Hip roofs are used both for low-rise residential buildings and for various outbuildings. Most often they are built over buildings that have equilateral bearing walls, and the foundation plan is of a square type. You can also find such architectural elements above round structures, in which case the number of slopes is more than four.
The main difference between a hipped roof is the complete absence of a ridge. This is a very important part of the truss systems, it takes on the efforts of the rafter legs. The function of this element is assigned to the central support, at the top of which the rafters converge. In this regard, great attention should be paid to its strength. There are options for truss systems without a central support, the upper heels of the rafter legs rest against each other. Such options are most often used on small buildings. All slopes of the tent system are in the form of equilateral triangles.
A hipped roof has many manufacturing options, but everyone must have the following elements.
Types of truss systems, advantages and disadvantages of a hipped roof
Table. The main types of tent truss system.
Benefits of a hipped truss system
The disadvantages include the complexity in the manufacture of the truss system. The hipped roof has a large number of various nodes and elements, each of which can have a negative impact on stability indicators. Another disadvantage is the difficulty in retrofitting attic space for residential, such options for truss systems are extremely rarely used for attics. Sometimes the disadvantages include increased consumption of roofing materials, but this depends not so much on the features of the rafter system, but on the professionalism of the roofers.
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General tips for building hipped roof truss systems
Specific decisions are made by the master, taking into account the dimensions and design features of the hipped roof. But for all cases, there are general recommendations, the implementation of which guarantees the stability of the structure.
Additional stops for slanting rafters
The top of the tent system
Very complex from a technological point of view and the most responsible node from an architectural point of view. It has two solutions: rafter legs rest on one support installed in the center of the building, or against each other. The first option provides maximum structural stability, but its installation requires a rigid support. The best option - in the middle of the building there is a load-bearing wall. An acceptable option - during the construction of the ceiling, reinforced beams or lie down. When calculating the parameters, the maximum possible roof loads must be taken into account and a safety factor applied.
The use of the connection only in the upper heels of the rafters without vertical support is used only on small structures. At the same time, a complex of special construction measures is used to increase the rigidity of the structure.
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They can be fixed using special bottom stops, directly to the rafters or in a mixed way. Modern technologies allow you to fix the sprigs without cutting, which not only strengthens the truss system, but also greatly simplifies the work.
The design solutions of a hipped roof, especially without a central support, significantly increase the expansion loads on the mauerlat. This situation requires its strengthening, all nodes must be built according to accurate calculations and with unconditional observance of building codes.
And finally, a general recommendation - if you do not have a serious practical experience construction of ordinary pitched truss systems, then it is absolutely not worth taking on a tent. This is one of the most complex truss systems, all its elements are so interconnected and interdependent that the violation of the stability of one becomes the cause of the complete destruction of the roof. The tent truss structure does not have completely identical elements; everyone needs to be approached individually.
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Calculation of the tent structure
First, consider the algorithm for calculating the main values of the system. We take into account that the roof has four slopes, each of which is an equilateral triangle. The angle of inclination of the slopes is selected depending on the coverage area and climate zone location of the object. Taking into account the climatic zone in the tables of building codes and rules, the minimum allowable angle of inclination of the slopes is selected.
The length of the central rafter depends on the angle of inclination and is determined by the well-known formula of a right triangle. First you need to find the length of the diagonal, this is done by calculation or by ordinary measurement. The second method is easier, use a tape measure to find this value.
We have an angle of inclination of the slopes, find the tangent on the Internet, multiply it by the length of half of the leg and the result will be the height of the vertical support of the hipped roof. Next, you should calculate the length of the rafter. It is calculated using several formulas, the simplest of which is the Pythagorean theorem: c2=a2+b2, where:
c - the length of the rafter;
a - half of the leg of the structure;
b is the height of the vertical support.
Hence - the length of the rafter is equal to the square root of the sum of the squares of the indicated values. That's all, if it's difficult to do it yourself, then there are a large number of online calculators on the Internet. After entering the data, not only the dimensions of the system elements are given, but also their number is calculated.
Rafters perform a number of significant roofing functions. They set the configuration of the future roof, perceive atmospheric loads, and hold the material. Among the rafter duties, the formation of even planes for laying the coating and providing space for the components roofing cake.
In order for such a valuable part of the roof to flawlessly cope with the listed tasks, information about the rules and principles of its construction is needed. The information is useful both for those who are building a gable roof truss system with their own hands, and for those who decide to resort to the services of a hired team of builders.
In the device of the truss frame for pitched roofs using wooden and metal beams. The starting material for the first option is a board, log, timber.
The second is constructed from rolled metal: a channel, a profile pipe, an I-beam, a corner. There is combined designs with steel most loaded parts and wood elements in less critical areas.
In addition to the "iron" strength, the metal has a lot of disadvantages. These include heat engineering qualities that do not satisfy the owners of residential buildings. Disappointing need for the use of welded joints. Most often, industrial buildings are equipped with steel rafters, less often private change houses assembled from metal modules.
In the case of independent construction roof structures for private houses, wood is a priority. It is easy to work with it, it is lighter, “warmer”, more attractive in terms of environmental criteria. In addition, nodal connections do not require welding machine and welding skills.
Rafters - a fundamental element
The main "player" of the frame for the construction of the roof is the rafter, among the roofers called the rafter leg. Beds, braces, headstocks, girders, puffs, even Mauerlat may or may not be used depending on the architectural complexity and dimensions of the roof.
The rafters used in the construction of the gable roof frame are divided into:
- Layered rafter legs, both heels of which have reliable structural supports under them. The lower edge of the layered rafter rests on the Mauerlat or on the ceiling crown of the log house. The support for the upper edge can be a mirror analogue of the adjacent rafter or a run, which is a beam horizontally laid under the ridge. In the first case, the truss system is called spacer, in the second, non-spacer.
- hanging rafters, the top of which rests against each other, and the bottom is based on an additional beam - puff. The latter connects the two lower heels of adjacent rafter legs, resulting in a triangular module called a truss truss. The tightening dampens the tensile processes, so that only a vertically directed load acts on the walls. The design with hanging rafters, although it is spacer, does not transfer the spacer itself to the walls.
In accordance with the technological specifics of the rafter legs, the structures constructed from them are divided into layered and hanging. For structural stability, they are equipped with struts and additional racks.
For the arrangement of supports for the top of the layered rafters, beds and girders are mounted. In reality, the truss structure is much more complicated than the elementary patterns described.
Note that the formation of a gable roof frame can generally be carried out without a truss structure. In such situations, the alleged planes of the slopes are formed by slegs - beams laid directly on the bearing gables.
However, we are now specifically interested in the device of the truss system gable roof, and it can involve either hanging or layered rafters, or a combination of both types.
Subtleties of fastening rafter legs
The truss system is fastened to brick, foam concrete, aerated concrete walls through the mauerlat, which in turn is fixed with anchors.
Between the Mauerlat, which is a wooden frame, and the walls of these materials, a waterproofing layer of roofing material, waterproofing, etc. is necessarily laid.
The top of the brick walls is sometimes specially laid out so that something like a low parapet is obtained along the outer perimeter. So it is necessary that the Mauerlat placed inside the parapet and the walls do not burst the rafter legs.
Roof frame rafters wooden houses rest on the upper crown or on ceiling beams. The connection in all cases is made by cutting and duplicated with nails, bolts, metal or wooden plates.
How to do without furious calculations?
It is highly desirable that the cross section and linear dimensions of the wooden beams be determined by the project. The designer will give clear calculation justifications for the geometric parameters of the board or beam, taking into account the entire range of loads and weather conditions. If available home master there is no design development, his path lies on the construction site of a house with a similar roof structure.
You can ignore the number of storeys of the building under construction. It is easier and more correct to find out the required dimensions from the foreman than to find them out from the owners of a shaky unauthorized construction. After all, the foreman is in the hands of documentation with a clear calculation of the loads per 1 m² of roof in a particular region.
The installation step of the rafters determines the type and weight of the roofing. The heavier it is, the smaller the distance between the rafter legs should be. For styling clay tiles, for example, the optimal distance between the rafters will be 0.6-0.7 m, and for the profiled sheet and 1.5-2.0 m is acceptable.
However, even if the step required for the correct installation of the roof is exceeded, there is a way out. This is a reinforcing counter-lattice device. True, it will increase both the weight of the roof and the construction budget. Therefore, it is better to deal with the step of the rafters before the construction of the rafter system.
Craftsmen calculate the pitch of the rafters according to the design features of the building, tritely dividing the length of the ramp into equal distances. For insulated roofs, the step between the rafters is selected based on the width of the thermal insulation boards.
On our website you can find, which may also help you a lot during construction.
Rafter structures of layered type
Rafter structures of the layered type are much simpler in execution than their hanging counterparts. A justified plus of the layered scheme is to provide full ventilation, which is directly related to the longevity of the service.
Distinctive design features:
- Mandatory presence of support under the ridge heel of the rafter leg. The role of the support can be played by a run - a wooden beam resting on racks or on the inner wall of the building, or the upper end of an adjacent rafter.
- The use of Mauerlat for the construction of a truss structure on walls made of brick or artificial stone.
- The use of additional runs and racks where the rafter legs, due to the large size of the roof, require additional support points.
The minus of the scheme is the presence of structural elements that affect the layout of the internal space of the operated attic.
If the attic is cold and organization is not supposed to be in it utility rooms, then the layered design of the truss system for the installation of a gable roof should be preferred.
A typical sequence of work on the construction of a layered truss structure:
- First of all, we measure the height of the building, the diagonals and the horizontalness of the upper cut of the skeleton. When detecting vertical deviations of brick and concrete walls, remove them cement-sand screed. Exceeding the heights of the log house we squeeze. By placing chips under the Mauerlat, vertical flaws can be dealt with if their magnitude is insignificant.
- The floor surface for laying the bed must also be leveled. He, the Mauerlat and the run must be clearly horizontal, but the location of the listed elements in the same plane is not necessary.
- We process everything wooden details structures before installation with flame retardants and antiseptics.
- We lay waterproofing on concrete and brick walls for the installation of a Mauerlat.
- We lay the Mauerlat beam on the walls, measure its diagonals. If necessary, we slightly move the bars and turn the corners, trying to achieve the perfect geometry. Align the frame horizontally if necessary.
- We mount the Mauerlat frame. The splicing of the beams into a single frame is carried out by means of oblique cuts, the joints are duplicated with bolts.
- We fix the position of the Mauerlat. Fasteners are made either with brackets to wooden plugs laid in the wall ahead of time, or with anchor bolts.
- We mark the position of the bed. Its axis should recede from the Mauerlat bars at equal distances on each side. If the run will be based only on racks without lying down, the marking procedure is carried out only for these columns.
- We install the bed on a two-layer waterproofing. We fasten it to the base with anchor bolts, with inner wall connect with wire twists or staples.
- We mark the installation points of the rafter legs.
- We cut out racks according to uniform sizes, because our bed is set to the horizon. The height of the racks must take into account the dimensions of the section of the run and the bed.
- Installing racks. If provided by the project, we fix them with spacers.
- We lay the run on the racks. We check the geometry again, then install the brackets, metal plates, wooden mounting plates.
- We install a trial rafter board, mark the places of trimming on it. If the Mauerlat is set strictly to the horizon, there is no need to adjust the roof rafters in fact. The first board can be used as a template for making the rest.
- We mark the installation points of the rafters. Folk craftsmen for marking usually prepare a pair of slats, the length of which is equal to the gap between the rafters.
- According to the markup, we install the rafter legs and fasten them first at the bottom to the Mauerlat, then at the top to the run to each other. Every second rafter is screwed to the Mauerlat with a wire bundle. AT wooden houses the rafters are screwed to the second crown from the top row.
If the rafter system is done flawlessly, the layered boards are mounted in random order.
If there is no confidence in the ideal structure, then the extreme pairs of rafters are installed first. A control twine or fishing line is stretched between them, according to which the position of the newly installed rafters is adjusted.
The installation of the truss structure is completed by installing the filly, if the length of the rafter legs does not allow the formation of an overhang of the required length. By the way, for wooden buildings, the overhang should “go beyond” the contour of the building by 50 cm. If the organization of the visor is planned, separate mini-rafters are installed under it.
Another useful video about the construction of a gable truss base with your own hands:
Hanging truss systems
The hanging type of truss systems is a triangle. The two upper sides of the triangle are folded by a pair of rafters, and the puff connecting the lower heels serves as the base.
The use of tightening allows you to neutralize the effect of the spread, therefore, only the weight of the crate, the roof, plus, depending on the season, the weight of precipitation, acts on walls with hanging truss structures.
The specifics of hanging truss systems
Characteristic features of hanging type truss structures:
- Mandatory presence of a puff, made most often of wood, less often of metal.
- The ability to refuse the use of Mauerlat. A frame made of timber will be successfully replaced by a board laid on a two-layer waterproofing.
- Installation on the walls of ready-made closed triangles - roof trusses.
To the virtues hanging circuit include space under the roof free from racks, allowing you to organize an attic without pillars and partitions. There are disadvantages.
The first of them is the restrictions on the steepness of the slopes: their slope angle can be at least 1/6 of the span triangular truss, steeper roofs are highly recommended. The second disadvantage is the need for thorough calculations for the competent device of cornice nodes.
Among other things, the angle of the truss truss will have to be set with jewelry accuracy, because. the axes of the connected components of the hanging rafter system must intersect at a point, the projection of which must fall on the central axis of the Mauerlat or the lining board replacing it.
Subtleties of long-span hanging systems
Puff - the longest element of the hanging rafter structure. Over time, it, as is typical of all lumber, deforms and sags under the influence of its own weight.
Owners of houses with spans of 3-5m are not too concerned about this circumstance, but owners of buildings with spans of 6 meters or more should think about installing additional details, excluding geometric changes in tightening.
To prevent sagging in the installation scheme of the truss system for a large-span gable roof, there is a very significant component. This is a pendant called a grandmother.
Most often, it is a bar attached with wooden surfs to the top of the truss truss. You should not confuse the headstock with the racks, because. its lower part should not come into contact with the puff at all. And the installation of racks as supports in hanging systems ah does not apply.
The bottom line is that the headstock, as it were, hangs on a ridge knot, and a tightening is already attached to it with the help of bolts or nailed wooden plates. Threaded or collet type clamps are used to correct slack.
Adjustment of the tightening position can be arranged in the zone of the ridge knot, and the headstock can be rigidly connected to it with a notch. Instead of a bar on non-residential attics reinforcement can be used to make the described tightening element. It is also recommended to arrange a headstock or suspension where the puff is assembled from two bars to support the connection area.
In an improved hanging system of this type, the headstock is complemented by strut beams. The stress forces in the resulting rhombus are extinguished spontaneously due to the competent arrangement of the vector loads acting on the system.
As a result, the truss system pleases with stability with a slight and not too expensive upgrade.
Hanging type for attics
In order to increase the usable space, the tightening of the rafter triangles for the attic is moved closer to the ridge. A perfectly reasonable move has additional advantages: it allows you to use puffs as the basis for filing the ceiling.
It is attached to the rafters by cutting with a semi-frying pan with a duplication of a bolt. It is protected from sagging by installing a short headstock.
A noticeable drawback of the attic hanging structure is the need for accurate calculations. It is too difficult to calculate it on your own, it is better to use a ready-made project.
Which design is more cost effective?
Cost is an important argument for an independent builder. Naturally, the price of construction for both types of truss systems cannot be the same, because:
- In the construction of a layered structure for the manufacture of rafter legs, a board or beam of small section is used. Because layered rafters have two reliable supports under them, the requirements for their power are lower than in the hanging version.
- In the construction of a hanging structure, the rafters are made of thick timber. For the manufacture of puffs, a material similar in cross section is required. Even taking into account the rejection of the Mauerlat, the consumption will be significantly higher.
Saving on the grade of material will not work. For the bearing elements of both systems: rafters, purlins, beds, Mauerlat, attendants, racks, lumber of the 2nd grade is needed.
For crossbars and puffs working in tension, you will need the 1st grade. In the manufacture of less responsible wooden slips, the 3rd grade can be used. Without counting, we can say that in the construction of hanging systems, expensive material is used to a greater extent.
Hanging trusses are assembled in an open area next to the facility, then transported to assembled up. To lift weighty triangular arches from a bar, you will need equipment, for which you will have to pay rent. And the project for complex nodes of the hanging version is also worth something.
Video instruction on the installation of a truss structure of a hanging category:
There are actually many more methods for constructing truss systems for roofs with two slopes.
We have described only the basic varieties that are actually applicable for small country houses and buildings without architectural ideas. However, the information provided is sufficient to cope with the construction of a simple truss structure.
The frame format stands out among a number of types of roofing. It can be done in quite different ways, but in any case, you will need to calculate the rafters and install them according to all the rules. With proper knowledge of the problem, you can solve it on your own without resorting to specialists.
Features and forms of the roof
The frame roof can only be installed with spans no longer than 1220 cm, while the gap from one truss to another is a maximum of 0.6 m. The dimensions of the frame fragments are determined by the span distances and the calculated snow load. Rafters can be either freely installed or accepting loads from attic elements. In the case of a broken roof, it is possible to provide a ceiling height sufficient for a residential attic, and it will look best on a square structure.
The multi-gable roof is considered the most complex and hardly accessible variation for amateur builders. A balanced truss system effectively withstands even very high loads, while having an excellent "appearance". Since the slope is steep, the risk of snow retention will be minimal. But at the same time, all structural elements will have to be calculated very carefully, and a lot of waste will appear in the process. In addition, the valley will have to survive exposure to a significant amount of snow.
Purpose and types of systems
In the most different systems rafters can be used Mauerlat. The mass of the roof of the house varies depending on the area occupied by the slopes and the materials used. But in any case, the load created is very solid. When there is a ridge on the structures, a truss frame must be provided, with legs resting against the walls. Force is applied along several vectors at once, and in the cold season, the accumulation of snow only exacerbates the problem.
Mauerlat is designed to eliminate this shortcoming and prevent the destruction of the walls. This word means a beam of significant section, which can be both wooden and steel. In most cases, they take the same material that was used to form the rafters, but be sure to achieve continuity of the strapping or create strong and especially stable joints. The use of Mauerlat is abandoned only in log houses or in buildings built using frame technology - and even there they have their own parts that perform a similar task. When it is not possible to make a non-breaking block, all fragments must be exactly the same length.
A T-shaped roof is characterized by a tie-in of two wings at a certain angle. Because of this, it is necessary to form a valley. External rafters will rest against support boards. In addition to them, there will also be basic parts that are directly fixed to the wall. In order for everything in the valley to correspond to the task being solved, wooden elements 3.8 cm thick are used. The crate is supposed to be made monolithic, the coating is attached to it with clamps every 50 cm. steel, you can slightly reduce this figure.
A reinforcing belt is often equipped under the Mauerlat. This is especially important if you plan to insulate the roof and provide reliable waterproofing. Such a belt is formed from the same mixture that is used to build the foundation. Completely the entire formwork is poured with concrete in one step, the slightest individual layers are unacceptable. In the aerated concrete wall, intermediate jumpers are cut down at top line blocks - and immediately a practical chute appears. The Mauerlat is attached either with a tie wire, or with reinforcing bolts (but they will not help in any way without a reinforcing belt), or with building studs.
Having dealt with the support for the rafters, you need to find out what they can be, and what is more correct to use to support the roof. Hanging rafters are used if there is no main wall inside the building, their support points are located exclusively on the outer contours.
Such supports were in demand during the construction of:
- residential buildings with one span;
- production facilities;
- various pavilions;
- attic.
This option should not be underestimated, thanks to engineering developments, suspended rafters are able not to bend, covering spans of 15–17 m. But it is important to understand that they gain all their capabilities only in close interaction with other details. You will have to use puffs, and grandmas, and crossbars. The simplest truss is made of two beams connected in the upper position; in configuration, such a device is close to a triangle. Horizontal connection frame parts are provided with a puff (a beam made of wood or a metal profile).
Due to the tightening, the transfer of thrust to the walls is excluded, while the force applied in the horizontal plane is suppressed. External walls survive the action of only those forces whose vector is oriented vertically. Builders do not always place a puff at the very bottom, often it is set at the very ridge. In preparation for the construction of the attic, this element is most often placed higher than the base of the rafter legs. Then it will be possible to make a floor, on the ceiling of which you will not have to beat your head with any careless movement.
Hanging rafters for spans longer than 6 m must be reinforced with hangers and braces. In this case, the monolithic puff is replaced by one assembled from a pair of connected beams. In the classical scheme (triangular hinged), the grassroots bases abut against horizontal parts. For the normal functioning of the system, it is required that the height of the ridge is at least 15% of the span of the trusses. The rafters act on the bend, but tightening does not allow them to move to the sides. In order for the beams to bend less, the ridge knots are cut in with the expectation of eccentricity (the occurrence of a bending force opposite in vector).
Mansard attics are built for the most part with the help of triangular arches on three hinges, and the puffs are assigned the function of floor beams. The components of the tightening are bolted by oblique or direct cutting. Raised tightening can also be used in the construction of rafters under the attic. The higher it rises, the more the ceiling can be raised. But it is important to remember that at the same time, the loads on all elements also increase. The transfer of forces is carried out on the Mauerlat using a movable mount, which dampens changes in size due to changes in humidity and temperature.
The rafters can be subjected to uneven loading, since it is higher on one side. This leads to a shift in the same direction of the entire system. You can eliminate such an unpleasant effect if you take out the rafters beyond the contour of the walls. The tightening with such a decision ceases to be a support, it transfers either tensile effects (if an attic is being arranged), or stretched-bending ones (when an attic is being built). Hinged arches with the inclusion of a crossbar differ from the previous version by replacing the sliding support with an identical one in function - rigid. Due to the change in the type of supports, the type of stresses generated also becomes different, the rafter system turns into a spacer.
The puff is formed in the upper lobe of the arch. Its purpose is to endure no longer a stretch, but a compressive effect. Additional tightening, reinforcing the crossbar, is needed with a significant load. Arches with suspensions and struts complement the arch systems with headstocks. Such a system is needed for significant spans (from 6 to 14 m). The struts that correct the resulting bend must rest against the headstock. Regardless of the specific type of truss system, it is necessary to carry out all the details and their connections with each other as clearly as possible.
Not always hinged rafters can perform the task. Then the slanting elements come to the rescue. This type of rafters is used under hip roofs and under roofs equipped with a valley. Their length is longer than in the usual case. In addition, they become supports for the shortened rafters of the slopes. That is why the load on the rafters is about 50% more than in other structures.
Thanks to the increased length, it is possible to:
- resist significant impacts;
- form beams without cuts;
- bring the parts to a single size by pairing the boards.
To build a hip roof with many spans, the diagonal legs are provided with supports. Such supports are made in the form of standard struts or racks of timber, or a pair of connected boards. Support through a lining made of wood and a waterproofing layer is made directly on the reinforced concrete floor. The struts are placed at an angle of not less than 45 and not more than 53 degrees, at the bottom such a detail rests on the beds. The angle of installation is less important than the ability to fix parts of the rafters at the point experiencing the strongest load.
Sloping rafters placed in openings up to 750 cm should be held by struts only in the upper lobe. With a length of 750 to 900 cm, a truss truss or rack is additionally mounted below. And if the total span length exceeds 9 m, then for maximum reliability in the middle you need to put a rack, no other support will do. If the selected floor is unable to withstand the load, it will have to be reinforced with a beam. The type of support in the ridge is determined by how many intermediate supports are used, what they are, how the key layered rafters are made.
In addition to the type of rafters, you need to clearly understand their material. Both wooden and metal constructions can be good, but only each in its place. Even the high strength of the metal does not allow to push the usual wood. The tree has proven its benefits for thousands of years, and now it is even gaining popularity due to its excellent ecological characteristics. Boards and timber can be bought at an affordable price, and if something has not been taken into account, it is always easy to saw off the desired fragment or build up a part right on the construction site.
Sometimes there are problems associated with the operation of the created structures. Wooden rafters will have to be carefully treated with antiseptics, as well as means that block the development of mold colonies and insects. The combustibility of wood is suppressed due to regular processing, and in addition, it is too difficult to search for slopes longer than 7 m necessary accessories. Before installation, the walls are laid with a mauerlat, made from a log frame or based on a block of timber. The thickness of the structures is at least 180 mm, this is the only condition for a uniform distribution of loads.
Metal rafters are inevitably heavier than wood rafters for the same section. Therefore, the walls need to be strengthened, the work on their construction becomes more expensive and longer. It will not be possible to mount metal blocks manually; cranes will be required. It is impossible or very difficult to adjust the dimensions, the geometry of the rafters, so you will immediately have to build the walls as accurately as possible and eliminate errors during their construction. The slightest mistake can make an expensive block almost useless in practice.
Metal rafters are connected by welding, and welded joints are inevitably weakened, as corrosion develops rapidly there. The cost of the work is very high, and when performing them, it is necessary to comply with the requirements of fire and electrical safety. But there is undeniable advantage, as an opportunity to support a roof slope from 700 cm and longer. If you use a special anti-corrosion paint, the durability of metal structures is fully guaranteed. All these advantages allow you to quickly and comfortably build industrial building with considerable height and length of spans.
How to choose: what to consider?
The truss system should be chosen as correctly and clearly as possible.
When looking for a suitable solution, you need to pay attention to the following points:
- strength;
- the ability to support the slopes and the roof as a whole of a certain size and geometry;
- creating a positive aesthetic image of the building as a whole.
Technical parameters take precedence. Even the most beautiful structures that follow the principles of design will not show their positive qualities if they last too little. Experienced builders always analyze the average annual and seasonal temperatures, the financial capabilities of developers, the maximum possible wind speed and the severity of the overlying roof. The future use of the under-roof space and the scale required for it are also taken into account. Wind, snow and rain should not be underestimated, since these factors can have a very strong effect on the roof, and through it on the rafters.
If it is reliably known that a particular area is characterized by heavy snowfalls, the minimum slope angle is impractical. This point is even more relevant when using flat roofs. Under the pressure of accumulating precipitation, the frame can rapidly deform or water will pour inside. Another thing is when a certain region is often subject to the arrival of cyclones and the strong winds. Here the slope should already be made smaller, then the situation with the disruption of individual structural elements will be practically excluded.
You can avoid mistakes if you look at the already built nearby and long time operated houses. By accurately reproducing their roof structure and the rafter system interconnected with it, one can best take into account local specifics. But not everyone follows this path, sometimes the task is to develop an exclusively original project. Then you will have to carefully collect the initial data, carry out scrupulous calculations. In the absence of special knowledge, it is better to attract qualified performers to help.
After analyzing the total load created by wind and snow, it can sometimes be found that certain parts of the truss complex need selective reinforcement. When assessing the required angle of inclination of the roof, attention is also paid to the type of coating used. A heavy metal tile or corrugated board with a very large slope can spontaneously slide down, you have to additionally fix them, complicating your work and increasing the cost of installation. In addition, certain materials have a tendency to retain water or become soaked with it, which can only be combated by making the slope steeper. Creating a good roof and truss system that meets such conflicting requirements is not always accessible to non-specialists.
What does it consist of?
The structure of the truss system, as you can see, is quite complex and even contradictory. Each part of this design has a strictly defined role. So, Mauerlat is a long bars of coniferous wood, and strictly resinous wood is used for work. Such elements are laid out along the external load-bearing walls, attached to the base with anchors or rods of a special design (threaded). This part transfers the load from the roof to the wall.
Next comes such a device as a rafter leg. Under this name appears wooden beam used to build the contour of the slopes. The shape of the structure is always triangular, because it is the best way to help the roof withstand the destructive effects of winds, snow and other atmospheric processes. Rafter legs are placed at uniform distances along the entire roof, the step cannot exceed 120 cm.
A certain value for the support of the roof is also lying down - this wooden block replacing Mauerlat in some cases. Beds are placed on the internal supporting walls. They turn into the basis of the roofing triangle. Thanks to them, the slopes do not crawl under their own weight. And it is also worth mentioning about the racks - these are bars with a square section placed vertically. They perceive the pressure that comes down ridge knot, and transmit it mechanically to the inner carrier plane. Sometimes the racks are under the rafters.
Struts are designed to strengthen the entire structure of the roof, they connect the legs and beds into one whole. This detail is shaped like a rhombus. The community formed by the puff and struts is called the farm. In addition to them, you also need a crate, which is thin boards stuffed at right angles to the legs of the rafters. It helps to hold the rafter legs as single system. Absolutely any roof covering is attached to the crate.
Under soft materials the crate must be made inseparable, and best remedy considered plywood. At the very top is a ridge, which logically and physically completes the roofing triangle. The connection of a pair of opposing legs of the rafters is provided by a square piece of wood which prevents the entire roof from collapsing. And at the very bottom of the pitched roof there is an overhang, which extends approximately 0.5 m from the perimeter. Thanks to him, the streams of rain leaving the roof do not flood the outer bearing planes and do not harm them.
Fillies are used only in the situation when the rafter legs cannot be made along the length that would allow organizing the overhang. Connecting with boards of reduced section effectively solves this problem. For fastening the wooden elements of the rafters, it is most often recommended to use clamps, staples. It is undesirable to use nails, because the tree pierced by them becomes weak and fragile after a few years. Therefore, if professionals use connections made directly on the construction site, they use bolts.
But even a bolted connection weakens building structures, albeit relatively slightly. The strongest are the connections with the help of clamps or staples made of metal. To maximize the quality of products can only be their industrial production, since only in strictly standardized and fully controlled conditions deviations from the norms, deterioration in quality are excluded. You can assemble a truss structure from completely finished trusses very quickly, there is no risk in using it. Another thing is that it is required to collect information about the necessary characteristics as accurately as possible and transfer it to the manufacturer without distortion.
In addition to these elements, the truss system borders on the valley. This is the name of a special connection geometrically complicated roof at the points where its trajectory changes. The difference from the ridge is that in such places the roofing parts form a negative angle. The technical essence of the product lies in the fact that the gutter helps to divert liquid to the side. The more complex the configuration, the greater the number of such gutters should be.
The cornice bar serves to abut a strut against it, the other end of which rests against frontal board, while the dropper is not deformed and its configuration is not distorted. Wind connections are those elements of the truss system that transfer the load created by the wind from the roof to the foundation. They not only increase the overall stability of the structure, but also help to avoid tipping over in case of instability of individual parts. The roof will retain spatial rigidity even with very strong winds.
Horizontal wind connections are such elements as:
- braces;
- parabolic puffs;
- complexes of conventional puffs;
- trusses, complemented by a cross-shaped lattice.
Vertically, the preservation of characteristics under strong air pressure is ensured by wind supports and beams. Sometimes a monolithic reinforcing core is used. Engineers have come up with many other options for designing a wind connection. It is provided with frames and semi-frames, pinched props. In small buildings, rigid (resisting compression) or stretched diagonals are used, some covering two spans at once. The location of each of the elements is accurately reflected in the project documentation.
It is not so difficult to understand the qualitative characteristics of truss systems and their composition, if you show care and diligence. But it is equally important to calculate the quantitative parameters of these systems. If you do not do this or make the calculations incorrectly, you can either spend too much money, or encounter leaks, even with the destruction of individual elements.
- roof bends;
- average annual snow mass;
- unevenness in its distribution along the slopes, depending on the steepness of the slope and the wind rose;
- wind transfer of already fallen snow;
- descent of snow and ice masses, runoff of liquid water down;
- aerodynamic characteristics and windage of the structure;
- differences in the strength of the impact on individual points.
It is not so easy to calculate everything necessary, moreover, by simulating realistic situations and including a reasonable margin of safety in the project. Moreover, it is necessary to pay attention to the addition of various loads, to their cumulative effect. But still, any customer is quite capable of evaluating the quality of the work of designers. The loads applied to the truss systems are divided into three key groups: main, additional and extreme.
The main category includes:
- stable factors - the severity of the roof and roof structures, additional elements installed on top of them;
- long-term effects - snow, temperature;
- periodically changing factors - full calculations of snow and temperature effects, taking into account all the subtleties.
An additional group is the pressure exerted by the wind, builders and repairmen, ice and rain. The extreme category includes all natural and man-made emergencies that may occur in a particular place. Their level is predicted with a margin to ensure the exclusion of unpleasant consequences. When calculating the frame roof and the structures under it, the ultimate load is taken into account, if applied, the entire structure crumbles. Additionally, an indicator or a group of indicators is given, upon reaching which various deformations inevitably appear.
The snow drift coefficient reflects how much more snow will be deposited on the lee side and in front of objects (parts) that block the air flow. AT problem areas you will have to bring the rafters as close as possible and thoroughly calculate the required thickness of the front material. The most accurate assessment of all parameters can only be given by multiplying any received figures by the reliability factors. As for the wind, the force developed by it is aimed at dropping steep roofs and lifting from the leeward section of a flat roof. We must not forget that the air flow acts simultaneously on the facades and on the roof slopes.
When hitting the facade, the air breaks up into two waves: one goes down and is no longer of interest, and the other tangentially presses on the roof overhang, trying to raise it. The action on the slope occurs at a right angle, this area is pressed inward. At the same time, a vortex is formed, which tangentially affects the windward sector of the ramp. This vortex bypasses the ridge and begins to create lift already applied to the leeward segment. For your information: when calculating the mass of the roof, you need to take into account the severity of the rafters, insulation, waterproofing and vapor barrier.
The standard load per 1 square meter of the roof is up to 50 kg, regardless of its size and other significant circumstances. By changing the distance from one rafter leg to another, you can set the actual distribution of loads on them. According to most experts, indicators from 60 to 120 cm will be acceptable values. But on an insulated roof, it is worth choosing such distances that are equal to one sheet or roll of insulation materials. At the same time, it should be borne in mind that among several suitable options for arranging rafters, the one that gives the best effect with the minimum consumption of materials used is preferable.
When calculating the loads carried by the rafters, they always look at the fact that they do not exceed the ultimate endurance of the roofing material. After all, there is no point in such an excess. If, under the planned impact, the roof will still begin to sag, it is impossible to talk about a solid result. When calculating, the payload from structures connected to truss trusses is calculated according to the touch area that is plotted on the drawing. Such structures include ventilation chambers, attic and ground floor ceilings, and water tanks placed on the roofs. In addition to the amount of pressure on the rafter system, the sharpness of the roof slope is also calculated.
Tilt angle: value
On forums with consultations of specialists and in professional literature, one can find references to three units of measurement of inclination at once. In addition to the usual and expected degrees, there will be percentages and ratios between the parties. Often they get along together even within the same publication or instruction from the manufacturer of roofing materials. But in fact, there is nothing mysterious in this, any consumer can understand the essence. Under the angle of inclination of the roof, experts understand the angle that occurs at the intersection of the horizontal with the roof slope.
In this case, there can be no obtuse angles in principle. Moreover, you can meet a slope steeper than 50 degrees only in decorative elements, all kinds of turrets. An exception to general rule become only slopes on the lower rows of the rafters of the attic roof. In all other cases, the angles range from 0 to 45 degrees. The relative proportions of the sides are calculated as the ratio between the height of the slope and its projection on the horizontal. This indicator is equal to half the span for a uniformly constructed roof with a pair of slopes.
On a shed roof, the proportion is equal to one, but in more complex configurations, you still have to carry out all the calculations and estimates yourself, without starting from ready-made values. The slope angle is usually expressed as a fraction, with the numerator and denominator separated by a colon. But when the resulting numbers cannot be rounded to whole numbers, it is recommended to use percentages: they simply divide one by the other and increase it a hundred times. flat roofs those that have a slope of no more than 5 degrees are considered; a slope of 6–30 degrees is recognized as small, and all other roofs are considered to be steep. The flat design drastically increases usable area and is quite resistant to wind, but it will need to be manually cleaned of snow and strengthen the waterproofing to the limit. The slope is necessarily consistent with the specific material, and the required values \u200b\u200bcan be found in the instructions from the manufacturer. In order to calculate even the most complex and bizarre roof configurations, they are mentally divided into triangles and the angle is calculated separately in each.
Step, length and section of rafters
When it became clear how long the slopes are, what angles formed by these slopes with horizontal plane, it's time to do the actual miscalculation of the rafters. If the roof frame is made of a 5x15 cm timber under a metal tile, the mounting pitch sways from 0.6 to 0.8 m. As the slope grows, the gap also increases. If the roof slopes at 45 degrees, you need to put rafters every 800 mm, and for slopes of 75 degrees, you can add another 200 mm.
The next important parameter is the length of the rafters. It is closely related to the step: if the blocks are made long, they are brought together as much as possible, and when a single part is shortened, they are moved apart. When calculating the step of the crate, they proceed from the type of tiles laid on top and from the fact that an integer number of rows should be laid out on each slope. If you get a fraction, it is better to round, reduce or increase the indicator a little. The rafter legs under the metal tile, the cross section of which is 15x5 cm, range from 65 to 95 cm. You cannot increase the step when the cross section of the crate is 3x5 cm.
In order for the insulation to be better ventilated, rows of holes with a diameter of 1–1.2 cm are prepared in the region of the upper edge of the rafters. Ordinary rafters under the corrugated board go every 0.6–0.9 m. with significant cross section. The crate under the corrugated board is assembled from boards with dimensions of 3x10 cm, which are placed at intervals of 0.5 m. The interval must be calculated according to the height and thickness of the materials.
With all the revealed shortcomings of slate, it remains widely in demand. Under slate roof rafters with a section of 5x10–15 cm are mounted, 60–80 cm apart from each other. Most often, an average distance of 0.7 m is recommended. Pauses between parts of the crate are calculated according to the steepness of the material. On relatively flat areas, the support of 4 pieces of wood justifies itself. If the roof is made steeper, put 3 bars, separated by 63–65 cm.
We must not forget that due to the responsibility of the truss system, it is better to leave a margin of safety than to make an unreasonably weak type of rafters. For their manufacture, timber is used, dried to a maximum of 15%. A replacement for a beam can serve not edged board the same dryness. Under the ceramic tiles, a 5x5 cm timber crate is used. In the places marked according to the calculated distance, slate nails or simple self-tapping screws are used.
Installation: technology
The construction of the roof involves the use of a standard range of carpentry tools and an electric drill. If metal structures are used, a grinder will be required for precise cutting. Remember that it is impossible to process metal tiles or corrugated board with it, this can damage the material. A hipped roof without racks is made using puffs that reinforce the structure.
In the hip version, it is necessary to strengthen the runs running diagonally. Paired boards and a particularly strong timber are assigned to them. Connection points always have a support (rack), and main support placed about a quarter of the length separating the large rafters from the ridge. Under the gables on a gable roof, rafters of a shorter length are always made. But under the main part four-slope design extremely long parts can be placed, even more than 7 m. To keep them securely, either a rack is used that transfers stress to the ceiling, or a sprengel.
The first step in creating rafters under a broken roof is the formation of a support complex in the form of the letter P. It rests on the floor beams and is held by rafter legs. Next, they put three or more runs, two of them are brought to the corners of the frame, and the rest are placed in the middle of the overlap. The final step in raftering is fixing the legs. It is desirable to make truss systems according to a pattern - to connect two boards that are the same length as the rafters, and pin them to each other with a nail. The template is placed with its edges at the points of attachment of the rafter legs and fixed with a cross member.
An additional template (this time plywood) will help to make a mounting saw. Farms are attached to the Mauerlat, starting from the extreme ones. In order not to confuse with the attachment point of the ridge, the tops of these trusses are tied with a straight rope. The massiveness of the puffs increases as you approach the ridge. If the truss elements are bolted, washers or plates should be used. This will keep the nuts from digging into the wood.
How to install the rafters with your own hands, see the video below.
When designing any residential building, architects Special attention pay to the roof, as it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with the usual gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many are attracted more complex structures, which add a special attraction and originality to the structure. Other, more practical homeowners prefer attic structures, which are simultaneously capable of performing the role of a roof and a second floor.
The basis of any roof is an individual truss system, which has its own design features. Making the choice of the desired roof frame will be much easier if you figure out in advance which ones types and schemes of truss systems used in building practice. After receiving such information, it will become more clear how complex such structures are in installation. This is especially important to know if the roof frame is supposed to be built independently.
The main functional tasks of truss systems
When arranging pitched roof structures, the truss system is a frame for covering and for holding materials of the "roofing pie". With proper installation frame structure the necessary conditions will be created for the correct and non-insulated types of roofs that protect the walls and the interior of the house from various atmospheric influences.
The roof structure is also always the final architectural element of the exterior design of the building, supporting it with its appearance. stylistic direction. Nevertheless, the design features of the truss systems must first of all meet the requirements of strength and reliability that the roof must meet, and only then - aesthetic criteria.
The frame of the truss system forms the configuration and angle of inclination of the roof. These parameters largely depend on natural factors, characteristic for a particular region, as well as on the desire and capabilities of the homeowner:
- The amount of precipitation in different periods of the year.
- Direction and average wind speed in the area where the building will be erected.
- Plans for the use of space under the roof - arranging residential or non-residential premises in it, or using it only as air gap for thermal insulation of the rooms below.
- Variety of planned roofing material.
- Financial capacity of the homeowner.
Atmospheric precipitation and the strength of wind currents give a very sensitive load on the structure of the roof. For example, in regions with heavy snowfalls, you should not choose a truss system with a small angle of inclination of the slopes, as snow masses will linger on their surface, which can lead to deformation of the frame or roofing or leaks.
If the area where the construction will be carried out is famous for its winds, then it is better to choose a structure with a slight slope of the slope so that the sharp gusts that occur do not rip off individual elements of the roof and roof.
The main elements of the roof structure
Details and nodes of truss systems
Depending on the type of truss system chosen, the structural elements used can vary significantly, however, there are details that are present in both simple and complex roof systems.
The main elements of the pitched roof truss system include:
- Rafter legs forming roof slopes.
- - a wooden bar fixed on the walls of the house and serving to fix the lower part of the rafter legs on it.
- The ridge is the junction of the frames of two slopes. It is usually the highest horizontal roof line and serves as a support on which the rafters are fixed. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (run).
- Lathing - these are slats or beams mounted on rafters with a certain pitch and serving as the basis for the flooring of the selected roofing material.
- Retaining elements, where you can take beds, girders, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, link individual parts into a common structure.
In addition to the above structural details, other elements can be included in it, the functions of which are aimed at strengthening the system and optimal distribution of roof loads on the walls of the building.
The truss system is divided into several categories depending on the different features of its design.
attic space
Before proceeding to the consideration of different types of roofs, it is worthwhile to figure out what an attic space can be, since many owners successfully use it as utility and full-fledged living quarters.
The design of pitched roofs can be divided into non-attic and attic. The first option is called just that because the space under the roof has a small height and is used only as an air layer that insulates the building from above. Such systems usually include or have several slopes, but located at a very slight angle.
The attic structure, which has a sufficiently large ridge height, can be used in different ways, be insulated and not insulated. These options include attic or gable option. If a roof with a high ridge is chosen, then it is imperative to take into account wind loads in the region where the house is built.
Slope slope
To determine optimal slope slopes of the roof of the future residential building, first of all, you need to look at the already built low-rise neighboring houses. If they have been standing for more than one year and steadfastly withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set the goal of creating an exclusive original project, unlike the buildings standing nearby, it is necessary to familiarize yourself with the design and operational features of various truss systems and make appropriate calculations.
It should be borne in mind that the change in the tangent and normal values of the wind force depends on how large the slope of the roof slopes is - the steeper the angle of inclination, the greater the importance of the normal forces and the smaller the tangents. If the roof is sloping, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.
Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in conjunction with the wind load, since the snow load on the windward side will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will definitely collect, giving a big load on this area, so it should be strengthened with additional rafters.
The slope of the roof slopes can vary from 10 to 60 degrees, and it must be chosen not only taking into account the consolidated external load, but also depending on the roofing that is planned to be used. This factor is taken into account because roofing materials differ in their mass, their fixing requires a different number of elements of the truss system, which means that the load on the walls of the house will also vary, and how large it will be, also depends on the angle of the roof slope. Equally important are the features of each coating in terms of resistance to moisture penetration - in any case, many roofing materials need one or another slope to ensure the free flow of storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance how the cleaning process will be carried out and repair work on the roof.
When planning this or that angle of the roof slopes, you need to know that the fewer joints between the sheets of the coating, and the tighter they are, the less you can make the slope of the slope, of course, if it is not supposed to arrange a residential or utility room in the attic space.
If, however, a material consisting of small elements is used to cover the roof, for example, ceramic tiles, then the slope of the slopes must be made steep enough so that water never lingers on the surface.
Given the weight of the roofing material, you need to know - the heavier the coating, the greater the angle of the slopes should be, since in this case the load will be correctly distributed to the rafter system and load-bearing walls.
The following materials can be used to cover the roof: either a profile sheet, galvanized steel, corrugated asbestos-concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roofing and other roofing materials. The illustration below shows allowable angles steep slopes for various types roof coverings.
Basic structures of truss systems
First of all, it is worth considering the basic types of truss systems regarding the location of the walls of the house, which are used in all roof structures. The basic options are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.
fasteners for rafters
Layered system
In buildings where internal load-bearing walls are provided, a layered truss system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, fewer materials will be required for this design.
For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of the layered system can be equipped in three versions:
- In the first version, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the Mauerlat. Additionally, the rafters in the lower part are fixed to the wall with wire or staples.
- In the second case, the rafters in the upper part are cut at a certain angle and interconnected using special metal plates.
The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.
- In the third version, the rafters are rigidly fastened in the upper part with bars or processed boards located horizontally, parallel to each other on both sides of the rafters connected at an angle, and a ridge run is pinched between them.
In the lower part, sliding fasteners are used to fix the rafters, just as in the previous case.
It is necessary to explain why sliding fasteners are often used to fix the rafters on the Mauerlat. The fact is that they are able to save the load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they have the ability to move without deforming the overall structure of the roofing system.
This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.
However, in some cases, a spacer system is used for layered rafters, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and in order to remove the load from the walls, puffs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.
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