Program for constructing a rafter system. Calculation of rafter system excel. Roof design and calculation of the rafter system in the Arkon program. We calculate the pitch and number of rafter legs
In this article we'll talk about the simple program "Rafters". It is intended for calculating a two-span wooden beam. The software will provide data on the maximum moment, deflection and load-bearing capacity. Let's take a closer look at the representative.
"Rafters" does not require installation, you just need to run the file from the archive. All functionality is in one window. You will need to enter required parameters about spans, inclination angles, height and width in lines and press the button "Calculation", so that the calculation results are displayed below. Please note that there are three types of wood and two calculation modes, this helps to determine the most accurate parameters.
Advantages
- The program is distributed free of charge;
- Does not require installation;
- Russian language is available;
- Simple interface.
Flaws
- Minimal functionality.
"Rafters" provides minimum set tools needed to calculate the roof. However, it fully copes with its task and provides accurate information about the parameters of a two-span beam. The software is easy to use and does not require special skills.
Rate the program:
You need to enable JavaScript to voteRafter system. Calculation of rafters and floor beams. Before starting to build a roof, it is of course desirable that its rafter system be designed for strength. Immediately after the publication of the last article, “Gable roof of a house with your own hands,” I began to receive questions in the mail regarding the choice of the cross-section of rafters and floor beams. Yes, understanding this issue in the vastness of our beloved Internet is indeed quite difficult. There is a lot of information on this topic, but as always it is so scattered and sometimes even contradictory that an inexperienced person, who in his life may not even have encountered such a subject as “Sopromat” (lucky someone), can easily get confused in these wilds. I, in turn, will now try to compose step-by-step algorithm, which will help you independently calculate the rafter system of your future roof and finally get rid of constant doubts - what if it doesn’t hold up, or what if it falls apart. I will say right away that I will not delve into the terms and various formulas. Well, why? There are so many useful and interesting things in the world that you can fill your head with. We just need to build a roof and forget about it. The entire calculation will be described using an example. gable roof, which I wrote about in the previous article. So, Step No. 1: Determine the snow load on the roof. For this we need a map snow loads RF. To enlarge the picture, click on it with the mouse. Below I will provide a link where you can download it to your computer. Using this map, we determine the number of the snow region in which we are building a house and from the table below we select the snow load corresponding to this region (S, kg/m²): If your city is located on the border of the regions, choose a higher load value. There is no need to adjust the resulting figure depending on the angle of inclination of the slopes of our roof. The program we will use will do this itself. Let's say in our example we are building a house in the Moscow region. Moscow is located in the 3rd snow region. The load for it is 180 kg/m². Step #2: Determine the wind load on the roof. For this we need a map of wind loads in the Russian Federation. It can also be downloaded from the link below. Using this map, we also select the corresponding region number and determine the wind load value for it (the values are shown in the lower left corner): Next, the resulting figure must be multiplied by the correction factor “k”, which in turn is determined from the table: Here column A is open coasts seas, lakes and reservoirs, deserts, steppes, forest-steppes and tundras; Column B - urban areas, forests and other areas evenly covered with obstacles. It should be taken into account that in some cases the type of terrain may differ in different directions (for example, a house is located on the outskirts of a populated area). Then select the values from column “A”. Let's return to our example again. Moscow is located in I-th wind region. The height of our house is 6.5 meters. Let's assume that it is being built in a populated area. Thus, we accept the value of the correction factor k=0.65. That is, the wind load in this case will be equal to: 32x0.65=21 kg/m². Step No. 3: You need to download to your computer a calculation program made in the form of an Excel table. We will continue to work in it. Here is the download link: “Calculation rafter system". Also here are maps of snow and wind loads in the Russian Federation. So, download and unpack the archive. We open the file “Calculation of the rafter system”, and we get into the first window - “Loads”: Here we need to change some values in the filled cells blue. All calculations are done automatically. Let's continue to look at our example: - in the “Initial data” plate we change the angle of inclination to 36° (whatever angle you have, write that, well, I think this is clear to everyone); - change the pitch of the rafters to the one we chose. In our case it is 0.6 meters; - Load roof (self-weight load roofing material) - we select this value from the table: For our example, we select metal tiles with a weight of 5 kg/m². - Snow. region - here we enter the sum of the values of snow and wind loads that we received earlier, i.e. 180+21=201 kg/m²; - Insulation (mans.) - we leave this value unchanged if we lay insulation between the rafters. If we do cold attic without insulation - change the value to 0; - enter into the “Lathing” sign required dimensions sheathings. In our case, for metal tiles, we will change the pitch of the sheathing by 0.35 m and the width by 10 cm. We leave the height unchanged. All other loads (from the own weight of the rafters and sheathing) are taken into account by the program automatically. Now let’s see what we got: We see the inscription “The load-bearing capacity of the sheathing is ensured!” We don’t touch anything else in this window; we don’t even need to understand what the numbers are in other cells. If, for example, we choose a different rafter pitch (more), it may turn out that load bearing capacity sheathing will not be provided. Then you will need to select other dimensions of the sheathing, for example, increase its width, etc. In general, I think you will figure it out. Step No. 4: Click at the bottom of the working screen on the “Sling 1” tab and go to the window for calculating rafters with two support points. Here, all the input data we previously entered is already entered by the program automatically (this will be the case in all other windows). In our example from the article “Do-it-yourself gable roof of a house,” the rafters have three support points. But let's imagine that there are no intermediate posts and let's make a calculation: - change the length of its horizontal projection on the rafter diagram (the cell is filled in blue). In our example, it is 4.4 meters. - in the “Calculation of rafters” plate we change the value of rafter thickness B (specified) to the one we selected. We set 5 cm. This value must be greater than that indicated in the Vtr (sustainable) cell; - now in the line “Accept N” we need to enter the selected width of the rafters in centimeters. It must be greater than the values indicated in the lines “Ntr., (strength)” and “Ntr., (deflection)”. If this condition is met, all the inscriptions at the bottom under the rafter diagram will look like “Condition met.” The line “N, (by grade)” indicates the value that the program itself asks us to choose. We can take this number, or we can take another. We usually choose sections available in the store. So, what we got is shown in the figure: In our example, in order to meet all the strength conditions, it is necessary to choose rafters with a section of 5x20 cm. But the roof diagram I showed in the last article has rafters with three support points. Therefore, to calculate it, we move on to the next step. Step No. 5: Click at the bottom of the working screen on the “Sling.2” or “Sling. 3″. This opens a window for calculating rafters with 3 support points. We select the tab we need depending on the location of the middle support (rack). If it is located to the right of the middle of the rafter, i.e. L/L1<2, то пользуемся вкладкой «Строп.2″. Если стойка расположена левее середины стропила, т. е. L/L1>2, then use the “Sling 3” tab. If the stand is exactly in the middle, you can use any tab, the results will be the same. - on the rafter diagram, we transfer the dimensions in cells filled with blue (except for Ru); - using the same principle as described above, we select the cross-sectional dimensions of the rafters. For our example, I took the dimensions 5x15 cm. Although 5x10 cm was also possible. I’m just used to working with such boards, and there will be a larger margin of safety. Now it is important: from the drawing obtained during the calculation, we will need to write down the value of the vertical load acting on the post (in our example (see figure above) it is equal to 343.40 kg) and the bending moment acting on the post (Mop. = 78.57 kghm). We will need these numbers later when calculating the racks and floor beams. Next, if you go to the “Arch” tab, a window will open for calculating the rafter system, which is a ridge arch (two rafters and a tie). I won’t consider it; it’s not suitable for our roof. We have too large a span between the supports and a small angle of inclination of the slopes. There you will get rafters with a cross section of about 10x25 cm, which is of course unacceptable for us. For smaller spans such a scheme can be used. I am sure that those who understand what I wrote above will understand this calculation themselves. If you still have questions, write in the comments. And we move on to the next step. Step #6: Go to the “Rack” tab. Well, everything is simple here. - we enter the previously determined values of the vertical load on the stand and the bending moment in the figure in the cells “N=” and “M=”, respectively. We recorded them in kilograms, we enter them in tons, and the values are automatically rounded; - also in the figure we change the height of the rack (in our example it is 167 cm) and set the dimensions of the section we have chosen. I chose a 5x15 cm board. At the bottom in the center we see the inscription “Central secured!” and “Off-center.” secured." So everything is fine. The safety factors "Kz" are very large, so you can safely reduce the cross-section of the racks. But we will leave it as it is. The result of the calculation is in the figure: Step No. 7: Go to the “Beam” tab. Floor beams are subject to both distributed and concentrated loads. We need to take both into account. In our example, beams of the same section overlap spans different widths. We, of course, make calculations for a wider span: - in the “Distributed Load” plate we indicate the pitch and span of the beams (we take 0.6 m and 4 m from the example, respectively); - we take the values Load (normal) = 350 kg/m² and Load (calc.) = 450 kg/m². The values of these loads in accordance with SNiP are averaged and taken with a good margin of safety. They include the load from the dead weight of the floors and the operational load (furniture, people, etc.); - in the line “B, given” we enter the section width of the beams we have chosen (in our example it is 10 cm); - in the lines “H, strength” and “H, deflection” the minimum possible heights of the cross-section of the beams will be indicated at which it will not break and its deflection will be acceptable. We are interested in the larger of these numbers. We take the height of the beam section based on it. In our example, a beam with a cross-section of 10x20 cm is suitable: So, if we did not have racks resting on the floor beams, the calculation would be completed at this point. But in our example there are racks. They create a concentrated load, so we continue to fill out the “Concentrated load” and “Distributed + concentrated” plates: - in both plates we enter the dimensions of our spans (here I think everything is clear); - in the “Concentrated load” plate we change the values of Load (normal) and Load (calculated) to the figure that we received above when calculating rafters with three points of support - this is the vertical load on the rack (in our example 343.40 kg) ; - in both plates we enter the accepted width of the beam section (10 cm); - the height of the beam section is determined according to the “Distribution + Focus” plate. Again we focus on a larger value. For our roof we take 20 cm (see figure above). This completes the calculation of the rafter system. I almost forgot to say: the calculation program we use is applicable for rafter systems made of pine (except Weymouth), spruce, European and Japanese larch. All wood used is 2nd grade. If you use other wood, some changes will need to be made to the program. Since other types of wood are rarely used in our country, I will not describe now what needs to be changed. Read more.
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Can you imagine a person without bones? In the same way, a pitched roof without a rafter system is more like a structure from a fairy tale about the three little pigs, which can easily be swept away by natural elements. Strong and reliable system rafters are the key to the durability of the roof structure. In order to design a high-quality rafter system, it is necessary to take into account and predict the main factors affecting the strength of the structure.
Take into account all roof bends, correction factors for uneven distribution snow on the surface, snow drift by the wind, the slope of the slopes, all aerodynamic coefficients, forces of influence on the structural elements of the roof and so on - calculating all this as close as possible to the real situation, as well as taking into account all the loads and skillfully assembling their combinations is not an easy task.
If you want to understand it thoroughly, a list of useful literature is given at the end of the article. Of course, a strength of strength course for a complete understanding of the principles and impeccable calculation of the rafter system cannot be fit into one article, so we will present the main points for simplified versioncalculation.
Load classification
Loads on the rafter system are classified into:
1) Basic:
- permanent loads: the weight of the rafters and roof themselves,
- long-term loads- snow and temperature loads with a reduced design value (used when it is necessary to take into account the influence of load duration when testing endurance),
- variable short-term influence- snow and temperature effect at full calculated value.
2) Additional- wind pressure, weight of builders, ice loads.
3) Force majeure- explosions, seismic activity, fire, accidents.
To carry out the calculation of the rafter system, it is customary to calculate the maximum loads in order to then, based on the calculated values, determine the parameters of the elements of the rafter system that can withstand these loads.
Calculation of the rafter system pitched roofs produced according to two limit states:
a) The limit at which structural failure occurs. The maximum possible loads on the structural strength of the rafters should be less than the maximum permissible.
b) Limit state at which deflections and deformations occur. The resulting deflection of the system under load should be less than the maximum possible.
For more simple calculation Only the first method applies.
Calculation of snow loads on the roof
To count snow load use the following formula: Ms = Q x Ks x Kc
Q- weight of snow cover covering 1 m2 of flat horizontal surface roofs. Depends on the territory and is determined by the map in Figure No. X for the second limit state- calculation of deflection (when the house is located at the junction of two zones, a snow load with a large value is selected).
For strength calculations according to the first type, the load value is selected according to the area of residence on the map (the first digit in the indicated fraction is the numerator), or is taken from table No. 1:
The first value in the table is measured in kPa, in parentheses the desired converted value is in kg/m2.
Ks- correction factor for the roof slope angle.
- For roofs with steep slopes with an angle of more than 60 degrees, snow loads are not taken into account, Ks=0 (snow does not accumulate on steeply pitched roofs).
- For roofs with an angle from 25 to 60, the coefficient is 0.7.
- For others it is equal to 1.
The angle of the roof can be determined online roof calculator the appropriate type.
Kc- coefficient of wind removal of snow from roofs. Assuming a flat roof with a slope angle of 7-12 degrees in areas on the map with a wind speed of 4 m/s, Kc is taken = 0.85. The map shows zoning based on wind speed.
Drift factor Kc is not taken into account in areas with January temperatures warmer than -5 degrees, since an ice crust forms on the roof and snow does not blow off. The coefficient is not taken into account if the building is blocked from the wind by a taller neighboring building.
The snow falls unevenly. Often on the leeward side a so-called snow bag, especially at joints and kinks (valley). Therefore, if you want strong roof, keep the pitch of the rafters to a minimum in this place, and also pay close attention to the recommendations of the roofing material manufacturers - snow can break off the overhang if it is of the wrong size.
We remind you that the calculation given above is presented to your attention in a simplified form. For a more reliable calculation, we recommend multiplying the result by the load safety factor (for snow load = 1.4).
Calculation of wind loads on the rafter system
We've sorted out the snow pressure, now let's move on to calculating the wind influence.
Regardless of the angle of the slope, the wind has a strong impact on the roof: it tries to throw off a steeply pitched roof, more flat roof- lift from the leeward side.
To calculate the wind load, its horizontal direction is taken into account, while it blows bidirectionally: on the facade and on the roof slope. In the first case, the flow is divided into several - part goes down to the foundation, part of the flow tangentially from below vertically presses on the roof overhang, trying to lift it.
In the second case, acting on the roof slopes, the wind presses perpendicular to the slope, pressing it in; a vortex is also formed tangentially on the windward side, going around the ridge and turning into a lifting force on the leeward side, due to the difference in wind pressure on both sides.
To calculate the average wind load use the formula
Mv = Wo x Kv x Kc x strength factor,
Where Wo- wind pressure load determined from the map
Kv- wind pressure correction factor, depending on the height of the building and the terrain.
Kc- aerodynamic coefficient, depends on the geometry of the roof structure and wind direction. Values are negative for the leeward side, positive for the windward side
For pitched roof it is necessary to take the coefficient from the table for Ce1.
To simplify the calculation, it is easier to take the maximum value of C, equal to 0.8.
Calculation of own weight, roofing pie
To calculate permanent load you need to calculate the weight of the roof (roofing pie - see Figure X below) per 1 m2, the resulting weight must be multiplied by a correction factor of 1.1 - the rafter system must withstand this load throughout its entire service life.
The weight of the roof consists of:
- the volume of wood (m3) used as sheathing is multiplied by the density of the wood (500 kg/m3)
- rafter system weight
- weight of 1m2 roofing material
- weight 1m2 of insulation weight
- weight of 1m2 of finishing material
- weight 1m2 of waterproofing.
All these parameters can be easily obtained by checking this data with the seller, or looking at the main characteristics on the label: m3, m2, density, thickness - perform simple arithmetic operations.
Example: for insulation with a density of 35 kg/m3, packed in a roll 10 cm or 0.1 m thick, 10 m long and 1.2 m wide, weight 1 m2 will be equal to (0.1 x 1.2 x 10) x 35 / (0.1 x 1.2) = 3.5 kg/m2. The weight of other materials can be calculated using the same principle, just do not forget to convert centimeters to meters.
More often the roof load per 1 m2 does not exceed 50 kg, therefore, when making calculations, this value is used, multiplied by 1.1, i.e. use 55 kg/m2, which itself is taken as a reserve.
More data can be taken from the table below:
10 - 15 kg/m² |
|
Ceramic tiles | 35 - 50kg/m² |
Cement-sand tiles | 40 - 50 kg/m² |
Bituminous shingles | 8 - 12 kg/m² |
Metal tiles | |
Corrugated sheet | |
Subfloor weight | 18 - 20 kg/m² |
Sheathing weight | 8 - 12 kg/m² |
Rafter system weight | 15 - 20 kg/m² |
Collecting loads
According to the simplified version, now it is necessary to add up all the loads found above by simple summation, we will get the final load in kilograms per 1 m2 of roof.
Calculation of the rafter system
After collecting the main loads, you can already determine the main parameters of the rafters.
falls on each rafter leg separately, convert kg/m2 to kg/m.We calculate using the formula: N = rafter spacing x Q, Where
N - uniform load on the rafter leg, kg/m
rafter pitch - distance between rafters, m
Q - final roof load calculated above, kg/m²
It is clear from the formula that by changing the distance between the rafters, you can regulate the uniform load on each rafter leg. Typically, the pitch of the rafters is in the range from 0.6 to 1.2 m. For a roof with insulation, when choosing a pitch, it is reasonable to focus on the parameters of the insulation sheet.
In general, when determining the installation pitch of the rafters, it is better to proceed from economic considerations: calculate all the options for the location of the rafters and choose the cheapest and optimal in terms of quantitative consumption of materials for truss structure.
- Calculation of the cross-section and thickness of the rafter leg
In the construction of private houses and cottages, when choosing the section and thickness of the rafters, they are guided by the table below (the cross section of the rafters is indicated in mm). The table contains average values for the territory of Russia, and also takes into account the sizes building materials presented on the market. IN general case, this table is enough to determine what cross-section of timber you need to purchase.
However, we should not forget that the dimensions of the rafter leg depend on the design of the rafter system, the quality of the material used, constant and variable loads exerted on the roof.
In practice, when building a private residential building, boards with a cross section of 50x150 mm (thickness x width) are most often used for rafters.
Independent calculation of rafter cross-section
As mentioned above, rafters are calculated based on maximum load and deflection. In the first case, the maximum bending moment is taken into account, in the second, the section of the rafter leg is checked for resistance to deflection over the longest section of the span. The formulas are quite complex, so we have chosen for you simplified version.
The section thickness (or height) is calculated using the formula:
a) If the roof angle< 30°, стропила рассматриваются как изгибаемые
H ≥ 8.6 x Lm x √(N / (B x Rben))
b) If the roof slope is > 30°, the rafters are flexural and compressive
H ≥ 9.5 x Lm x √(N / (B x Rben))
Designations:
H, cm- rafter height
Lm, m- working section of the longest rafter leg
N,
kg/m- distributed load on the rafter leg
B, cm- rafter width
Rizg, kg/cm²- bending resistance of wood
For pine and spruce Rizg depending on the type of wood is equal to:
It is important to check whether the deflection exceeds the permitted value.
The deflection of the rafters should be less L/200- length of the thing being checked longest span between supports in centimeters divided by 200.
This condition is true if the following inequality is satisfied:
3,125 xNx(Lm)³ / (BxH³) ≤ 1
N (kg/m) - distributed load on linear meter rafter leg
Lm (m) - working section of the rafter leg of maximum length
B (cm) - section width
H (cm) - section height
If the value is greater than one, it is necessary to increase the rafter parameters B or H.
Sources used:
- SNiP 2.01.07-85 Loads and impacts with latest changes 2008
- SNiP II-26-76 “Roofs”
- SNiP II-25-80 “Wooden structures”
- SNiP 3.04.01-87 “Insulating and finishing coatings”
- A.A. Savelyev “Rafter systems” 2000
- K-G. Götz, Dieter Hoor, Karl Möhler, Julius Natterer “Atlas of wooden structures”
Creating a project and calculating a truss structure is far from an easy task. A person without minimal experience and knowledge is unlikely to cope with this issue on his own. First of all, the complexity of the calculations lies in a large number of certain factors influencing the roof structure - this is the load from snow and wind, and total weight roofs, and much more.
Therefore, if a person is unsure of his capabilities, then it is advisable to turn to specialists or use computer programs, facilitating the calculation procedure. After all, it’s no secret that from proper roof construction, the further comfort of all inhabitants of the house will depend.
Most often, a rafter system is constructed during the construction of private houses. The basis of most of these roofing structures is a system of wooden beams shaped like a triangle.
It is this form of roof that is considered to be as rigid and durable as possible, and the resulting space between the roof and ceiling forms attic space, which is very often used as an attic or warehouse for old things. Also, by changing the shape of the rafter system, instead of an attic, you can get another room used as an office or an additional living room.
Factors to consider when calculating
Before proceeding directly to the calculations of the truss structure, it is necessary to determine what loads and with what intensity will act on it, depending on the climatic characteristics of the region and the time of year at the place where the house is being built. At the same time, the main natural factors , affecting the roof can be classified according to the following parameters:
The difficulty of carrying out calculations of the rafter system is that it is very difficult for most beginners in the construction business not to miss one of the many types of loads listed above, simultaneously influencing on the roof of the building. This is also due to the fact that when calculating it is necessary to take into account the strength and mass of the rafter legs and the method of their installation and fastening to each other. Although these parameters are secondary, they are no less important and it would be unforgivable to miss them when calculating.
Therefore, to help novice builders, special programs have been developed to facilitate the process of accounting and calculating the design of rafters, although you can also use standard formulas, it all depends on the preferences of the person conducting renovation work. At the same time, very often it is manual calculation and analysis that helps to understand all the design features of the rafters.
How is the constant load on the rafter system calculated?
In order to correctly determine the length of the timber for the rafters and the data on which the main calculations will be based in the future, you first need to calculate the total mass of the roofing “pie”.
For getting final results, it is necessary to calculate the mass of one square meter individual roof layer. In this case, you need to focus on the fact that the average roof consists of the following structural elements:
- Lathing, which consists of small wooden blocks or boards, 25 mm thick. At the same time, the average weight of a square meter of standard sheathing fluctuates within 15 kg.
- A layer of thermal insulation material.
- Roof waterproofing.
- Material used as the main roof covering.
When calculating the total mass of the permanent load, the final result, according to the advice of professional builders, is necessary increase by 10%, which will make it possible to do required stock strength of the future rafter system.
Also, according to the recommendations of professionals, the material of the roofing “pie” should be selected in such a way that general indicators the loads ultimately were no more than 50 kg per meter square roof. Many people consider this load to be too high, but it should be understood that an additional margin of safety is never superfluous. Having completed the calculations of the total mass of the roof, we move on to calculating the load from natural factors.
Calculation of snow loads on the rafter system
The snow load parameter is quite relevant for our climatic conditions, since most regions have a long winter period with constant precipitation. To prevent the roof from deforming, and even worse, from breaking under the weight of the snow layer, it is necessary to include rafters in the structure even at the planning stage, extra strength.
To make the calculations less complicated, specialists derived a generalized formula, which is based on the substitution of coefficients from SNiP. In practice, this formula looks like this: F = P×k, where F means the total load from snow precipitation, P is the mass of the snow layer per square meter of the roof, k is the adjustment factor, which is based on specific factors and design features of the roof.
The mass of a square meter of snow depends on the location of the erected structure. All regions of our state, depending on the intensity of snow precipitation, are divided into certain zones that have their own averages. At the same time, SNiP provides correction factors for each individual roof structure. I would also like to note that this coefficient directly depends on the slope of the roof slope:
- when the roof slope is more than 60°, the correction factor is not used, since with such a slope the snow simply does not linger on the roof;
- if the roof slope angle coefficient ranges from 25 to 60°, this coefficient is 0.7;
- a roof with a minimal, almost flat slope has a maximum correction factor of 1.
Do not forget that the load from snow cover on the rafters may not be entirely uniform, since maximum amount snow accumulates in crevice areas roofing structure and others structural elements roofs. The rafter legs in such places should have a minimum step relative to each other - the most effective option the use of a paired element is considered. In addition, forming a roofing “pie”, potentially problem areas double waterproofing and continuous sheathing are installed.
Calculation of wind load on the rafter system
This type of load is characterized high level criticality, since regardless of the angle of the roof slope, it is exposed to risks from the effects of sharp gusts of wind. At minimum tilt angle Possible roof failure due to the influence of aerodynamic forces. And with a strong roof slope, maximum air flow pressure occurs over the entire area of the roof structure.
To calculate the wind load on rafters, a formula was also developed taking into account a correction factor, which in practice looks like this: V = R×k, while V is the direct value of the wind load, R is the indicator responsible for the region where the building is located, k is the correction factor, as in the case of snow loads.
Regional parameters mean the data given in SNiP, and the correction factor means indicators that take into account the height of the building and the characteristics of the area in which the building is located. In this case, the value of the coefficient itself depends on the following factors:
- for buildings whose height is 20 m, and the building itself is located in an open area, the correction factor is equal to 1.25; if there are artificial or natural obstacles on the territory (other buildings or a line of trees), then the value is reduced to 0.85;
- for buildings with a height of 10 m, an amendment from 0.65 to 1 is used;
- in turn, an adjustment factor from 0.75 to 0.85 is applied in the process of calculating loads on houses less than 5 m in height.
Calculation of the truss structure and rafter leg parameters
To understand what a truss design calculation is, you need to take into account the fact that in reality a rafter system is a set of triangles made of wooden beams, therefore, with the definition rafter lengths There should be no problems, since all mathematical operations are carried out at the level of school geometry.
However for correct calculation For a truss structure, it is important to take into account all load indicators, as well as the size of the spans, the configuration of the sheathing and the specific type of roof itself. To save yourself from additional errors and miscalculations, it is advisable to use special programs that can be found on the Internet.
To calculate the rafters you must use special tables standards. I would like to note that there are ready-made rafter legs that can be purchased at specialized construction stores or in the markets. In this case, the length of the rafter legs will depend on design features structure, and the selection of the rafter section depends on the following parameters:
- length of rafter legs;
- the step with which the rafters will be mounted;
- magnitude of known loads.
It is important to consider that the parameters given in the recommendations are not absolute and subject to change depending on the regional features location of the room. And for correct execution When calculating the rafter leg, the Pythagorean Theorem is used. In this case, the legs will mean the difference in height between the walls of the building and its width, and the hypotenuse will correspond to the length of the rafters.
Programs that make calculations easier
Calculating the rafters of any structure cannot be considered a simple task, for the simple reason that in order to obtain accurate data, it is not easy to correctly operate with the original numbers and special formulas, and also easily navigate SNiP and have minimal drawing skills.
If the above skills do not correspond to the abilities of the person performing the repair, then it is advisable to use free software that can be downloaded on the Internet.
A striking example of such an information product can be called the 3D Max program. At the same time, with minimal computer skills, anyone can handle the software without any problems. In addition, most programs have illustrative examples, facilitating the work with the calculation of the rafter system.
For people who are completely unaware of the intricacies of 3D design, you can download the free Arkon program, which, in addition to the rafter design system, has a calculator designed to calculate parameters rafter legs (section and length of the beam). In addition, the program has the simplest, intellectually understandable interface, greatly simplifying the entire calculation process. I would also like to mention online services for calculating rafter structures, which do not require downloading programs.
A gable roof is complex and large in area. building construction, requiring a professional approach to the design and execution of work. The largest costs go to building materials for rafters, sheathing, insulation, waterproofing, and roofing material. Our gable roof calculator will allow you to calculate the amount of material.
Using a calculator saves time when designing a roof, and your money. The final 2D drawing will guide you through the work, while the 3D rendering will give you an idea of what the roof will look like. Before entering data into the online calculator, you need to have an idea about the elements of the roof.
Rafter parameters
To calculate the rafter system of a gable roof, you need to take into account:
- roof load;
- step between rafters.
- type of roofing
- 100-150 mm with a span length of no more than 5 m, and with additional supports.;
- 150-200 mm with a span length of more than 5 m, with a step of more than 1 m, and if the angle is not large.
Important! The distance between the rafters of a gable roof is usually set at 1 m, but with a roof slope of more than 45 degrees, the pitch of the rafters can be increased to 1.4 m. For flat roofs, the pitch is 0.6-0.8 m.
The rafter legs are attached to the mauerlat, which runs along the perimeter of the house. For it, take either a board with parameters of 50x150 mm, or a beam of 150x150 mm (to distribute the load)
Lathing parameters
For metal tiles, a sparse lathing is created with a board, the width of which is 100 mm, and the thickness is 30 mm. The board is packed in increments that must correspond to the longitudinal axis of the metal tile module - 35 cm (Super Monterrey).
For flexible tiles the sheathing is carried out with a large step, since OSB or plywood will be laid on top of it as a continuous carpet.
Important! When choosing materials, pay attention to moisture resistance and minimum thickness.
When installing warm roofs Between the waterproofing and the roof, a counter-lattice is made with a block, the thickness of which should be 30-50mm.
Roofing parameters
- To calculate the roof of a gable roof, you need to know the dimensions of the roofing material and the amount of overlap.
- Metal tiles for hard roofing are produced in a width of 118 mm (working 110), but the length can be different. The manufacturer can cut any length to order.
- Flexible tiles for soft roof It has different sizes, so you need to look at specific material
- As for the choice of insulation, for Russia the recommended thickness is at least 100 mm, and the correct one would be 150-200 mm.
