A gable roof or gable roof is a roof with two slopes, i.e. having 2 inclined surfaces (slopes) rectangular shape.
Frame gable roof by virtue of design features ideally combines simplicity of design and maintenance with reliability and durability. These and many other parameters make the construction of a gable roof practical and rational decision for private and commercial housing construction.
In this article we will look at how to do rafter system do-it-yourself gable roof. For effective perception of the material, it is presented in the form of step-by-step instructions from A to Z, from selection and calculations, to installation of the Mauerlat and sheathing under the roof. Each stage is accompanied by tables, diagrams, drawings, drawings and photos.
The popularity of the house roof is due to a number of advantages:
- design variability;
- simplicity in calculations;
- naturalness of water flow;
- integrity of the structure reduces the likelihood of leaks;
- efficiency;
- preservation usable area attic or the possibility of arranging an attic;
- high maintainability;
- strength and wear resistance.
Types of gable roof
Installation of the rafter system gable roof depends primarily on its design.
There are several options for gable roofs (types, types):
The most common roof installation option due to its simplicity and reliability. Thanks to symmetry, an even distribution of loads is achieved load-bearing walls and Mauerlat. The type and thickness of the insulation does not affect the choice of material.
The cross-section of the timber makes it possible to provide a reserve bearing capacity. There is no possibility of rafters bending. Supports and struts can be placed almost anywhere.
An obvious drawback is the impossibility of arranging a full attic floor. Due to sharp corners, “dead” zones appear that are unsuitable for use.
The arrangement of one angle of more than 45° leads to a reduction in the amount of unused area. There is an opportunity to do living rooms under the roof. At the same time, the requirements for calculations increase, because the load on the walls and foundation will be distributed unevenly.
This roof design allows you to equip a full second floor under the roof.
Naturally, a simple gable rafter roof differs from a broken line, not only visually. The main difficulty lies in the complexity of the calculations.
Design of a gable roof truss system
Building a roof of any complexity with your own hands requires knowledge of the purpose of the basic structural elements.
The locations of the elements are shown in the photo.
- Mauerlat. Designed to distribute the load from the rafter system onto the load-bearing walls of the building. To arrange the Mauerlat, a timber made of durable wood is selected. Preferably larch, pine, oak. The cross-section of the timber depends on its type - solid or glued, as well as on the expected age of the structure. The most popular sizes are 100x100, 150x150 mm.
Advice. For a metal rafter system, the Mauerlat must also be metal. For example, a channel or an I-profile.
- Rafter leg. The main element of the system. To make rafter legs, a strong beam or log is used. The legs connected at the top form a truss.
Silhouette roof truss determines the appearance of the building. Examples of farms in the photo.
The parameters of the rafters are important. They will be discussed below.
- Puff- connects rafter legs and gives them rigidity.
- Run:
- Ridge run, is mounted at the junction of one rafter to another. In the future, the roof ridge will be installed on it.
- Side purlins, they provide the truss with additional rigidity. Their number and size depend on the load on the system.
- Rafter stand- vertically located beam. It also takes on part of the load from the weight of the roof. In a simple gable roof it is usually located in the center. With a significant span width - in the center and on the sides. In an asymmetrical gable roof, the installation location depends on the length of the rafters. With a broken roof and arrangement of one room per attic attic- the racks are located on the sides, leaving free space for moving. If there are supposed to be two rooms, the racks are located in the center and on the sides.
The location of the rack depending on the length of the roof is shown in the figure.
- Strut. Serves as a support for the stand.
Advice. Installing the brace at an angle of 45° significantly reduces the risk of deformation from wind and snow load.
In regions with significant wind and snow loads, not only longitudinal struts are installed (located in the same plane as the rafter pair), but also diagonal ones.
- Sill. Its purpose is to serve as a support for the rack and a place for attaching the strut.
- Lathing. Designed for movement during construction work and fixation of roofing material. Installed perpendicular to the rafter legs.
Advice. An important purpose of the sheathing is to redistribute the load from the roofing material to the rafter system.
Having a drawing and diagram indicating the location of all the listed structural elements will help in the work.
Advice. Be sure to add information about the passage structure to the gable roof rafter system diagram ventilation shaft and chimney.
The technology of their installation is determined by the type of roof.
Selection of material for rafters
When calculating the material for a gable roof, you need to choose high-quality wood without damage or wormholes. The presence of knots for beams, mauerlat and rafters is not allowed.
For sheathing boards, there should be a minimum of knots, and they should not fall out. The wood must be durable and treated with the necessary preparations that will increase its properties.
Advice. The length of the knot should not exceed 1/3 of the thickness of the timber.
Calculation of the rafter system of a gable roof
Calculation of material parameters important stage, so we present the calculation algorithm step by step.
It is important to know: the entire rafter system consists of many triangles, as the most rigid element. In turn, if the stingrays have different shape, i.e. are an irregular rectangle, then you need to divide it into separate components and calculate the load and amount of materials for each. After calculations, summarize the data.
1. Calculation of the load on the rafter system
The load on the rafters can be of three types:
- Constant loads. Their action will always be felt by the rafter system. Such loads include the weight of the roof, sheathing, insulation, films, additional roofing elements, finishing materials For . The weight of the roof is the sum of the weight of all its constituent elements; such a load is easier to take into account. On average, the constant load on the rafters is 40-45 kg/sq.m.
Advice. To make a safety margin for the rafter system, it is better to add 10% to the calculation.
For reference: The weight of some roofing materials per 1 sq.m. presented in the table
Advice. It is desirable that the weight of roofing material per 1 sq.m. roof area did not exceed 50 kg.
- Variable loads. They act at different times and with different strengths. Such loads include: wind load and its strength, snow load, precipitation intensity.
In essence, the roof slope is like a sail and, if you take into account the wind load, the entire roof structure can be destroyed.
The calculation is carried out according to the formula: wind load is equal to the regional indicator multiplied by correction factor. These indicators are contained in SNiP “Loads and Impacts” and are determined not only by the region, but also by the location of the house. For example, on a private house surrounded by multi-story buildings, there is less load. A detached country house or cottage experiences increased wind loads.
2. Calculation of snow load on the roof
The roof calculation for snow load is carried out according to the formula:
The total snow load is equal to the weight of the snow multiplied by the correction factor. The coefficient takes into account wind pressure and aerodynamic influence.
The weight of snow that falls on 1 square meter. roof area (according to SNiP 2.01.07-85) is in the range of 80-320 kg/sq.m.
Coefficients showing the dependence on the slope angle are shown in the photo.
Nuance. When the slope angle is over 60 ° the snow load does not affect the calculation. Because the snow will quickly slide down and will not affect the strength of the beam.
- Special loads. Accounting for such loads is carried out in places with high seismic activity, tornadoes, and storm winds. For our latitudes, it is enough to make a safety margin.
Nuance. The simultaneous action of many factors causes a synergy effect. This is worth considering (see photo).
Assessment of the condition and load-bearing capacity of walls and foundations
It should be borne in mind that the roof has significant weight, which can cause damage to the rest of the building.
Determining the roof configuration:
- simple symmetrical;
- simple asymmetrical;
- broken line
How more complex form roof, the greater the number of trusses and sub-rafter elements needed to create the necessary safety margin.
The angle of inclination of a gable roof is determined primarily by the roofing material. After all, each of them puts forward their own demands.
- soft roof - 5-20°;
- metal tiles, slate, corrugated sheets, ondulin - 20-45°.
It should be noted that increasing the angle increases the area of space under the roof, but also the amount of material. What affects the total cost of work.
Nuance. The minimum angle of inclination of a gable roof must be at least 5°.
5. Calculation of rafter pitch
The pitch of the gable roof rafters for residential buildings can range from 60 to 100 cm. The choice depends on the roofing material and the weight of the roof structure. Then the number of rafter legs is calculated by dividing the length of the slope by the distance between the rafter pairs plus 1. The resulting number determines the number of legs per slope. For the second, the number must be multiplied by 2.
The length of the rafters for the attic roof is calculated using the Pythagorean theorem.
Parameter "a"(roof height) is set independently. Its value determines the possibility of arranging a living space under the roof, the convenience of being in the attic, and the consumption of material for the construction of the roof.
Parameter "b" equal to half the width of the building.
Parameter "c" represents the hypotenuse of the triangle.
Advice. To the obtained value you need to add 60-70 cm for cutting and moving the rafter leg beyond the wall.
It is worth noting that the maximum length of the timber is 6 m.p. Therefore, if necessary, the timber for the rafters can be spliced (extension, joining, joining).
The method of splicing rafters along the length is shown in the photo.
The width of the roof rafters depends on the distance between opposite load-bearing walls.
7. Calculation of the rafter cross-section
The cross-section of the rafters of a gable roof depends on several factors:
- loads, we have already written about it;
- type of material used. For example, a log can withstand one load, timber - another, laminated timber - a third;
- rafter leg lengths;
- the type of wood used in construction;
- distances between rafters (rafter pitch).
You can determine the cross-section of the beam for the rafters, knowing the distance between the rafters and the length of the rafters using the data below.
Rafter cross-section - table
Advice. The larger the installation pitch of the rafters, the greater the load on one rafter pair. This means that the cross-section of the rafters needs to be increased.
Dimensions of lumber (timbers and boards) for a gable rafter system:
- thickness (section) of the Mauerlat - 10x10 or 15x15 cm;
- the thickness of the rafter leg and tie is 10x15 or 10x20 cm. Sometimes a beam of 5x15 or 5x20 cm is used;
- run and strut - 5x15 or 5x20. Depending on the width of the foot;
- stand - 10x10 or 10x15;
- bench - 5x10 or 5x15 (depending on the width of the rack);
- thickness (section) of the roof sheathing - 2x10, 2.5x15 (depending on the roofing material).
Types of gable roof rafter system
For the roof structure under consideration, there are 2 options: layered and hanging rafters.
Let's consider each type in detail in order to make an informed choice.
Hanging rafters
They are used for roof widths of no more than 6 lm. Installation of hanging rafters is carried out by attaching the legs to the load-bearing wall and the ridge girder. The design of hanging rafters is special in that the rafter legs are under the influence of a bursting force. Hanging rafters with a tie installed between the legs reduce its impact. The tie in the rafter system can be wooden or metal. Often the puffs are placed at the bottom, then they play a role load-bearing beams. It is important to ensure reliable fastening tightening on the rafter leg. Because a bursting force is also transmitted to it.
Advice.
The higher the tightening is located, the greater strength it should have.
If the tightening is not installed, the load-bearing walls may simply “move apart” from the pressure created by the rafter system.
Layered rafters
They are used for arranging roofs of any size. The design of layered rafters provides for the presence of a beam and a stand. The bench lying parallel to the Mauerlat takes on part of the load. Thus, the rafter legs are, as it were, inclined towards each other and supported by a stand. The rafter legs of the layered system work only in bending. And the ease of installation also tips the scales in their favor. The only drawback is the presence of a stand.
Combined
Due to the fact that modern roofs are distinguished by a wide variety of shapes and complexity of configurations, used combined view rafter system.
After choosing the type of rafter system, you can accurately calculate the amount of materials. Write down the calculation results. At the same time, professionals recommend drawing up drawings for each roof element.
Installation of a gable roof rafter system
After the gable roof rafters have been calculated, installation can begin. We will divide the process into stages and give a description of each of them. The result will be a kind of step-by-step instructions containing additional information on each stage.
1. Attaching the Mauerlat to the wall
The beam is installed along the length of the wall on which the rafters will rest.
In log houses, the role of the mauerlat is played by the upper crown. In buildings built from porous material (aerated concrete, foam concrete) or brick, the Mauerlat is installed along the entire length of the load-bearing wall. In other cases, it can be installed between the rafter legs.
Material prepared for the website www.site
Since the length of the Mauerlat exceeds the standard dimensions of lumber, it has to be spliced.
The connection of the Mauerlat to each other is done as shown in the figure.
How to connect the Mauerlat?
The beams are cut only at an angle of 90°. Connections are made using bolts. Nails, wire, wooden dowels are not used.
How to attach the Mauerlat?
The Mauerlat is installed at the top of the wall. The installation technology provides several ways to attach the Mauerlat:
- strictly in the center of the load-bearing wall;
- with a shift to one side.
Advice.
The Mauerlat cannot be placed closer than 5 cm to the outer edge of the wall.
To protect the timber for the Mauerlat from damage, it is laid on a layer of waterproofing material, which most often is ordinary roofing felt.
Reliability of Mauerlat fastening important aspect construction. This is due to the fact that the roof slope is like a sail. That is, it experiences strong wind load. Therefore, the Mauerlat must be firmly fixed to the wall.
Methods for attaching the Mauerlat to the wall and rafters
Anchor bolts. Ideal for monolithic structures.
Wooden dowels. Used for log houses and beams. But, they are always used with additional fasteners.
Staples.
Stud or fittings. It is used if the cottage is built from porous materials (aerated concrete, foam concrete).
Sliding mount (hinge). Tying in this way allows for the displacement of the rafter legs when the house shrinks.
Annealed wire (knitting, steel). Used as additional fastening In most cases.
2. Manufacturing of trusses or pairs
Installation is carried out in two ways:
- installation of beams directly on the roof. It is not used often, since it is problematic to carry out all the work, measurements, and trimming at height. But it allows you to completely do the installation yourself;
- assembly on the ground. That is, individual elements (triangles or pairs) for the rafter system can be assembled below and then raised to the roof. The advantage of such a system is faster execution high-altitude work. The disadvantage is that the weight of the assembled truss structure can be significant. To lift it you will need special equipment.
Advice. Before assembling the rafter legs, you need to apply markings. It is very convenient to use templates for these purposes. The rafter pairs assembled according to the template will be absolutely identical. To make a template, you need to take two boards, the length of each of which is equal to the length of one rafter, and connect them together.
3. Installation of rafter legs
The assembled pairs rise to the top and are installed on the Mauerlat. To do this, you need to make a gash at the bottom of the rafter legs.
Advice. Since the slots on the Mauerlat will weaken it, you can only make cuts on the rafter leg. To ensure that the cut is uniform and fits tightly to the base, you need to use a template. It is cut out of plywood.
Methods of fastening the rafter leg are shown in the figure.
Start installation rafter pairs needed from opposite ends of the roof.
Advice. To correctly install the rafter legs, it is better to use temporary struts and spacers.
A string is stretched between the fixed pairs. It will simplify the installation of subsequent rafter pairs. It will also indicate the level of the ridge.
If the rafter system is mounted directly on the roof of the house, then after installing the two outer rafter legs, the ridge support is installed. Next, the halves of the rafter pair are attached to it.
It is worth noting that the opinions of professionals differ on this issue. Some advise using a staggered fastening pattern, which will allow the increasing load to be distributed more evenly on the walls and foundation. This order involves installing one rafter in a checkerboard pattern. After part of the rafter legs is installed, the missing parts of the pair are mounted. Others insist that it is necessary to mount each pair in a sequential manner. Depending on the size of the structure and the configuration of the truss, the rafter legs are reinforced with supports and racks.
Nuance. Connect additional elements structures using cutting. It is preferable to fix them with construction staples.
If necessary, you can lengthen the rafter leg.
Methods for splicing rafter legs are shown in the photo.
Advice. The method by which the mauerlat is lengthened (cut at 90°) cannot be used in this case. This will weaken the rafter.
4. Installing the ridge of a gable roof
The roof ridge unit is made by connecting the rafter legs at the top.
Roof ridge structure:
- Method without using a support beam (see figure).
- Method using rafter beams. Timber is needed for large roofs. In the future, it can become a support for the rack.
- Method of laying on timber.
- More modern variety The method shown in the photo can be considered for making a ridge assembly.
- Cutting method.
After the rafter system is installed, we perform major fastening of all structural elements.
5. Installation of roof sheathing
The sheathing is installed in any case, and is designed for more convenient movement along the roof during work, as well as for fastening roofing material.
The sheathing pitch depends on the type of roofing material, for example:
- for metal tiles - 350 mm (the distance between the two lower boards of the sheathing should be 300 mm).
- for corrugated sheets and slate - 440 mm.
- under soft roof We lay a continuous sheathing.
Rafter system of a gable roof with an attic - video:
Conclusion
As you can see, despite its apparent simplicity, the installation of a gable roof rafter system contains many pitfalls. But, based on the recommendations given, you can build without any problems reliable design with your own hands.
The calculation of the rafter system should be done not after the construction of the house frame, but at the stage of preparing the building project. We must remember that for very important and prestigious buildings, it is recommended to order such work from professional architects, only they will be able to carry out correct calculations and guarantee the duration and safety of operation of the structure.
Although this is one of the simplest types of systems for residential buildings, there are several types of design. Diversity allows you to increase the options for using roofs when building houses according to standard or individual exclusive projects.
| Type of gable roof truss system | Architectural features and brief description |
|---|---|
| The most commonly used option has two completely identical rectangular slopes. Loads between individual elements are distributed evenly regardless of their location. The number of additional stops is not limited; the specific decision is made depending on the plans for using the attic space. Calculations can be done using free programs posted on construction sites. |
| The ridge is shifted to one side of the house or slopes from different angles tilt The roof truss system is more complex to calculate. If in a simplified version it is possible to calculate one slope and automatically apply the obtained data to the second, then this option cannot be used for an asymmetrical rafter system. Advantages: original appearance. Disadvantages are the complexity of calculations and installation and the reduction in usable attic space. |
| Most often used during construction attic premises, allows you to significantly increase the volume of attic space. The calculations are of medium complexity. Rafter system with external bend. It is rare to find systems with an internal fracture other than the original one. appearance, they have no advantages. |
Structural elements of the rafter system
We will give a list of all the elements that need to be calculated for each specific case.
The simplest element of the rafter system can be made from timber 150×150mm, 200×200mm or boards 50×150mm and 50×200mm. On small houses It is allowed to use paired boards with a thickness of 25mm or more. The Mauerlat is considered an unimportant element; its task is only to evenly distribute point forces from the rafter legs around the perimeter façade walls buildings. It is fixed to the wall on a reinforcing belt using anchors or large dowels. Some rafter systems have large expansion forces; in these cases, the element is designed for stability. Accordingly, they are selected optimal ways fixing the Mauerlat to the walls, taking into account the material of their masonry.
Prices for timber
They form the silhouette of the rafter system and perceive everything effective loads: from wind and snow, dynamic and static, permanent and temporary.
They are made from boards 50×100 mm or 50×150 mm, and can be solid or extended.
The boards are calculated based on their bending resistance, and taking into account the data obtained, wood species and types, the distance between the legs, and additional elements to increase stability are selected. The two connected legs are called a truss and may have tie-rods at the top.
Tightenings are calculated for tension.
Runs
Some of the most important elements rafter system of a gable roof. They are designed for maximum bending forces and are made of boards or timber with a section corresponding to the loads. A ridge girder is installed in the highest place; side girders can be mounted on the sides. Run calculations are quite complex and must take into account a large number of factors.
Can be vertical or inclined. Inclined ones work in compression and are attached at right angles to the rafters. The lower part rests against the floor beams or concrete plates, acceptable options for support o horizontal beds. Due to the stops, it is possible to use thinner lumber to make rafter legs. Vertical stops work for compression, horizontal stops for bending.
Lezhny
They are laid along the attic, resting against several load-bearing walls or interior partitions. Purpose – to simplify the manufacture of a complex rafter system, to create new points for transferring loads from various types stops For the beds, you can use beams or thick boards; the calculation is made based on the maximum bending moment between the support points.
Lathing
The type of lathing is selected taking into account technical parameters roofing coverings and does not affect the performance of the rafter system.
What type of lathing is needed for corrugated sheeting? When to install wood and when to install metal? How to choose the right lathing pitch and what factors to consider?
Prices for construction boards
Construction boards
Stages of calculating a gable roof
All work consists of several stages, each big influence on the stability and durability of the structure.
Calculation of parameters of rafter legs
Based on the data obtained, the linear parameters of the lumber and the pitch of the trusses are determined. If the loads on the rafters are very large, then vertical or angular stops are installed to distribute them evenly, and the calculations are repeated taking into account new data. The direction of influence of forces, the magnitude of torque and bending moments change. During calculations, three types of loads must be taken into account.
- Permanent. These loads include the weight of roofing materials, sheathing, and insulating layers. If attic space exploited, then the weight of all finishing materials should be taken into account internal surfaces walls Data on roofing materials is taken from their technical characteristics. Easiest of all metal roofs, the heaviest of all are natural slate materials, ceramic or cement-sand tiles.
- Variable loads. The most difficult efforts to calculate, especially now, when the climate is changing dramatically. For calculations, data is still taken from outdated SNiP reference books. For his tables, information from fifty years ago was used; since then, the height of the snow cover, the strength and the prevailing direction of the wind have changed significantly. Snow loads can be several times higher than those in the tables, which has a significant impact on the reliability of calculations.
Moreover, the snow height changes not only taking into account climate zone, but also depending on the location of the house in the cardinal directions, the terrain, the specific location of the building, etc. Data on the strength and direction of the wind are also unreliable. Architects have found a way out of this difficult situation: data is taken from outdated tables, but to ensure reliability and stability, a safety factor is used in each formula. For critical rafter systems on residential buildings, the standard is 1.4. This means that all linear parameters of the system elements increase by 1.4 times and due to this, the reliability and safety of the structure’s operation increases.
The actual wind load is equal to the indicator in the region where the structure is located, multiplied by the correction factor. The correction factor characterizes the location of the building. The same formula is used to determine the maximum snow load.
- Individual loads. This category includes specific forces that affect the rafter system of a gable roof during an earthquake, tornado and other natural disasters.
The final values are determined taking into account the probability of simultaneous action of all the above loads. The dimensions of each element of the rafter system are calculated using a safety factor. Using the same algorithm, not only rafter legs are designed, but also lintels, stops, braces, purlins and other roof elements.
The main element of the roof, which absorbs and resists all types of loads, is rafter system. Therefore, in order for your roof to reliably withstand all impacts environment, it is very important to do correct calculation rafter system.
To independently calculate the characteristics of the materials required for installing the rafter system, I provide simplified calculation formulas. Simplifications have been made to increase the strength of the structure. This will cause a slight increase in lumber consumption, but on small roofs of individual buildings it will be insignificant. These formulas can be used when calculating gable attic and mansard roofs, as well as single-pitch roofs.
Based on the calculation methodology given below, programmer Andrey Mutovkin (Andrey’s business card - mutovkin.rf) for his own needs developed a rafter system calculation program. At my request, he generously allowed me to post it on the site. You can download the program.
The calculation methodology is based on SNiP 2.01.07-85 “Loads and Impacts”, taking into account “Changes...” from 2008, as well as on the basis of formulas given in other sources. I developed this technique many years ago, and time has confirmed its correctness.
To calculate the rafter system, first of all, it is necessary to calculate all the loads acting on the roof.
I. Loads acting on the roof.
1. Snow loads.
2. Wind loads.
In addition to the above, the rafter system is also subject to loads from roof elements:
3. Roof weight.
4. Weight of rough flooring and sheathing.
5. Weight of insulation (in the case of an insulated attic).
6. The weight of the rafter system itself.
Let's consider all these loads in more detail.
1. Snow loads.
To calculate the snow load we use the formula:
Where,
S - desired value of snow load, kg/m²
µ - coefficient depending on the roof slope.
Sg - standard snow load, kg/m².
µ - coefficient depending on the roof slope α. Dimensionless quantity.
The roof slope angle α can be approximately determined by dividing the height H by half the span - L.
The results are summarized in the table:
Then, if α is less than or equal to 30°, µ = 1 ;
if α is greater than or equal to 60°, µ = 0;
If 30° is calculated using the formula:
µ = 0.033·(60-α);
Sg - standard snow load, kg/m².
For Russia it is accepted according to map 1 of mandatory appendix 5 of SNiP 2.01.07-85 “Loads and impacts”
For Belarus, the standard snow load Sg is determined
Technical code of PRACTICE Eurocode 1. EFFECTS ON STRUCTURES Part 1-3. General impacts. Snow loads. TKP EN1991-1-3-2009 (02250).
For example,
Brest (I) - 120 kg/m²,
Grodno (II) - 140 kg/m²,
Minsk (III) - 160 kg/m²,
Vitebsk (IV) - 180 kg/m².
Find the maximum possible snow load on a roof with a height of 2.5 m and a span of 7 m.
The building is located in the village. Babenki Ivanovo region. RF.
Using Map 1 of Mandatory Appendix 5 of SNiP 2.01.07-85 “Loads and Impacts” we determine Sg - the standard snow load for the city of Ivanovo (IV district):
Sg=240 kg/m²
Determine the roof slope angle α.
To do this, divide the roof height (H) by half the span (L): 2.5/3.5=0.714
and from the table we find the slope angle α=36°.
Since 30°, the calculation µ will be produced using the formula µ = 0.033·(60-α) .
Substituting the value α=36°, we find: µ = 0.033·(60-36)= 0.79
Then S=Sg·µ =240·0.79=189kg/m²;
the maximum possible snow load on our roof will be 189 kg/m².
2. Wind loads.
If the roof is steep (α > 30°), then due to its windage, the wind puts pressure on one of the slopes and tends to overturn it.
If the roof is flat (α, then the lifting aerodynamic force that arises when the wind bends around it, as well as turbulence under the overhangs, tend to lift this roof.
According to SNiP 2.01.07-85 “Loads and impacts” (in Belarus - Eurocode 1 IMPACTS ON STRUCTURES Part 1-4. General impacts. Wind impacts), the standard value of the average component of the wind load Wm at a height Z above the ground surface should be determined by the formula :
Where,
Wo is the standard value of wind pressure.
K is a coefficient that takes into account the change in wind pressure with height.
C - aerodynamic coefficient.
K is a coefficient that takes into account the change in wind pressure with height. Its values, depending on the height of the building and the nature of the terrain, are summarized in Table 3.
C - aerodynamic coefficient,
which, depending on the configuration of the building and the roof, can take values from minus 1.8 (the roof rises) to plus 0.8 (the wind presses on the roof). Since our calculation is simplified in the direction of increasing strength, we take the value of C equal to 0.8.
When building a roof, it must be remembered that wind forces tending to lift or tear off the roof can reach significant values, and therefore, the bottom of each rafter leg must be properly attached to the walls or mats.
This can be done by any means, for example, using annealed (for softness) steel wire with a diameter of 5 - 6 mm. With this wire, each rafter leg is screwed to the matrices or to the ears of the floor slabs. It's obvious that The heavier the roof, the better!
Determine the average wind load on the roof one-story house with the height of the ridge from the ground - 6 m. , slope angle α=36° in the village of Babenki, Ivanovo region. RF.
According to map 3 of Appendix 5 in “SNiP 2.01.07-85” we find that the Ivanovo region belongs to the second wind region Wo= 30 kg/m²
Since all buildings in the village are below 10m, coefficient K= 1.0
The value of the aerodynamic coefficient C is taken equal to 0.8
standard value of the average component of the wind load Wm = 30 1.0 0.8 = 24 kg/m².
For information: if the wind blows at the end of a given roof, then a lifting (tearing) force of up to 33.6 kg/m² acts on its edge
3. Roof weight.
Different types of roofing have the following weight:
1. Slate 10 - 15 kg/m²;
2. Ondulin (bitumen slate) 4 - 6 kg/m²;
3. Ceramic tiles 35 - 50kg/m²;
4. Cement-sand tiles 40 - 50 kg/m²;
5. Bituminous shingles 8 - 12 kg/m²;
6. Metal tiles 4 - 5 kg/m²;
7. Corrugated sheeting 4 - 5 kg/m²;
4. Weight of rough flooring, sheathing and rafter system.
The weight of the rough flooring is 18 - 20 kg/m²;
Sheathing weight 8 - 10 kg/m²;
The weight of the rafter system itself is 15 - 20 kg/m²;
When calculating the final load on the rafter system, all of the above loads are summed up.
And now I'll tell you little secret. Sellers of certain types of roofing materials as one of the positive properties note their lightness, which, according to them, will lead to significant savings in lumber in the manufacture of the rafter system.
To refute this statement, I will give the following example.
Calculation of the load on the rafter system when using various roofing materials.
Let's calculate the load on the rafter system when using the heaviest one (Cement-sand tiles
50 kg/m²) and the lightest (Metal tile 5 kg/m²) roofing material for our house in the village of Babenki, Ivanovo region. RF.
Cement-sand tiles:
Wind loads - 24kg/m²
Roof weight - 50 kg/m²
Sheathing weight - 20 kg/m²
Total - 303 kg/m²
Metal tiles:
Snow load - 189kg/m²
Wind loads - 24kg/m²
Roof weight - 5 kg/m²
Sheathing weight - 20 kg/m²
The weight of the rafter system itself is 20 kg/m²
Total - 258 kg/m²
Obviously, the existing difference in design loads (only about 15%) cannot lead to any significant savings in lumber.
So, with the calculation of the total load Q acting on square meter We figured out the roof!
I especially draw your attention: when making calculations, pay close attention to the dimensions!!!
II. Calculation of the rafter system.
Rafter system consists of separate rafters (rafter legs), so the calculation comes down to determining the load on each rafter leg separately and calculating the cross-section of an individual rafter leg.
1. Find the distributed load per linear meter of each rafter leg.
Where
Qr - distributed load per linear meter of rafter leg - kg/m,
A - distance between rafters (rafter pitch) - m,
Q is the total load acting on a square meter of roof - kg/m².
2. Determine the working area in the rafter leg maximum length Lmax.
3. We calculate the minimum cross-section of the rafter leg material.
When choosing material for rafters, we are guided by the table standard sizes lumber (GOST 24454-80 Lumber coniferous species. Dimensions), which are summarized in Table 4.
| 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 |
A. We calculate the cross-section of the rafter leg.
We arbitrarily set the width of the section in accordance with standard dimensions, and determine the height of the section using the formula:
H ≥ 8.6 Lmax sqrt(Qr/(BRben)), if the roof slope α
H ≥ 9.5 Lmax sqrt(Qr/(BRben)), if the roof slope α > 30°.
H - section height cm,
B - section width cm,
Rbend - bending resistance of wood, kg/cm².
For pine and spruce Rben is equal to:
1st grade - 140 kg/cm²;
2nd grade - 130 kg/cm²;
3rd grade - 85 kg/cm²;
sqrt - square root
B. We check whether the deflection value is within the standard.
The normalized deflection of the material under load for all roof elements should not exceed L/200. Where, L is the length of the working section.
This condition is satisfied if the following inequality is true:
3.125 Qr (Lmax)³/(B H³) ≤ 1
Where,
Qr - distributed load per linear meter of rafter leg - kg/m,
Lmax - working section of the rafter leg with maximum length m,
B - section width cm,
H - section height cm,
If the inequality is not met, then increase B or H.
Condition:
Roof pitch angle α = 36°;
Rafter pitch A= 0.8 m;
The working section of the rafter leg of maximum length Lmax = 2.8 m;
Material - 1st grade pine (Rbending = 140 kg/cm²);
Roofing - cement-sand tiles (Roofing weight - 50 kg/m²).
As it was calculated, the total load acting on a square meter of roof is Q = 303 kg/m².
1. Find the distributed load per linear meter of each rafter leg Qr=A·Q;
Qr=0.8·303=242 kg/m;
2. Choose the thickness of the board for the rafters - 5cm.
Let's calculate the cross-section of the rafter leg with a section width of 5 cm.
Then, H ≥ 9.5 Lmax sqrt(Qr/BRben), since the roof slope α > 30°:
H ≥ 9.5 2.8 sqrt(242/5 140)
H ≥15.6 cm;
From the table of standard sizes of lumber, select a board with the closest cross-section:
width - 5 cm, height - 17.5 cm.
3. We check whether the deflection value is within the standard. To do this, the following inequality must be observed:
3.125 Qr (Lmax)³/B H³ ≤ 1
Substituting the values, we have: 3.125·242·(2.8)³ / 5·(17.5)³= 0.61
Meaning 0.61, which means the cross-section of the rafter material is chosen correctly.
The cross-section of the rafters, installed in increments of 0.8 m, for the roof of our house will be: width - 5 cm, height - 17.5 cm.
The roof of a building is designed to hold external loads and redistribute them to load-bearing walls or supporting structures. These loads include weight roofing pie, the mass of the structure itself, the weight of the snow cover, and so on.
The roof is located on the rafter system. So called frame construction, on which the roof is fixed. It accepts all external loads, distributing them across supporting structures.
The rafter system of a gable roof includes the following elements:
- Mauerlat;
- Struts and braces;
- Lateral and ridge purlins;
- Rafter legs.
A rafter truss is a structure that includes all of the listed elements with the exception of the Mauerlat.
Calculation of gable roof loads
Constant loads
The first type refers to those loads that always act on the roof (in any season, time of day, and so on). These include the weight of the roofing pie and various equipment installed on the roof. For example, the weight of a satellite dish or aerator. It is necessary to calculate the weight of all truss structure along with fasteners and various elements. To perform this task, professionals use computer programs, as well as special calculators.
Calculation gable roof is based on calculating the loads on the rafter legs. First of all, you need to determine the weight of the roofing cake. The task is quite simple, you just need to know the materials used, as well as the dimensions of the roof.
As an example, let’s calculate the weight of a roofing cake with ondulin material. All values are taken approximately high accuracy not required here. Usually builders perform calculations of the weight per square meter of roofing. And then this figure is multiplied by the total roof area.
The roofing pie consists of ondulin, a layer of waterproofing (in this case - insulation on a polymer-bitumen basis), a layer of thermal insulation (weight calculation will be carried out basalt wool) and lathing (the thickness of the boards is 25 mm). Let's calculate the weight of each element separately, and then add up all the values.
Calculation of the roof of a gable roof:
- A square meter of roofing material weighs 3.5 kg.
- A square meter of waterproofing layer weighs 5 kg.
- A square meter of insulation weighs 10 kg.
- A square meter of sheathing weighs 14 kg.
Now let's calculate the total weight:
3.5 + 5 + 10 + 14 = 32.5
The resulting value must be multiplied by the correction factor (in this case it is equal to 1.1).
32.5 * 1.1 = 35.75 kg
It turns out that a square meter of roofing cake weighs 35.75 kg. All that remains is to multiply this parameter by the roof area, then you can calculate a gable roof.
Variable roof loads
Variable loads are those that act on the roof not constantly, but seasonally. A striking example is snow in winter. Snow masses settle on the roof, creating additional impact. But in the spring they melt, and accordingly, the pressure decreases.
Variable loads also include wind. This is also a weather phenomenon that does not always work. And there are many such examples. Therefore, it is important to take into account variable loads when calculating the length of the rafters of a gable roof. When calculating, you need to take into account many different factors affecting the roof of a building.
Now let's take a closer look at snow loads. When calculating this parameter, you need to use a special map. The mass of snow cover is marked there different regions countries.
To calculate this type of load, the following formula is used:
Where Sg is the terrain indicator taken from the map, and µ is the correction factor. It depends on the roof slope: the stronger the slope, the lower the correction factor. And here there is important nuance- for roofs with a slope of 60 o or more it is not taken into account at all. After all, the snow will simply roll off of them, and not accumulate.
The whole country is divided into regions not only by the mass of snow, but also by the strength of the winds. Available special card, where you can find out this indicator in a certain area.
When calculating roof rafters, wind loads are determined using the following formula:
Where x is the correction factor. It depends on the location of the building and its height. And W o is the parameter selected from the map.
Calculation of the dimensions of the rafter system
When the calculation of all types of loads is finished, you can proceed to calculating the dimensions of the rafter system. The work performed will differ depending on what kind of roof structure is planned.
In this case, a gable one is considered.
Section of the rafter leg
The calculation of the rafter leg is based on 3 criteria:
- Loads from previous section;
- Remoteness of the railings;
- Rafter length.
There is a special table of sections of rafter legs, in which you can find out this indicator based on the criteria described above.
Length of rafters in a gable roof
Manual calculations will require basic knowledge of geometry, in particular the Pythagorean theorem. The rafter is the hypotenuse of a right triangle. Its length can be found by dividing the length of the leg by the cosine of the opposite angle.
Let's look at a specific example:
It is required to calculate the length of the rafters of a gable roof for a house with a width of 6 m, in which the slope of the slopes is 45 o. Let L be the length of the rafters. Let's substitute all the data into the formula.
L = 6 / 2 / cos 45 ≈ 6 / 2 / 0.707 ≈ 4.24 meters.
You need to add the length of the visor to the resulting value. It is approximately 0.5 m.
4.24 + 0.5 = 4.74 meters.
This completes the calculation of the length of the rafters for a gable roof. It was manual method completing the task. There are special computer programs designed to automate this process. The easiest way is to use Arkon. This is a completely free program that even a person with little computer knowledge can easily understand.
It is enough to simply specify the input parameters based on the size of the house. The program will independently perform calculations and show the required cross-section, as well as the length of the gable roof rafters.
The roof is one of the main elements of the roof, which takes on all the impacts coming from the atmosphere.
The main function is to drain water and disperse the load on the top of the building after snow falls.
High-quality roofing is valued for long-term operation and nice appearance.
Online roof calculation (calculator with drawings) - will help you make a reliable calculation of the amount of roofing, rafters and sheathing.
In construction there are several types of coatings, which in turn are further divided into subspecies. The most common building surfaces include flat(can be exploited or unexploited) and attic(this includes a whole group of roofs: conical, conical and others). Without a doubt, when it comes to choosing the type of roof, further determination of the surface material becomes relevant.
Among the most popular types are mentioned:
- , aluminum seam and other metal roofing;
- slate coating;
- roof made from natural materials.
Roofing materials
Included in the rafter system includes many construction “spare parts”, but the main ones in this wide list are:
- slopes (inclined planes),
- sheathing,
- rafters,
- Mauerlat beam.
In addition, a gutter, aerator, drainage pipe and others play a certain role in the process of covering and further functioning of the roof.
The rafter system is presented in the form of a supporting system, which is based on inclined rafter legs, vertical racks, as well as inclined struts. In some cases, it becomes necessary to use rafter beams to “bind” the rafter legs. There are hanging and layered rafters. In the first group, trusses with sleepers are separately distinguished.
Roofing device
The next layer in the design mansard roof the sheathing serves, which is laid over the legs of the rafter system. This creates a certain foundation for the roofing, and also significantly expands the spatial component of the eaves. Most often, this element is made of either wood or metal.
The Mauerlat also adheres to its niche of responsibility. It functions as a support for the rafters along the edges, and lay it on outer wall along the perimeter. The beam is usually lumber (that is, made of wood), but it is quite reasonable if, in the case of a special metal frame, similar contents will be used to prepare the mauerlat.
Roof calculation online calculator
How to calculate the roof of a house and how to calculate the material for the roof quickly and without errors? A specially designed service can help you with this - construction calculator for calculating the roof of a private house. The calculator calculates the quantity, weight, and much more.
Calculator field designations
Specify roofing material:
Select a material from the list -- Slate (wavy 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) From galvanized sheet (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 weight 1 square meter of coverage (? 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)
Working area of the 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 of roofing material: 0 kg.
Number of rolls of 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 standard length 6 meters: 0 pcs.
Volume of sheathing boards: 0 m3.
Approximate weight of sheathing boards: 0 kg.
Snow load region
Decoding calculator fields
Loads acting on the roof
It is likely that when it comes to choosing the type of roof and roofing, you should be guided by more than just visual requirements. First of all, it is necessary to pay attention to studying the issue of load on the hip.
NOTE!
The roof is affected not only by precipitation and its volumes- temperature instability and all sorts of reasons of physical and mechanical origin also exert serious pressure on the surface.
There are many reasons and sources of impact, but the leading ones are snow and wind. What can we say if building codes require mandatory calculations for the future canopy. The calculation is bright strong personality due to differences in the amount of snow cover that falls in one region or another.
Wind load is not as harmless as it might seem at first glance. In some cases, we have to talk about the load due to the weight of one of the hip elements. Most often, the sheathing or roofing acts as a weighting agent.
The issue of load appears relevant to those who is going to use the attic space year-round. In this case, large-scale insulation is necessary (slopes, side walls, etc.), which leads to a significant increase in the force of pressure on the surface of the walls. When they do not plan to convert the attic into a living space, then only the ceiling needs to be insulated.
The supporting structure of the eaves can also exert a noticeable load with its own weight. In this situation, load indicators are determined taking into account the average density of materials and the design values of structural and geometric parameters.
All of the above influencing factors are not so easy to analyze, but fortunately, all the necessary SNiPs have long been developed, the standards of which can be referred to at any time.
Coverage area calculation
Inevitable in any canopy design. If the surface of the house will be displayed in a single-pitched plane, then you are very lucky with the calculations.
In such conditions, measure the length and width of the structure, add up the indicators of conditional overhangs and then multiply the two results by one another.
When it comes to the roof, then several more positions should be used in the calculation, including the angle of inclination of one or another element. First of all, we recommend dividing all capacious parts of the coating into certain parts (for example, into triangles).
In the case of a gable surface, you should multiply the area of each slope separately by the cosine of the inclined angle. The inclined angle is a figure taken from the intersection of the slope and the ceiling. As for measuring the length of one inclined slope, the mentioned parameter should be fixed at the existing distance from the ridge to the edge of the cornice.
Calculation of roof area
Consequently, the solution algorithm in all projects that use pitched eaves is similar. Upon completion of the above steps, in order to find out the area of the house dome, you will need to sum up the results obtained.
Construction warehouses and related stores may sell slopes with the shape of an irregular polygon. In this case, remember the advice that was already sounded in the material - divide the plane into equal geometric figures and after completing the calculations, simply add them together.
Calculation of the amount of roofing materials using metal tiles as an example
Metal tiles should begin to be considered from the angle of inclination, which was already mentioned in the previous paragraph. If we talk about extremes, then there is every theoretical reason to say about the interval 11-70 degrees. But practice, as we know, makes its own adjustments and they do not always coincide with theory.
Experts say that 45 degrees is the optimal tilt angle.
Moreover, if we are talking about the roof of a house, which is located in an area with minimal rainfall, which does not require significant slopes. If snow is a fairly frequent visitor, then 45 degrees will be the most optimal options, but due to the increase in wind pressure, it will be necessary to strengthen the sheathing and rafter system. In addition, the greater the slope, the more material will go to the eaves.
Let's consider the calculation algorithm using the example of a gable roof:
- Let the inclined angle be expressed by the letter A, and ½ of the covered span will be B, the height will be H.
- We introduce the action of finding the tangent, which is solved by dividing H by B. We know the mentioned values, therefore, using the Bradis table, we find the value of the angle of inclination A through the arctangent (H/B).
- To solve such serious actions, it is better to use a calculator capable of calculating inverse trigonometric functions. Then multiply B by the length of the covering to find the area of each slope.
Regarding material costs, such calculations are addressed already at the final design stage. First, you need to calculate the surface area that will be laid and the actual dimensions of the roofing material. Let's take metal tiles as an example.
Roof area
So, the real width parameter is 1180 mm, the effective width is 1100 mm. Now we move on to calculating the length of the house covering, which we have already talked about. Since we are analyzing a fictitious calculation as an example, let the mentioned indicator be equal to 6 meters.
We divide this number by the effective width and get 5.45. The action solution displays the quantity the necessary sheets and since the number was not a whole number, for obvious reasons we rounded up.
Thus, we will need 6 sheets of metal tiles to lay one row along the length of the eaves. Let's move on to calculating the number of sheets vertically.
To measure the vertical row, you should take into account the size of the overlap (usually taken as 140-150 mm), the distance between the ridge and the eaves, as well as the length of the eaves overhang.
Let the distance be 4 meters, and the overhang - 30 cm. Having made a simple addition, we get a size of 4.3 meters. Let's take the conventional length of a metal tile sheet as 1 meter. Taking into account the overlap, the effective length of one roofing unit will be 0.85 m.
After this, divide the result of 4.3 m by effective length and at the end we get 5.05 sheets. In such a small deviation from the whole number, we recommend rounding down.
Calculation of vapor and waterproofing
- and it is considered very simple. To do this, you simply need to divide the covered area by a similar parameter of the roofing. For example, we are talking about a gable canopy.
Conventionally, we take the length of the slope to be 5 meters and the width to be 4 m. Therefore, the area of one unit is 20 square meters. m, and the total figure for two slopes will be 40 sq. m. Steam and waterproofing material It is customary to count by rolls.
Useful video
Video instructions for roof calculations:
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