer all incoming
The farm can be done on the ground with a further rise up or directly on the roof. The first option is simpler and more convenient to implement.
We assemble the truss truss in the following order. First, we cut the prepared material to the desired size, join the bars with the upper edges and fasten them with screws. To prevent the appearance of cracks in the bonding points, we pre-drill holes in the bars with a diameter slightly smaller than the size of the fasteners.
We also use a crossbar to connect the rafter legs. Fixing is carried out half a meter below the upper point of fastening of the elements. Crossbars will increase the rigidity of the structure and eliminate the risk of deflection. We fasten the crossbar in recesses, previously equipped in the rafters by cutting.
If necessary, the rafters are cut at an angle, if this is required by the features of the equipped roof structure.
Roof truss installation
We install roof trusses in the following sequence:
- we mount extreme farms;
- fix the central trusses.
When installing extreme trusses, we adhere to the following important rules:
After completing the installation of the outer trusses, we proceed to fixing the central and subsequent structures, if their placement is provided for by the project. The optimal truss installation step is 100 cm.
To fix the central rafter triangle, we use temporary jibs. After the visor is installed, the jibs can be removed. Recommendations for fastening the central and other trusses are the same as in the case of the outer structures.
After installing all the structural elements, we proceed to fastening the battens and further arrangement of the roofing system: moisture, heat and vapor barrier, as well as installation of the selected finishing coating.
Successful work!
Prices for various types of fasteners for rafters
Fasteners for rafters
Video - Do-it-yourself rafters. shed roof
Video - Hip roof. truss system
For low-rise buildings, a rafter roof is perfect. It will decorate the facade of the house, and with a sufficient slope, snow does not accumulate on such a roof, unlike a flat structure.
One of the types of roof rafters - gable. This is a fairly simple system, which is formed by two slopes. The slope of the roof is the entire inclined plane, with the help of which a drain is provided.
The structure rests on two parallel walls. Such a roof forms two triangular side pediments. A pediment is the end of a building's facade.
Advantages of a gable system
- Ease of Design.
The calculation of the bearing capacity and the necessary materials for the installation of such a roof is quite simple, since there are few options for the types and sizes of supporting structures; - Ease of installation.
A gable roof does not have complex structural elements. A small number of standard sizes allows you to quickly install all the elements of the roof; - Ease of use.
The fewer different breaks the roof has, the more reliably it protects the home. In the simplest version, a gable roof has only one break - a ridge. Such a roof is easier to repair in case of defects; - Free space.
For the arrangement of the attic, a gable roof is preferable, since it “eats up” space less. For comparison, consider a 6x6 m house with an attic. At the outer walls, the height from the floor of the room to the roof is 1.5 m, at the ridge - 3 m. For a gable roof under such conditions, the volume of the room will be 81 cubic meters, and for a hip roof with four slopes, 72 cubic meters. For larger building sizes, volume loss will increase.
Construction types
There are four main types of gable roofs:
- symmetrical.
Reliable, stable, easy to perform, based on an isosceles triangle; - Asymmetrical.
The ridge is not located in the center, the roof slopes have different slopes; - Polyline symmetrical.
Roof slopes are broken. Significantly increases the height of the room; - Polyline asymmetrical.
The attic or attic room is smaller than in the previous case. The roof has a very unusual appearance.
The choice of the type of gable roof depends on the purpose of the room located directly under it and the architectural appearance of the building.
General principles for calculating the truss system
The most important load-bearing parts of the gable roof truss system of a building are the mauerlat, crossbar and rafters. Mauerlat works in compression, so its cross section can be taken conditionally.
The crossbar and rafter legs experience a bending moment.
The calculation of such structures is carried out in terms of strength and stiffness. For small buildings, you can choose their cross section approximately, but for serious buildings, for safety and material saving purposes, the calculation of the truss system should be performed by a professional.
Roof self-weight load
To perform the calculation, you need to know the load per 1 sq.m. roofs.
To do this, you need to add the masses of 1 sq.m. all roofing materials:
- filing(if it is, it is most often performed from drywall);
- rafter legs. To calculate the weight of the rafters per square meter of the roof, you need to find the mass of the running meter of the rafter leg and divide this number by the pitch of the rafters in meters. For the calculation, you can take the approximate cross section of the rafter, the area of \u200b\u200bthis section must be multiplied by the density of the wood;
- heater (if any). The density of the insulation must be indicated by the manufacturer, it must be multiplied by the thickness;
- crate. To ensure a margin, a continuous crate can be taken into account. For example, 1 sq.m. lathing from a board 32 mm thick will weigh approximately 25 kilograms;
- roofing material. Weight 1 sq.m. coatings are usually specified by the manufacturer.
Snow load
The snow load for each area is different and is equal to the weight of the snow cover on a horizontal plane.
On the territory of Russia, it can take values from 80 to 560 kilograms per square meter. On the Internet, you can easily find a snow load distribution map and select the right number based on the construction area.
Roof pitch
The angle of inclination of the roof is quite easy to calculate, knowing the geometry and having an engineering calculator or a standard calculator on a personal computer at hand.
If we divide the height of the roof rise by the distance from the ridge to the cornice in the plan, we get the slope of the roof in fractions or the tangent of the angle of inclination. In order to calculate the angle, it is enough just to find the arc tangent.
If using an engineering calculator is difficult, the arc tangent can be found using an online calculator.
Rafter step calculation
The pitch of the rafters of the attic roof should be chosen for reasons of ease of installation of the insulation. Mats usually have a width of 60 centimeters, so the pitch of the rafters should be chosen so that the distance between them in cleanliness is 58 or 118 centimeters. Two centimeters will allow you to install the insulation boards very tightly, which will allow it to stick between the rafters and improve thermal insulation.
Rafter leg length
Leg length is easy to calculate using the formula:
L/cosα,
here L is the distance from the roof ridge to the inner surface of the outer wall in plan, and cosα is the cosine of the roof pitch angle. With rigid fastening, you need to add the size of the notch.
Section of the rafter leg
The cross section of the rafter leg must be selected as a multiple of the size of the boards and timber.
An example of a simple calculation of the section of the rafter leg:
- we find the load per 1 linear meter of the rafter.
q =(1.1*weight of 1 sq.m. of roof*cosα + 1.4*normative snow load*cosα2)* rafter spacing; - find W.
W= q * 1.25 * flight of rafters / 130; - solve the equation:
W= b*h2/6.
In this equation, b is the width of the section of the rafter leg, and h is the height.
To solve, you need to ask for the width and find the height by solving a simple quadratic equation. The width can be set to 5 cm, 7.5 cm, 10 cm, 15 cm. For small spans, a width of 15 cm is impractical.
To calculate the truss systems, there are all kinds of tables, programs, online calculators.
The main elements of the roof
The main elements of a gable roof, like any other roof truss, are:
Rafter roof with attic
To fully use the space under the roof, you can design an attic.
Attic floor- This is the floor in the attic space. The facade of the attic is completely or partially formed by the roof surfaces. According to regulatory documents, in order for a room to be considered an attic, the line of intersection of the roof plane and the outer wall should not be higher than 1.5 m from the floor level. If this requirement is not met, the space will be considered a normal floor.
The roof of the attic floor differs from the roof of the attic floor by the presence of a heater in its design. Most often, mineral wool boards are used to insulate the attic roof.
Lighting of the attic space can be carried out in three ways:
- window openings in the gables;
- dormers;
- roof windows.
dormer window - this is a window structure that has a frame mounted simultaneously with the truss system. This frame is made of wood. The dormer has its own small roof, which can be gable or cylindrical. The double-glazed window is installed vertically.
roof window- This is a window specially designed for use on a rafter roof. It is installed in the plane of the slope in an inclined position. The roof window must withstand the calculated snow load. It is better not to use this type of windows in roofs with a slight slope.
The choice of roofing material
After the appearance of the roof is determined, you can proceed to the choice of material. There are several types of modern coatings. In the list below, material options are listed in descending order of average market value.
- Ceramic tiles.
Ceramics as a roofing material has a long history. The ceramic roof is reliable and durable. The disadvantages of this material are the price and the large mass. Under the roof of ceramic tiles, you will have to arrange a reinforced truss system and crate; - Cement-sand tiles.
It has almost all the characteristics of ceramic, but costs a little less; - Flexible shingles.
It has good soundproofing characteristics. Thanks to the rough surface, the tiles are able to prevent snow from moving off the roof. Requires a continuous crate, usually a layer of moisture-resistant plywood is used. Cannot be used on roofs with large slopes; - Metal tile.
Compared to previous coatings, it is lighter in weight. Easy to mount. The disadvantage of a metal roof is that it can be too noisy when it rains. - seam roof.
The most attractive option in terms of cost. It requires special qualifications during installation, since it will be difficult for a non-professional to make high-quality connections. Installation is more laborious than that of metal and flexible tiles. The same "noisy" as metal tiles.
The material of the roof depends entirely on the desires and capabilities of the customer. The exception is roofs with too much or too little slope, since all materials have limits on the slope of the slope.
Types of truss systems
Structural roof truss systems can be of three types:
- Rafters.
The rafters rest on two sides. From below - on the Mauerlat, from above - on the crossbar. Racks and struts can be used as intermediate supports. Most often used in buildings with a small distance between the ends or, if possible, put racks or a wall in the middle of the attic.
With large spans of rafters (large distances between the longitudinal walls), racks, struts or puffs can be additionally used.
Laminated rafters are easy to calculate.
Usually the most powerful element of such a system is the crossbar, which bears half the load of the entire roof structure. - Hanging rafters.
In the absence of the possibility of using a crossbar as an upper support, it is reasonable to use this truss system.
Hanging rafters rest only on the Mauerlat, and at the top point they are interconnected with the help of an overlay.
This truss system works like a truss under load. The greatest pressure falls on the outer walls. There is a horizontal force - thrust, which can lead to displacement of the walls. In the design of hanging rafters, the expansion force is perceived by a puff, which tightens the rafter legs and prevents them from moving apart.
Hanging rafters are classified depending on the location of the puff:
1) Triangular three-hinged arch.
The puff and rafters form a triangle. The puff is located at the level of the overlap;
2) Triangular three-hinged arch with suspension.
With a large span of rafters, the tightening may not pass according to the deflection requirements. To prevent it from sagging, the puff is suspended from the ridge. But with such a system, as well as with a system of layered rafters, a row of racks is formed in the middle of the attic;
3) Triangular three-hinged arch with a raised puff.
The puff is most often located at the level of the ceiling of the attic room. Such a scheme is less beneficial from the point of view of the design. The higher the puff is located, the greater the thrust it perceives.
Hanging rafters must be considered as a triangular truss, which complicates the calculation. - Combined rafters.
The combined system includes spacer layered rafters. They need both bolt installation and tightening. Unlike the previous options, in which the rafters are hinged to the Mauerlat, here the rafter leg is rigidly attached, so there is a thrust in the system. For such a system, the Mauerlat must be securely attached to the wall, and the wall itself must be strong and thick. An excellent option would be to run a reinforced concrete belt around the perimeter.
Installation of the truss system
Installation takes place in the following order:
- mauerlat laying;
- installation of a crossbar (if any);
- layout of rafters;
- insulation (if any);
- crate;
- roofing material.
Attaching the rafter leg to the Mauerlat can be rigid and articulated.
Hinged fastening
It makes it possible to compensate for the expansion of wood under the influence of humidity and temperature changes.
Fastening can be done in several ways:
- using special fasteners, a metal "sled";
- using a mounting plate;
- washed down on the rafter leg. The junction of the rafter leg and the Mauerlat is fixed with nails.
Rigid fastening
The rafter is attached to the Mauerlat with a notch and securely fixed with nails hammered at an angle with respect to each other. One nail is driven vertically into the surface of the Mauerlat. Such a connection excludes displacement in any plane.
The gable truss system has undeniable advantages. You can design and install it yourself, you just need to take this issue responsibly and think through everything to the smallest detail.
Online calculator produces exact calculation of rafters online(calculates the dimensions of the rafters for the roof: the length of the rafters, the length of the overhang, the angle of the cut, the distance to the gash). Drawings and dimensions of rafters are generated in real time.
The calculator provides an online calculation of the length of the rafters gable roof. Calculate the rafters of a shed roof with another calculator.
In the "Specify dimensions" block, you must enter the roof data, after selecting the units of measurement that suit you. The image clearly shows all the necessary parameters.
The dimensions required for calculating the rafters:
- roof height- the distance from the level of the "floor" of the attic to the ridge of the roof.
- roof width- the distance between the support points of the rafters. Usually this is the edge of the Mauerlat on the outside of the wall.
- Eaves is the distance from the edge of the wall to the edge of the roof.
- Rafter Width- the width of the rafter board (usually 10 - 15 cm).
- Rafter thickness- thickness of the rafter board (usually 5 cm)
- Washed down depth- the distance from the edge of the board to the extreme point of the gash (you can not do more than 1/3 of the width of the rafter board)
The distance from the edge of the rafter board to the cut should be marked only at the angle of the cut, which the rafter calculation calculator gives you.
The calculated dimensions of the rafters may differ slightly during construction due to the presence of errors at the construction site. Please consider this nuance and before making the whole truss system, make one rafter, which you will use later as a template.
On the tab " 3D viewing"A three-dimensional model of the finished rafter is presented, which can be viewed from all sides: rotate, move, zoom in, reduce. To move the rafter model, first place the cursor on the model, hold down the right mouse button, then move. The rafter model is rotated by holding the left mouse button. To move the rafter model, zoom in/out scroll the mouse wheel.
The thickness of the rafter is determined from the loads on the rafter system, from the step between the rafters, from the length of the rafter, etc. To determine the thickness of the rafters, use the useful article on our website Correct calculation of the truss system.
The gable roof rafter calculator will help to greatly simplify independent calculations, determine the main required dimensions, as well as the amount of material required for the construction of gable roof rafters.
Use the online gable roof calculator to calculate the amount of lathing, the angle of inclination of the truss system, the load (wind and snow) on the roof. Our free calculator will help you calculate the required amount of material for a given type of roof.
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) Bituminous (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 board (5 kg/m2) Keramoplast (5.5 kg/m2) Seam roof (6 kg/m2) Polymer-sand tile (25 kg/m2) Ondulin (Euro slate) (4 kg/m2) Composite tile (7 kg/m2) ) Natural slate (40 kg/m2) Specify the weight of 1 square meter of coating (? kg/m2)
kg/m2
Enter roof parameters:
Base Width A (cm)
Base length D (cm)
Lift height B (cm)
Length of side overhangs C (cm)
Front and rear overhang length E (cm)
Rafter:
Rafter pitch (cm)
Type of wood for rafters (cm)
Working section of the side rafter (optional) (cm)
Lathing calculation:
Purlin board width (cm)
Lathing board thickness (cm)
Distance between decking boards
F(cm)
Snow load calculation:
Select your region using the map below
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 building ridge
5 m from 5 m to 10 m from 10 m
Terrain type
Open area Closed area Urban areas
Calculation results
Roof pitch: 0 degrees.
The angle of inclination is suitable for this material.
The angle of inclination for this material is desirable to increase!
It is desirable to reduce the angle of inclination for this material!
Roof surface area: 0 m2.
Approximate weight of roofing material: 0 kg.
Number of rolls of insulation material with 10% overlap (1×15 m): 0 rolls.
Rafter:
Load on the truss system: 0 kg/m2.
Rafter length: 0 cm
Number of rafters: 0 pcs
Lathing:
Number of rows of lathing (for the entire roof): 0 rows.
Uniform distance between the boards of the crate: 0 cm
The number of boards of the crate with a standard length of 6 meters: 0 pcs
Volume of boards of an obreshetka: 0 m 3 .
Approximate weight of the boards of the crate: 0 kg.
About the calculator
The online calculator for a gable roof, also called a gable roof, will help you calculate the desired angle of inclination of the slopes, determine the cross section and number of rafters, the amount of materials per sheathing, the consumption of insulating materials, and at the same time take into account existing standards for wind and snow loads. You do not have to perform unnecessary additional calculations, because this calculator contains most of the existing roofing materials. You can easily calculate the consumption and weight of such common materials as bituminous tiles, cement-sand and ceramic tiles, metal tiles, bituminous and asbestos-cement slate, ondulin and others. If you are using a non-standard material, or want to get more accurate calculations, you can specify the weight of your own roofing material by selecting the appropriate item in the drop-down list of materials.
Note!
The calculator makes calculations in accordance with the current SNiP "Loads and Impacts" and TCP 45-5.05-146-2009.
A gable roof (there are variants of the name "gable roof" and "gable roof") - the most common type of roof, in which there are two inclined slopes from the ridge to the outer walls of the structure. The popularity of this type of roofs is explained by their moderate cost, ease of construction, good performance and attractive appearance.
In this design, the rafters of different slopes lean against each other in pairs and are sheathed with sheathing boards. The end of a building with a gable roof has a triangular shape and is called a pediment (the name “tongue” is also found). Usually, under the slopes of the roof there is an attic space, naturally lit by small window openings located at the top of the gables.
When filling in the fields of the calculator, you can find additional information located under the sign.
For any questions or ideas regarding this calculator, you can write to us using the form at the bottom of the page. We will be glad to hear your opinion.
Additional information about the calculation results
Roof slope
At this angle, the slope and rafters are inclined to the base of the roof. Roofing materials have individual limiting roof slope angles, so for some materials the angle may be outside the permissible limits. Whether your angle satisfies the selected material or not - you will find out in the calculation results. In any case, it is always possible to adjust the height of the roof (B) or the width of the base (A), or choose a different roofing material.
Roof surface area
The area of the entire roof surface, including overhangs. To determine the area of one slope, it is enough to divide the resulting value by two.
Approximate weight of roofing material
The weight of the selected roofing material based on the total roof area (including overhangs).
Number of rolls of insulating material
The amount of insulation material required to build a roof. The quantity indicated in rolls is required for the entire roof area. The standard roll is taken as a basis - 15 meters long, 1 meter wide. The calculation also takes into account an overlap of 10% at the joints.
Load on the truss system
The maximum weight per rafter system. Wind and snow loads, the angle of inclination of the roof, as well as the weight of the entire structure are taken into account.
Rafter length
The full length of the rafters from the roof ridge to the edge of the slope.
Number of rafters
The total number of rafters required for a rafter system at a given pitch.
Minimum cross-section of rafters / Weight of rafters / Timber volume
- The first column shows the sections of the rafters according to GOST 24454-80 Softwood lumber. Here are the sections that can be used in the construction of a given structure. The calculator proceeds from the total loads that can affect the structure of a given roof and selects the cross-sections that satisfy them.
- The second column shows the total weight of all rafters with the specified section, if they are used to build a given roof.
- The third column shows the total volume of this timber in cubic meters. This amount will be useful to you when calculating the cost.
Number of rows of battens
The number of rows of lathing that will be needed for the entire roof with the given parameters. To calculate the number of rows of crates of one slope, you need to divide the resulting value by two.
Uniform spacing between boards
The volume of boards of the crate
The total volume of the crate for a given roof. This value will help you calculate the cost of lumber.
The roof of the house is a load-bearing structure that takes on all the external load (the weight of the roofing pie, its own weight, the weight of the snow cover, etc.) and transfers it to all the load-bearing walls of the house or to internal supports.
In addition to its aesthetic and load-bearing functions, the roof is an enclosing structure, separating the attic from the external environment.
The basis of the roof of any house is the truss system.
This is the frame to which the roof is attached.
It is this skeleton that takes all the loads.
The rafter system consists of:
- rafter legs;
- Mauerlat;
- side runs and ridge run;
- braces, diagonal ties, braces.
When all these elements (except for the Mauerlat) are interconnected, a truss truss is obtained.
The basis of such a farm is a triangle, which is the most rigid of the geometric shapes.
The main element of the roof frame are the rafters.
Rafter calculation
Before you directly start calculating the rafters, you should find out what loads will affect the roof of the house.
That is, on rafter legs.
The loads acting on the roof frame are usually divided into constant and variable.
Constants are those loads that act constantly, regardless of the time of day, season, etc.
This is the weight of the entire roofing pie, the weight of additional equipment that can be installed on the roof (fencing, snow guards, aerators, antennas, etc.).
Variable loads appear at certain times of the year.
For example, snow.
When snow falls on the roof, this is a very decent weight.
In any case, it should be taken into account.
The same with the wind.
It is not always there, but when a strong wind blows, a fairly large wind force acts on the roof frame.
And an inexperienced person is unlikely to succeed.
Although it's worth a try.
Just when calculating, you need to remember a large number of different factors that affect the roof.
At least the weight of the truss system itself with all the elements and fasteners.
Therefore, professionals use special computer programs and calculators to calculate rafters.
How to find out the load on the rafter legs?
The collection of loads should begin with determining the weight of the roofing cake.
If you know what materials will be used and the area of \u200b\u200bthe slopes, then it is not difficult to calculate everything.
It is customary to calculate how much 1 square meter of roof weighs.
And then multiply by the number of squares.
For example, let's calculate the weight of a roofing pie.
The roofing material is ondulin:
- Ondulin. A square meter of ondulin has a weight of 3 kg.
- Waterproofing. If polymer-bitumen insulation is used, then it weighs 5 kg / square meter.
- Insulation. The weight of one square of basalt wool is 10 kg.
- Crate. Boards 2.5 cm thick. Weight per square meter 15 kg.
We summarize all weights: 3+5+10+15= 33 kg.
Then the value obtained as a result of the calculations should be multiplied by a factor of 1.1.
This is a correction factor.
It turns out 34.1 kg.
How much does 1 sq. meter of our roofing cake.
And if the total area of our roof is 100 squares, then it will weigh 341 kg.
Snow load calculationThere is a map of snow loads.
It shows the amount of snow cover in each region.
We calculate the snow load using the following formula: S = Sg x µ.
Sg is the mass of snow cover.
µ is a correction factor.
And this coefficient depends on the angle of inclination of the slopes of your roof.
The larger this angle, the smaller the value of this coefficient.
At angles of inclination greater than 60 degrees, it is not used at all.
Since snow does not collect on the roof.
Calculate wind load
Just as the whole country is divided into regions according to the mass of snow, so it is also divided according to the strength of the winds.
And there is also a special map on which the strength of the wind is indicated in each area.
The following formula is used to calculate wind loads:
Wo - an indicator taken from the map.
k is a correction factor depending on the type of terrain where the building is located and its height.
We calculate the cross section of the rafter leg
The cross section of the rafters depends on three factors:
- from the length of the rafter;
- from the distance between the railings;
- from the loads acting on the roof.
Knowing these parameters, it is easy to determine from the table.
How to calculate the length of the rafter legs of a shed roof
Of all the types of roofs, pitched roofs are the simplest.
There are no complex elements in it at all.
And its installation is carried out on load-bearing walls, which have different heights.
Such a roof is arranged on garages, baths, utility rooms.
To calculate what will be the length of the rafters of a shed roof, you should determine the angle of inclination.
And the angle of inclination of the slope depends, first of all, on the type of roofing material that you want to use.
In the case when it is corrugated board, then the optimal angle of inclination is 20 degrees.
But it is forbidden to make an angle less than 8 degrees!
Otherwise, in the cold season, under the weight of the snow cover, the roof will not withstand and simply fail.
If you will lay metal tiles, then the minimum angle of inclination increases to 25 degrees.
When using slate - 35 degrees.
If the roof is folded, then the angle of inclination can be different: 18 - 35 degrees.
After you figured out the angle of the slope, you need to raise the back wall to such a height that you get the desired angle.
The most difficult thing in such calculations is to find the sine and tangent.
But for this they use this sign:
| Roof slope angle, degrees | Tangent tgA | sine sinA |
|---|---|---|
| 5 | 0,09 | 0,09 |
| 10 | 0,18 | 0,17 |
| 15 | 0,27 | 0,26 |
| 20 | 0,36 | 0,34 |
| 25 | 0,47 | 0,42 |
| 30 | 0,58 | 0,5 |
| 35 | 0,7 | 0,57 |
| 40 | 0,84 | 0,64 |
| 45 | 1,0 | 0,71 |
| 50 | 1,19 | 0,77 |
| 55 | 1,43 | 0,82 |
| 60 | 1,73 | 0,87 |
For example, let's find the length of the rafter and the height of the elevation of the facade wall for a house 5 meters long.
The tilt angle is 25 degrees.
To determine the height of the front wall rise Lbc x tg 25 = 5 x 0.47 = 2.35 meters.
Accordingly, the length of the rafter leg Lc = 2.35 x 0.42 = 5.6 meters.
And do not forget to add the length of the front and rear overhangs to the resulting length, which are necessary in order to provide the walls of the building with protection from slanting rain.
On average, the length of one overhang is 0.5 meters.
If required, this length can be longer.
But less than 0.5 meters is impossible.
This means that 1 meter should be added to the length of the rafter: Lc \u003d 5.6 + 1 \u003d 6.6 meters.
Calculation for a gable roof
The truss system of a gable roof is much more complicated than the truss system of a shed roof.
There are more elements, and the principle of its operation is somewhat different.
To calculate the length of the rafter leg, we use the Pythagorean theorem. 
If you look at the right triangle shown in the figure, you can see that the hypotenuse b is our rafter.
And its length is equal to the length of the leg, divided by the cosine of a specific slope angle.
For example, if the width of the house is 8 meters, and the slope of the slopes is 35 degrees, then the rafter leg will have a length of:
b \u003d 8 / 2 / cos 35 \u003d 8 / 2 / 0.819 \u003d 4.88 meters.
Now it remains to add the length of the visor, about 0.5 meters, to get the desired length of the rafters.
It should be said that these are simplified versions of the calculations of rafters.
In order to get the most accurate data, it is best to use special programs.
For example, the free Arkon program.
The built-in calculator, according to the parameters you set, will automatically calculate both the cross section of the rafter leg and the length of the rafter.
Video about the rafter calculation program.
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