The gable roof rafter system is a fairly simple design and is available for DIY construction even for home builders. It is only necessary to first make a calculation of the gable roof rafter system, get acquainted with the stages and methods of its construction, calculate the required materials for installation. During the calculations, it is necessary to take into account that the bearing capacity of a gable roof will depend on the effect of loads on it from the weight of materials, snow, wind.

To make the process of installing the rafters of a gable roof with your own hands as simple as possible, the step-by-step and detailed installation instructions are described below.

Basic requirements for materials

To install the rafter system, the best option is selection of softwood lumber- larch, spruce or pine, I - III grade.

It is made of timber or boards of the II grade, for the rafters the material is used not lower than the II grade, the lathing is made of lumber of the II-III grade, the material of the II grade is used for the purlins and racks, this will depend on the characteristics of the roof. Grade III material can be used for linings and onlays. Tightens and crossbars are made of grade I material.

Lumber must be stored under a canopy providing protection from moisture and sun. For storage, the site must be leveled; for ventilation, shift the lumber with linings.

For the construction of the gable roof truss system, fasteners will be required: plates, ties, bolts with nuts and washers, studs, mounting tape, self-tapping screws with EPDM gaskets with a thickness of 2.9 mm, galvanized brackets.

Brackets are used to mount the Mauerlat, they are fastened with screws or nails. KR corners prevent the rafters from displacing and are necessary for fastening to the rafter Mauerlat. All material for fasteners must be protected against corrosion and be made of quality material.

Instruments

For installing a gable roof rafter system such a set of tools will be needed:

For safety reasons, all tools on the roof must be kept in a special bag.

Varieties for gable roof rafter systems

Send rafter system

It rests on racks and a Mauerlat, which are installed on the inner wall, with an equal pitch of the rafters. Additionally, to impart rigidity, set struts with spans over 6 m.

Hanging rafters

If the house is small in width, then it is possible to install rafter systems when they rest on walls or a Mauerlat without intermediate supports. The maximum width is 10 meters. In some cases, these roofs can be installed without a Mauerlat. The rafter system is installed on the wall using spacers; in this version, a bending moment acts on the rafters.

In order to unload, set metal or wooden lining... They fix the angle firmly. For a hanging rafter system of a larger span, struts and a headstock are installed. The rafter for hanging systems is set with a larger section, and lumber is chosen not lower than grade III.

Calculation of the rafter system

An approximate calculation of the load from wind and snow is made according to the table values ​​of SNiP taking into account the temperature zone and the height of the building. The load from the snow is equal to its weight, multiplied by a factor that depends on the slope of the slope. All these calculations are made during design.

And if you are installing a gable roof truss system for a small building, and there is no project? You need to look at the construction of the same building in the neighborhood, made according to the project, the roof area is the same as yours. The gable roof rafter system will be used as a reference.

You can also use the online gable roof calculator, it can help you calculate the maximum roof load, the required amount of battens, the rafters slope angles, as well as the materials that will be required to build this type of roof at a given size. On the calculator, you can calculate the roof from such commonly used materials as ondulin, slate, metal tiles, bituminous, cement-sand and ceramic tiles, and other roofing materials.

Sizes of timber for rafters

The ridge fits at the top point, it is necessary to connect the rafters. The height of the ridge will depend on the slope of the roof. The choice of coating material affects the slope. The minimum slope is as follows:

The optimal tilt angle of 30-40 degrees creates a quick discharge of snow and water. In areas with strong winds, the roof is made flat, and in this case the slope angle is in the range of 25-40 degrees.

The roof does not end at the level of the walls, it must be extended outward by 50 cm. In this case, water does not flood the foundation and does not fall on the wall.

Step-by-step installation of the structure of the gable roof rafter system

The gable roof rafter system consists of the following elements:

Mauerlat installation

Mauerlat evenly distributes the load on the walls of the house, its installation is carried out in several ways:

• common and simple option for ordinary roofs, wire rod fastening;
• studs are installed in the masonry;
• to be attached to the wall through a reinforced concrete belt with studs.

What is used for a beam with a section of 10 × 10 cm, 15 × 15 cm or 20 × 20 cm. Which section to select will depend on the roof covering and its dimensions. The Mauerlat is joined along the length, for which you need to make a wash down with a length of 50 cm, 10 cm each, lay the bars and fix with pins.

Mauerlat in the corners is tied in half a bar with cuts, fixed with bolts or brackets. Mauerlat at wooden structures is the last crown. On the brick walls, you need to make a reinforced monolithic reinforced concrete belt, 40 × 30 cm in size.Install pins with threads 12 mm in diameter along the belt for fastening, every 1.2 cm.

In the Mauerlat for a gable roof, it is necessary drill 12 mm holes, lay it down so that the pins enter the holes. Tighten with nuts from above. We pre-lay several layers of roofing roofing or roofing material under the block. On the outside of the wall, you need to lay the Mauerlat brick. The Mauerlat is laid on an even base, vertically and horizontally. It is necessary to check the diagonals and the level to determine the horizontalness of the surface. If necessary, align with shims.

Installation instructions for racks, beds, braces, struts and rafters of a gable roof

Do-it-yourself installation of a gable roof rafter system produced in this order:

The rafter legs are connected to each other on a skate... Let's describe the most common joints of the rafter system:

• Cuts are made near one leg and washed down near the other. Install one leg in the cut with the other and fix it with a bolt.
• The linings are installed metal or wooden.
• The girder is fastened with bolts or nails with the help of notches.

Do-it-yourself installation of the lathing

The lathing is arranged along the roof rafters. It is required to distribute the load from snow and roofing material to the rafters, and also serves as an air gap between the rafter system and the roof.

The design of the battens will depend on the roofing material used:

Pine of the first grade is usually chosen as lumber for the manufacture of lathing. It is recommended to take the width no more than 15 cm. With a larger width, the boards can deform and damage the roofing. The length of the nails should be 3 times the thickness of the sheathing. Boards are laid along the ridge.

A continuous crate is made along the roof slope... The first layer is laid by the board along the ridge, from it with a step of 50-100 cm the next one and then everything is repeated. The next layer is to lay the crate along the rafters. The joints between the boards are made at a distance and only on the rafters. The nail is completely sunk into the wood with the head.

Eaves overhangs

Eaves overhangs need to be made to protect from atmospheric precipitation, these elements fulfill an aesthetic role. They must be installed tightly without gaps. This is the final stage in the arrangement of the gable roof.

Gable

The gable roof has two gables, which look in the shape of a triangle, with the apex near the ridge, while the sides should coincide with the slopes of the roof. The gables enclose the attic space and support the rafters, stabilize the roof and protect it from rain and wind.

In wooden structures, the pediment is made frame. In brick structures, brick or frame. Gables made of aerated concrete or brick are made before the roof device and at the same time require a fairly precise execution. Frame gables are installed in the prepared opening when the rafter system has already been assembled.

The frame is made from boards or bars... All parts of the frame are connected to the floor of a tree or on thorns, everything is fixed with nails. Sheathed by nailing siding, lining or boards, observing the colorist in finishing the facade of the house. To equip the window opening, an additional frame must be made in size for it. When the attic is insulated, the pediment must also be insulated. The insulation must be laid in the middle of the frame. Insulation is used mineral wool with low flammability. From the outside, the frame is upholstered with a windproof membrane or a hydro-windproof film, a vapor-proof membrane or a vapor-proof film is nailed under the finishing material from the inside.

Summarizing

As you can see, despite the apparent simplicity and lightness, the plan of the rafters of the gable roof contains many different pitfalls. However, relying on the above recommendations and installation methods, you can easily build a reliable structure with your own hands.

Designing and competent calculations of the elements of the rafter structure is the key to success in the construction and subsequent operation of the roof. She is obliged to staunchly resist the combination of temporary and permanent loads, while at the same time making the building heavier to a minimum.

For the production of calculations, you can use one of the many programs laid out on the network, or do everything manually. However, in both cases, you need to clearly know how to calculate the rafters for the roof in order to thoroughly prepare for construction.

The rafter system determines the configuration and strength characteristics of the pitched roof, which performs a number of significant functions. It is a responsible enclosing structure and an important component of the architectural ensemble. Therefore, in the design and calculations of rafter legs, flaws should be avoided and try to eliminate shortcomings.

As a rule, in design development, several options are considered, from which the optimal solution is selected. Choosing the best option does not at all mean that you need to draw up a certain number of projects, perform accurate calculations for each and, in the end, prefer the only one.

The very course of determining the length, mounting slope, section of the rafters consists in scrupulous selection of the shape of the structure and the size of the material for its construction.

For example, in the formula for calculating the bearing capacity of a rafter leg, the parameters of the section of the most suitable material for the price are initially entered. And if the result does not meet technical standards, then the size of the lumber is increased or decreased until they achieve maximum compliance.

Slope search method

Determining the slope angle of a pitched structure has architectural and technical aspects. In addition to the proportional configuration, the most suitable for the style of the building, an impeccable solution must take into account:

• Snow load indicators. In areas with abundant precipitation, roofs are erected with a slope of 45 degrees or more. Snow deposits do not linger on slopes of such steepness, due to which the total load on the roof is noticeably reduced, and the building as a whole is stalled.
• Wind load characteristics. In areas with gusty strong winds, coastal, steppe and mountainous areas, streamlined low-slope structures are erected. The steepness of the slopes there usually does not exceed 30º. In addition, the winds prevent the formation of snow deposits on the roofs.
• Weight and type of roofing. The more weight and finer the elements of the roof, the steeper you need to build the truss frame. This is necessary in order to reduce the likelihood of leaks through the joints and to reduce the specific gravity of the coating per unit of the horizontal projection of the roof.

In order to choose the optimal angle of inclination of the rafters, the project must take into account all the listed requirements. The steepness of the future roof must correspond to the climatic conditions of the area selected for construction and the technical data of the roofing.

True, property owners in the northern calm areas should remember that with an increase in the angle of inclination of the rafter legs, the consumption of materials increases. Building and equipping a roof with a steepness of 60 - 65º will cost approximately one and a half times more than erecting a structure with an angle of 45º.

In areas with frequent and strong winds, do not cut the slope too much in order to save money. Excessively sloping roofs lose in architectural terms and do not always contribute to lower costs. In such cases, reinforcement of the insulating layers is most often required, which, contrary to the expectations of the economist, leads to an increase in the cost of construction.

The slope of the rafters is expressed in degrees, as a percentage, or in dimensionless units, reflecting the ratio of half the span of the span to the installation height of the ridge girder. It is clear that the degrees delineate the angle between the line of the ceiling and the slope line. Percentages are rarely used because of the complexity of their perception.

The most common method of designating the angle of inclination of rafter legs, used by both designers of low-rise buildings and builders, is dimensionless units. They represent the ratio of the length of the span to be covered to the height of the roof in shares. At the facility, it is easiest to find the center of the future gable wall and install a vertical rail in it with a ridge height mark than to postpone corners from the edge of the slope.

Calculation of the length of the rafter leg

The length of the rafters is determined after the angle of inclination of the system has been selected. Both of these values ​​cannot be attributed to the number of exact values, since in the process of calculating the load, both the steepness and following it, the length of the rafter leg may change somewhat.

The main parameters affecting the calculation of the length of the rafters include the type of eaves overhang, according to which:

1. The outer edge of the rafter legs is trimmed flush with the outer surface of the wall. The rafters in this situation do not form a cornice overhang that protects the structure from precipitation. To protect the walls, a drain is installed, fixed on a cornice board nailed to the end edge of the rafters.
2. The rafters, cut flush with the wall, are built up by fillets to form a cornice overhang. The filly is fastened to the rafters with nails after the construction of the rafter frame.
3. The rafters are initially cut taking into account the length of the eaves. In the lower segment of the rafter legs, cuttings are chosen in the form of an angle. To form the cuts, they retreat from the lower edge of the rafters to the width of the eaves. The cuts are needed to increase the support area of ​​the rafter legs and for the device of support nodes.

At the stage of calculating the length of the rafter legs, it is required to think over the options for attaching the roof frame to the Mauerlat, to the bypasses or to the upper crown of the log house. If you plan to install the rafters flush with the outer contour of the house, then the calculation is carried out along the length of the upper edge of the rafter, taking into account the size of the tooth, if it is used to form the lower connecting node.

If the rafter legs are cut taking into account the eaves, then the length is calculated along the upper edge of the rafters together with the overhang. Note that the use of triangular cuts significantly accelerates the pace of construction of the rafter frame, but weakens the elements of the system. Therefore, when calculating the bearing capacity of rafters with a selected angle of cuttings, a coefficient of 0.8 is used.

The traditional 55 cm is recognized as the average statistical width of the cornice removal. However, the spread can be from 10 to 70 and more. The calculations use the projection of the eaves on the horizontal plane.

There is a dependence on the strength characteristics of the material, on the basis of which the manufacturer recommends limit values. For example, slate manufacturers advise against extending the roof beyond the wall contour for a distance of more than 10 cm, so that the snow mass accumulating along the eaves cannot damage the edge of the cornice.

It is not customary to equip steep roofs with wide overhangs, regardless of the material, the cornices are not made wider than 35 - 45 cm. But structures with a slope of up to 30º can perfectly complement a wide cornice, which will serve as a kind of canopy in areas with excessive sunlight. In the case of designing roofs with eaves of 70 cm or more, they are reinforced with additional support posts.

How to calculate the bearing capacity

In the construction of truss frames, lumber made of coniferous wood is used. The harvested timber or board must not be lower than the second grade.

The rafter legs of pitched roofs work on the principle of compressed, curved and compressed-curved elements. The second-class wood copes with the tasks of resistance to compression and bending excellently. Only if the structural element will work in tension is the first grade required.

Rafter systems are arranged from a board or a bar, they are selected with a margin of safety, focusing on the standard dimensions of the lumber produced in-line.

Calculations of the bearing capacity of rafter legs are carried out in two states, these are:

• Estimated. A condition in which a structure collapses as a result of an applied load. Calculations are carried out for the total load, which includes the weight of the roofing cake, the wind load, taking into account the number of storeys of the building, the mass of snow, taking into account the slope of the roof.
• Normative. A condition in which the rafter system bends, but the destruction of the system does not occur. It is usually impossible to operate the roof in this state, but after carrying out repair operations, it is quite suitable for further use.

In a simplified design, the second state is 70% of the first value. Those. to obtain the standard indicators, the calculated values ​​must be corny multiplied by a factor of 0.7.

The loads, depending on the climatic data of the construction region, are determined according to the maps attached to SP 20.13330.2011. The search for standard values ​​on maps is extremely simple - you need to find the place where your city, cottage village or other nearest settlement is located, and take readings about the calculated and standard value from the map.

The average information about snow and wind loads should be adjusted according to the architectural specifics of the house. For example, the value taken from the map must be distributed along the slopes in accordance with the wind rose compiled for the area. You can get a printout from your local weather service.

On the windward side of the building, the mass of snow will be much less, therefore, the calculated indicator is multiplied by 0.75. On the leeward side, snow deposits will accumulate, so multiply here by 1.25. Most often, in order to unify the material for building a roof, the leeward part of the structure is constructed from a paired board, and the windward part is arranged with the rafters of their single board.

If it is not clear which of the slopes will be on the leeward side, and which is the opposite, then it is better to multiply both by 1.25. The safety margin does not hurt at all, if it does not increase the cost of lumber too much.

The calculated snow weight indicated by the map is also adjusted depending on the steepness of the roof. From the slopes set at an angle of 60º, the snow will immediately slide off without the slightest delay. In the calculations for such steep roofs, the correction factor is not applied. However, with a lower slope, snow can already be trapped, therefore, for slopes of 50º, an additive is used in the form of a coefficient of 0.33, and for 40º it is the same, but already 0.66.

The wind load is determined in the same way according to the corresponding map. The value is adjusted depending on the climatic specifics of the area and on the height of the house.

To calculate the bearing capacity of the main elements of the projected rafter system, it is required to find the maximum load on them, summing up the temporary and constant values. No one will strengthen the roofs before the snowy winter, although in the country it would be better to put safety vertical struts in the attic.

In addition to the mass of snow and the pressing force of the winds in the calculations, it is necessary to take into account the weight of all elements of the roofing pie: the sheathing installed on top of the rafters, the roof itself, insulation, inner lining, if used. The weight of vapor and waterproofing films with membranes is usually neglected.

Information on the weight of materials is indicated by the manufacturer in the technical data sheets. The data on the mass of the bar and the board are taken in approximation. Although the mass of the lathing per meter of projection can be calculated based on the fact that a cubic meter of sawn timber weighs on average 500 - 550 kg / m 3, and a similar volume of OSB or plywood from 600 to 650 kg / m 3.

The load values ​​given in SNiPs are indicated in kg / m 2. However, the rafters perceive and hold only the load that directly presses on this linear element. In order to calculate the load on the rafters, the set of natural tabular values ​​of the loads and the mass of the roofing cake is multiplied by the step of installing the rafter legs.

The load value reduced to linear parameters can be reduced or increased by changing the step - the distance between the rafters. By adjusting the load collection area, its optimal values ​​are achieved in the name of the long service life of the pitched roof frame.

Determination of the cross-section of the rafters

The rafter legs of roofs of various steepness perform an ambiguous job. The bending moment acts mainly on the rafters of shallow structures; on the analogs of steep systems, a compressive force is added to it. Therefore, in the calculations of the cross-section of the rafters, the slope of the slopes must be taken into account.

Calculations for structures with a slope up to 30º

Only bending stress acts on the rafter legs of the roofs of the specified steepness. They are calculated for the maximum bending moment with the application of all types of load. Moreover, temporary, i.e. climatic loads are used in calculations based on maximum values.

For rafters that have only supports under both their own edges, the point of maximum bend will be in the very center of the rafter leg. If the rafter is laid on three supports and is composed of two simple beams, then the moments of maximum bending will fall in the middle of both spans.

With a solid rafter on three supports, the maximum bend will be in the area of ​​the central support, but since there is a support under the bending section, then it will be directed upward, and not, as in the previous cases, downward.

For normal operation of the rafter legs in the system, two rules must be followed:

• The internal stress formed in the rafter during bending as a result of the load applied to it must be less than the calculated value of the bending resistance of the sawn timber.
• The deflection of the rafter leg must be less than the normalized deflection value, which is determined by the ratio L / 200, i.e. the element is allowed to bend only by one two hundredth of its real length.

Further calculations consist in the sequential selection of the dimensions of the rafter leg, which, as a result, will satisfy the specified conditions. There are two formulas for calculating the cross section. One of them is used to determine the height of a board or timber by an arbitrary specified thickness. The second formula is used to calculate the thickness at an arbitrary height.

In calculations, it is not necessary to use both formulas, it is enough to apply only one. The result obtained as a result of the calculations is checked according to the first and second limiting states. If the calculated value turned out with an impressive margin of safety, an arbitrary indicator entered into the formula can be reduced so as not to overpay for the material.

If the calculated value of the bending moment is greater than L / 200, then the arbitrary value is increased. The selection is carried out in accordance with the standard dimensions of the commercially available sawn timber. This is how the section is selected until the moment when the optimal version is calculated and obtained.

Let's consider a simple example of calculations using the formula b = 6Wh². Suppose h = 15 cm, and W is the ratio M / R out. We calculate the M value using the formula g × L 2/8, where g is the total load vertically directed to the rafter leg, and L is the span length equal to 4 m.

R iz for sawn softwood is taken in accordance with technical standards 130 kg / cm 2. Suppose we calculated the total load in advance, and we got it equal to 345 kg / m. Then:

M = 345 kg / m × 16m 2/8 = 690 kg / m

To convert to kg / cm, divide the result by 100, we get 0.690 kg / cm.

W = 0.690 kg / cm / 130 kg / cm 2 = 0.00531 cm

B = 6 x 0.00531 cm x 15 2 cm = 7.16 cm

We round the result as it should be in the big direction and we find that for the device of rafters, taking into account the load given in the example, a beam of 150 × 75 mm is required.

We check the result for both states and make sure that the material with the cross section calculated now is suitable for us. σ = 0.0036; f = 1.39

For roof systems with a slope over 30º

The rafters of roofs with a steepness of more than 30º are forced to resist not only bending, but also the force compressing them along their own axis. In this case, in addition to checking the bending resistance described above and by the amount of bending, it is necessary to calculate the rafters by internal stress.

Those. actions are performed in a similar order, but there are slightly more verification calculations. In the same way, an arbitrary height or arbitrary thickness of the lumber is set, with its help the second parameter of the section is calculated, and then a check is carried out for compliance with the above three technical conditions, including the compression resistance.

If it is necessary to increase the bearing capacity of the rafters, the arbitrary values ​​entered into the formulas are increased. If the safety margin is large enough and the standard deflection significantly exceeds the calculated value, then it makes sense to perform the calculations again by reducing the height or thickness of the material.

To select the initial data for the production of calculations, a table will help, which summarizes the generally accepted sizes of lumber we produce. It will help you choose the section and length of the rafter legs for initial calculations.

Video about the calculations of rafters

The video clearly demonstrates the principle of performing calculations for the elements of the rafter system:

Calculating the load-bearing capacity and rafter angle is an important part of the roof frame design. The process is not easy, but it is necessary to understand it both for those who make calculations manually and for those who use the calculation program. You need to know where to get tabular values ​​and what the calculated values ​​give.

Online roof and roof calculators are must-have tools in the arsenal of architects and professional construction firms. Although, in principle, such calculators are also useful for ordinary owners of suburban areas who have started building a house with their own hands (here you will also need to calculate the roof). And it is not surprising, because the quality and accuracy of such calculations directly affect not only the durability of the entire roof structure, but also the general appearance of the house. This section of the site contains the best calculators for calculating the roof, which will help you in the most common cases when building a house yourself! Here you will find useful tools for calculating the area of ​​a three-gable roof, the amount of slate, the area of ​​the hipped roof, the length of the rafter legs, the height of the ridge and much more! All online calculators have been created by experienced professionals, each tool is accompanied by detailed explanations and instructions for calculating.

What are the advantages of our online calculators? They differ from their numerous (and often paid) counterparts in that they do not need to be downloaded to a local computer. Complex, thoroughly tested algorithms are used to carry out calculations, and the results of calculations are displayed in a simple and accessible form. Another advantage is that you can add a page with an interesting online calculator to your browser bookmarks and use it at any time!

On a note! When making calculations online, building standards, GOSTs and SNiPs, which are adopted in the Russian Federation and the world, are used. In addition, the world practice of modern construction is taken into account.

Metal tiles have appeared in a series of roofing materials relatively recently, but quickly gained popularity. This can be explained simply - with proper installation, such a cover provides reliable protection of the house from atmospheric precipitation, while at the same time giving the roof a reliable imitation of natural classic tiles.

The popularity of this coating is also based on the fact that its installation is not difficult, and the owner of the house must cope with it even on his own, of course, having an assistant, but without resorting to hiring a team. The clear profile of the metal tile allows you to easily combine neighboring sheets, and it is very difficult to make a mistake even if you wish. But all this will be true only if a high-quality lathing is mounted under such a roof. To figure out how many boards or beams will be required to create it, a calculator for calculating lumber for lathing under metal tiles will help.

Below will be a few comments about working with the program.

Before starting the calculations, you need to understand that the roof and the roof are not identical concepts. By "roof" we mean the entire system that stands on the Mauerlat: rafters, lathing and counter-battens, all kinds of insulation and, finally, roofing material, that is, the "roof" itself. The online roof calculator with drawings allows you to get data on both the roof and the roof - in a format convenient for you.

The finished calculation of the rafter system and metal tiles for the roof (as well as other types of roofing) can be saved both in the form of simple numbers for the number of building materials, and in the form of drawings and 3D models. You can save the result on a PC or mobile device from which you entered the data, as well as send it by e-mail to yourself or to the specialist who was engaged in the design of your facility. By the way, it is recommended to consult with him or with a professional estimator before purchasing: the online calculator for calculating the roof with roof drawings is designed for standard initial data - your object may have features that the service will not take into account.

Using the service, you can make calculations:

• shed, gable, hipped roof, including hip roof;
• any of the listed types of roofs, taking into account the attic;
• any of the listed types of roofs, taking into account the different angle of inclination;
• roof area.

All data is entered in centimeters - for example, the length of the roof along the ridge, which will be 12 meters, must be indicated as 12,000 centimeters; The service also gives results in centimeters.

If necessary, you can tick the boxes under the main data to take into account additional materials: Mauerlat, counter-lattice, waterproofing and insulation. The service takes into account the most used types and grades of materials.