Fastening the rafters of a pitched roof: a thorough analysis of the components used. Self-construction of the roof of a private house Repair of rafter legs

The tempting simplicity of a roof with a single slope inspires thoughts of the opportunity to prove oneself in the field of a successful builder. The construction of a simple structure consists of banal installation rafter legs on supporting walls. No complex knots, tricky or numerous connections.

However, even in the simplest carpentry there are tricks that require thorough study. The future performer needs to know exactly how the stops are attached pitched roof to prevent deformation and damage to the elements of the frame system.

The design of the rafter frame of a pitched roof is extremely simple. It is a series of parallel laid boards or beams, resting their edges on two walls of different heights. For installation and fastening of rafter legs to building structure a transition element made of wood is used.

Depending on the type of box being installed and the wall material, the function of the transition element is performed by:

Mauerlat. In a shed roof scheme, these are two separately laid wooden beams that complete concrete or brick walls.
Upper harness frame structure. A belt made of double stitched boards or timber installed on top of the frame posts.
The upper crown of the foot, made of timber or logs.

The rafter legs and the elements in contact with them are made of wood, which has the property of changing its own dimensions following fluctuations in the background humidity and temperature changes. In spring and autumn, especially during the rainy season, the length of the rafter legs will be slightly longer than in dry summers and frosty winters.

Imagine what will happen if the rafters, rigidly fixed at the top and bottom, increase in size. Gaps will appear in the waterproofing, fasteners will become loose, slate sheets will move, or shift. In addition, deflection and heaving of the roof frame will certainly affect its wear resistance.

However, changes in the linear dimensions of the rafters are not at all the main problem with wooden rafter systems. An unpleasant surprise, if not taken into account, will be the settlement of the newly built box.

It is most pronounced in wooden walls, but it is also very typical for structures made of concrete and brick. Let us remember that pitched roofs rest on walls of different heights. Without calculations, you can understand that they will sag by different sizes. Those. there is a threat that, due to the difference in the subsidence of the walls, the new roof will not simply change the angle of the slope. There will be a possibility of disruption of nodes with extremely negative destructive consequences.

Despite the simplicity of pitched roofs and the close-to-horizontal direction of laying the rafters, the listed risks should not be forgotten. The nodes used to fasten the rafter legs of a pitched roof must take into account the “whims” of the wood.

Developer's work own project pitched roof is to find the right solution to three important problems, according to which:

It must be possible to move the wooden parts relative to each other.
Everything should be excluded probable reasons connection failures.
It is necessary to provide the rafters with the opportunity to adapt to the consequences of wall subsidence so that they can take a stable position.

The rafter legs of shed roofs erected over walls of equal height are classified as layered. The hanging type is used if the box being equipped has walls of equal height, and the slope is formed by rafter triangles.

Everything is clear about fastening the triangles: with the horizontal side they are installed on the harness or Mauerlat, they have a maximum joining area with the supporting elements, and are fixed in the usual way.

With layered rafter legs, everything is much more complicated. They are installed at an angle to the supporting elements. Without processing and preparation for installation, the rafters have only two unreliable points of contact with the strapping or Mauerlat.

No matter how powerful the fastener is, two points are not enough to firmly seat the part. Even with a slight impact, such a slope will simply slide down along with the continuous sheathing and multilayer sheathing. However, there are methods invented by ancient builders to avoid such troubles.

In order to prevent unwanted movements, the contact area between the rafters and the supporting element is increased, for this purpose the following is done:

Selection of cuts. These are cuts in the shape of a triangle or a triangle with a tooth. They are cut exclusively on the rafters, so as not to weaken the supporting mauerlat.
The top or bottom edge of the rafter leg is filed down, thereby creating a support platform that increases stability. Performed strictly vertically or horizontally.

Depending on the type and location of sawing or trimming, notches and cuts may or may not limit the movement of the wooden part. The restrictions are considered relative, because there are no absolutely rigid fastenings in the construction of pitched roofs. Experts classify the units used by degrees of freedom: from one to four.

In the construction of roofs with one slope, the following most often appear:

Fastening nodes with one degree of freedom are practically stationary connections that allow the rafter to rotate slightly around the fastening point.
Fastening units with two degrees of freedom are connections that provide the ability to rotate around the fastener and cause slight horizontal displacement.
Fastening units with three degrees of freedom are connections that allow rotation and displacement horizontally and vertically.

The presence of degrees of freedom does not mean that the rafter will be able to rotate and move freely in the area of the node. They are fastened quite rigidly, because they have to hold the sheathing, or another type of covering, or snow cover.

The connection will only show its capabilities if the load is exceeded. Then the rafter legs will just move and take a new position, and the system will remain without damage.

Any diagram of a pitched roof clearly shows us the presence of at least two connecting nodes. Let's divide them conditionally into upper and lower. In construction rafter roofs The rule applies: if one of the nodes is rigidly fixed, then the second should have more opportunities for movement.

Projecting and simplifying the technological principle, we can say: if the fastenings in the upper nodes of a pitched roof are made rigidly, then the lower connections must be freer to ensure the possibility of displacement when the pressure is exceeded. And vice versa: if the lower mount is practically motionless, then the rafter at the top needs to be provided with some reserve for movement and rotation.

After getting acquainted with the theoretical side of the issue of fastening the rafters of a pitched roof, you can begin practical research on the popular nodal schemes. Note that most projects of systems with a single slope are designed for the installation of rafters that form overhangs due to their own length. However, when covering large spans, it happens that the standard dimensions of lumber are not enough. In these cases, fillets are sewn to the rafters, creating an overhang. They are installed on the side of the installed leg and do not affect the principle of knot formation at all.

The second reason for using fillies in the formation of overhangs is that the rafters are too heavy, which is very difficult to lift and install. The third prerequisite lies in the features of the nodal fastenings: if the lower heel is installed on a slider with a trimmed edge.

No. 1: Support at the top and articulated bottom

A scheme with a rigidly fixed top and a relatively movable bottom is used in the construction of roofs over extensions, in the construction of objects with a steep roof and a significant difference between the heights of the supporting walls.

Simply put, where the top edge of the rafter rests on a wooden beam, there is no purlin or wall of the main building and no room for it to move. The lower node in such situations is calculated on a slider, allowing it to move slightly.

Algorithm for the classic version with the top resting on the purlin:

We install the supports of the purlin frame. For harness frame construction on opposite sides we install supports sewn from three pieces of 25x100 boards. The middle segment should be 75mm shorter than the outer ones in order to form a kind of recess.
We build a purlin frame. We place a 25×150 board of the required length into the recess.
We apply a 25×100 board of arbitrary length to the end of the future roof, but approximately 30 cm longer than the diagonal drawn from the top of the purlin to the frame. We mark the vertical line of the upper cut, outlining the adjacent edge of the purlin. We mark the line of the bottom cut and the vertical for trimming the edge of the rafter.
We cut out the rafter according to the marks, try it on after the fact, and, if necessary, adjust the cuts.
According to the template we made, we cut out and install the rafter legs.

We select the type of fastener based on the expected load. It is more convenient to fix the top with corners, the bottom with corners, screwing no more than three screws into them, or sliding supports. If necessary, the lower knot can be stabilized by sewing a support block to the rafter leg from below.

The connection point with the purlin can be designed slightly differently: the rafter is laid on the beam using a notch. Here the groove is selected strictly according to the size of the material. But if it is necessary to increase the degree of freedom, the horizontal wall of the notch is beveled at a slight angle, and the lower unit is equipped with a sewing strip.

No. 2: Top and bottom are articulated and fixed

The scheme is applicable when arranging boxes whose walls have already undergone intensive shrinkage. Suitable for isolated objects. The upper knot is made in the form of a triangular notch, the lower one is in the form of a cut with a tooth resting on the Mauerlat.

The process of constructing a lean-to rafter system:

We install the blank board edgewise on the mauerlat bars anywhere on the roof.
We lay a well-trimmed piece of board flat on the lower Mauerlat. We place it so that the outer edge coincides with the inner edge of the Mauerlat. Having outlined the scrap, we get an outline of the lower attachment point.
We transfer the trim to the area of the upper notch and outline it, because the lower heel of the rafter will decrease exactly by this amount.
The blank with the nodes drawn and then sawn will serve as a template. Using it, we produce the number of legs specified by the project.
We install the rafters. We fix them at the bottom with staples or pins, and at the top with corners.

If you need to increase the degree of freedom, by analogy with the previous method, the vertical edge of the upper notch will need to be slightly beveled. The cutting angle will then be not 90º, but 95 – 97º. Experienced carpenters make simple cuts directly on site, turning the workpiece upside down. Beginning performers should not imitate in the first stages.

The rafter template is used in roof construction only when there is no doubt about the geometric characteristics of the frame. In opposite situations, the rafters are tried on and made individually. First, the outermost elements of the system are installed, then the row legs along the cord stretched between them.

One of the variations on the theme of two hinged-fixed units involves the installation of a vertical cut at the top and a notch with a tooth at the bottom. Work on their installation is carried out as follows:

We install the blank board on the mauerlat so that its lower corner is directly above the outer edge of the beam.
At the top, using a piece of board, mark a vertical line (x) and measure its length.
We transfer the length of the upper cut to the area of the lower node. We set aside the length of the cut (x) vertically from the inner upper edge of the mauerlat.
From the resulting point we draw a horizontal line. The result is a notch with a tooth.
We cut out the nodes according to the marks, install them in place, fasten them with corners, duplicate the lower nodes with staples.

As the size (x) increases, the roof slope will increase, and as it decreases, it will decrease.

No. 3: Free top and hinged-fixed bottom

An ideal scheme for constructing a pitched roof with rafters, the edges of which extend beyond the walls. After some adjustments it can be used in the arrangement of extensions.

We install the workpiece edgewise on the upper and lower mauerlat beams with the edges moving beyond the walls. Here you need an assistant to hold the board up.
We apply a template - a trimmed piece of board sequentially to the lower and upper mauerlat so that the outer edge of the template coincides with the outer edge of the beams. We mark the lines of the upcoming cuts.
We select cuts according to the outlined lines. We slightly bevel the vertical wall of the upper notch.
We install the rafter, fix it at the top with nails or corners, and at the bottom with staples.
We manufacture and install the remaining rafters in the same way.

It is clear that mobility and its antagonist are relative concepts. However, one cannot treat them with lukewarmness. It is necessary to take into account the degree of freedom of the node both during the design period and when choosing fasteners. Lack of structural mobility will lead to deformation, excess will contribute to instability.

No. 4: Mobility of both attachment points

A scheme with two moving units can be used if both fastening connections have no more than two degrees of freedom. Those. horizontal mixing is prevented by restrictive devices installed at the top and bottom.

Let's consider an example in which the rafters of the extension are laid at the top into niches cut out in the wall. This means that horizontal displacement is excluded, rotation and some vertical movement are possible. The bottom is planted using notches, but is limited in the horizontal direction by metal corners.

Step-by-step actions of the builder of a single-slope building:

We are preparing the object for work. On the brick wall of the extension we place a mauerlat made of 100×150 timber. We lay it on the wide side closer to the inner edge of the wall. We fasten with anchors every 80cm. In the main wall of the building at the designed height, we cut out grooves for the upper heels of the rafters. The depth of the cuts is 12 cm, the step between them is 70 cm. If you don't want to bother with gouging, you can use metal brackets screwed to the wall.
Making a template for the rafter leg. Place the blank board with its upper edge in the groove and the lower edge on the mauerlat. Having retreated 10 cm from the lower corners of the workpiece in the horizontal direction, we draw two triangular notches.
According to the indications of the template, we make rafters. We install them, fixing the position with metal corners.

The device method is valid when covering spans up to 4.5 m. If you need to cover a larger span, the rafters will need a support group consisting of struts.

No. 5: Rigid attachment to an inclined harness

The method is used in frame construction, because the supporting element can only be laid at an angle on racks sawn at an angle. Either the racks of the frame itself or the cantilever-girder structure installed on the box are sawed down at an angle. Basically, last option quite suitable for constructing a pitched roof over concrete and brick walls.

Stages of installing a pitched roof using an inclined frame:

We assemble a structure that creates a roof slope. On the gable side of the frame building we install short posts with the top edge sawn at an angle.
On the sloping top of the racks we lay the board in one row for small outbuildings, two for more serious houses.
We equip the end sides of the roof with frames in the shape of a right triangle, the hypotenuse of which should follow the line of the slope.
We apply the rafter to the end of the roof to mark the line of the bottom gash.
Using the template, we make the required number of rafter legs. We install them on the harness, fixing the position of the elements with metal corners.

Without a shadow of a doubt, we classify the last method as the simplest category. Of all the methods of attaching rafters to the frame and beams of the Mauerlat of a pitched roof, this is the most conducive to attempts at independent implementation.

Final fastening work

After installing the entire row of rafter legs, we check the design position of the elements and the distances between them. We apply an arbitrary board flat to the frame of the ramp, identify shortcomings and correct the flaws. Then we fasten the rafters with staples or ties to the walls one at a time in regions with medium and low wind activity. We fix each leg in areas with high wind load.

The fillies, if they are planned for installation, are made of material with dimensions half smaller than the dimensions of the rafter legs. Sew them to the side of the rafter. The length of the sewn area is on average 60-80cm.

Video to visually study the process

The presented methods and schemes for fastening the rafters of a pitched roof have been tested in practice. They are most often used in " pure form" However, some adjustments according to specific technical conditions are not excluded.

The vast majority of frames for arranging roofs and laying roof coverings use ordinary wood purchased at the nearest warehouse or even just at a sawmill. This approach simplifies the life of builders and creates headache owners and residents, after a few years the rafter system has to be inspected and discarded individual elements and reinforce the rafters.

Why is inspection and periodic monitoring of the condition of rafter structures necessary?

Wood, like no other material, is suitable for assembling a roof frame, but wooden rafters turn out to be the most vulnerable part of the structure. In theory, wood can easily stand without losing its basic strength qualities for more than 50 years, but in practice, ensuring the safety of the rafter beam material is not so easy. The processes of wood rotting, deformation and cracking due to drying out and improper load distribution can often lead to a loss of load-bearing capacity of rafter structures.

The most critical areas of the rafter system can be counted on one hand:

Supporting part of the mauerlat and rafter legs;
Places of connections and fastenings of struts or struts, any load-bearing elements of the frame;
Places for rafter support on the ridge beam;
The middle parts of hanging rafter beams.

Important! You cannot use lumber taken directly from a sawmill or commercial warehouse to make rafters or other frame elements. Before use, the board and timber must dry under load in a folded bag.

In order to properly perform reinforcement, it is necessary to clearly understand the reasons why the frame begins to sag or lose strength:

If you assemble a rafter system from under-dried or “sick” material, the distribution of the load on the beams will be uneven, as a result, some of the beams will be overloaded, and some will work “idle”. Therefore, before trying to strengthen sagging or breaking rafters, it is necessary to remove and redistribute the load;
The lower half of the rafter legs is always in a more difficult condition, especially if the reinforcement during assembly was performed incorrectly. Any support points on the racks or struts, at the junction of the rafters with the mauerlat, force the rafter beam to work in the heaviest mode - with an alternating cyclic load. It is at this point that the wood fibers break and proper reinforcement is required;
Violation of ventilation conditions and removal of excess moisture from the under-roof space. In this case, the surface of the rafters becomes covered with cracks, which leads to intense absorption of moisture and the development of rotting and deformation processes.

In this case, strengthening is possible only by replacing the affected areas, installing support beams and elements.

Repair and strengthening of connections

Today in construction frame roofs Two main strengthening technologies are used - structural and repair. The structural type of reinforcement involves the use of methods for fastening linings, transitional and auxiliary elements, which allow turning a concentrated load into a distributed one. For example, the connection of rafters in the ridge can be done by fastening the ends of the beams with an overlap, but for layered rafter beams it is recommended to reinforce it by installing steel plates or boards fastened with at least 5-7 nails or bolts.

Structural reinforcement of rafters

It is very rare that it is possible to build a roof frame by simply installing rafters, without using reinforcement elements - struts and struts. Firstly, this method of device is suitable for very small buildings- country houses or bathhouses, and secondly, refusal to reinforce it will require the use of very massive and heavy beams and beams, which increases the cost of building a roof many times over. Even for a simple pitched roof, the architect must use reinforcement in the form of vertical supports and side struts.

Important! The most vulnerable and problem area are the connections between rafter beams and reinforcement elements. If the joined area is not executed correctly, deformation and destruction are inevitable.

For example, consider the option of strengthening a long rafter with a vertical post. If, instead of a movable support, as in the diagram, you use rigid fastening with an overhead plate, a bending moment is inevitably created at the fastening point in the ridge and the lateral load on the rafter beam increases. Instead of unloading, the result is a transfer and concentration of stress in the most vulnerable place - the central part of the beam.

The most difficult to calculate and making the right choice installations of power elements are round and polygonal frames, for example, a roof - a bay window or a conical outrigger. The photo above clearly shows how difficult and expensive it is to install rafters on a mauerlat.

The internal row of reinforcement of beams with support posts has its own tightening row and connection to the Mauerlat. The system of load-bearing beams is in many ways reminiscent of a hip structure, especially in terms of connecting the flanges with the corner frame of the valley. Due to the large length of the layered rafters, the builders used lengthening and at the same time strengthening the part of the beam located behind the fulcrum on the rack. Steel plates guarantee increased strength of the lower part of the slope.

Repair strengthening of rafter beams

The most simple example reinforcement is an increase in rafter length. The easiest way to get a long rafter is to connect two short beams with an overhead piece of board or timber. At the same time, reinforcement or connection using an oblique cut, which is widely used for Mauerlat boards, is not used in the rafters. The rafters connected in this way are not able to provide the necessary transverse rigidity of the beam.

An example of restorative or repair strengthening of rafters is the installation of a backing board under a beam that has delamination, cracks or residual deformation. In the most problematic cases, when it is impossible to replace the rafter beam, the load-bearing capacity is strengthened and restored using a prefabricated truss according to the diagram shown in the figure. Most often, this type of reinforcement is used for layered rafters.

The supporting surface is also subject to reinforcement, for example, if, due to insufficiently effective or improperly organized ventilation of the under-roof space, the condensate formed on the vapor barrier membrane flows to supporting surface wooden rafters on a mauerlat. If the supporting part of the beam is rotten or infested with pests, it is cut out and a steel frame, often called a prosthesis, is installed.

If destructive processes have also affected the Mauerlat, it is possible to change the single-support version to a double-support one. In this case, an additional beam is laid parallel to the main board of the Mauerlat, on which the reinforcing installed strut element rests, taking the lion's share of the load.

Often, subsidence and deformation of the frame occurs due to improper installation and fastening with nails in those places where it is necessary to use a threaded connection with steel plates - overlays. You should not remove old fasteners and try to restore the connection with new nails; this will give a temporary effect at best. Reinforcement is more reliable using overhead strips or metal plates with bent edges of the holes.

Conclusion

The basic rule of reinforcement is that the old fastening is not removed; in addition, “helpers” are installed - steel or wooden linings that absorb part of the forces. If their use does not give the desired effect, then you have to resort to installing full-fledged load-bearing frames and trusses, but again without dismantling the rafters.

Rafters perform a number of significant roofing functions. They set the configuration of the future roof, absorb atmospheric loads, and hold the material. Among the rafter's duties are the formation of smooth planes for laying the covering and providing space for the components of the roofing pie.

In order for such a valuable part of the roof to flawlessly cope with the listed tasks, information is needed about the rules and principles of its design. The information is useful both for those who are constructing 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 construction of the rafter frame for pitched roofs, wooden and metal beams. Source material For the first option, use a board, log, timber.

The second is constructed from rolled metal: channel, profile pipe, I-beam, corner. There are combined structures with the most heavily loaded steel parts and wood elements in less critical areas.

In addition to its “iron” strength, metal has many disadvantages. These include thermal qualities that are unsatisfactory to the owners of residential buildings. Frustrating need to apply welded joints. Most often, industrial buildings are equipped with steel rafters, and less often, private cabins assembled from metal modules.

In the matter of independent construction truss structures For private houses, wood is a priority. It is not difficult to work with, it is lighter, “warmer”, and more attractive in terms of environmental criteria. In addition, to perform nodal connections you will not need welding machine and welding skills.

Rafters - a fundamental element

The main “player” of the frame for constructing a roof is the rafter, which among roofers is called a rafter leg. Beams, braces, headstocks, purlins, ties, even a Mauerlat may or may not be used depending on the architectural complexity and dimensions of the roof.

Rafters used in the construction of gable roof frames are divided into:

Layered rafter legs, both heels of which have reliable structural supports under them. The lower edge of the layered rafter rests against the mauerlat or the ceiling crown of the log house. The support for the upper edge can be a mirror analogue of the adjacent rafter or a purlin, which is a beam laid horizontally under the ridge. In the first case, the rafter 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 - a tie. The latter connects the two lower heels of adjacent rafter legs, resulting in a triangular module called a rafter truss. Tightening dampens the tensile processes, so that only vertically directed load acts on the walls. Although a structure with hanging rafters is braced, the bracing itself does not transmit to the walls.

In accordance with the technological specifics of rafter legs, the structures constructed from them are divided into layered and hanging. For stability, the structures are equipped with struts and additional racks.

To support the top of the layered rafters, planks and purlins are installed. In reality, the rafter structure is much more complex than the elementary templates described.

Note that the formation of the frame of a gable roof can generally be done without a rafter structure. In such situations, the supposed planes of the slopes are formed by slabs - beams laid directly on the load-bearing gables.

However, we are now interested specifically in the structure of the rafter system gable roof, and it can involve either hanging or layered rafters, or a combination of both types.

Subtleties of fastening rafter legs

Fastening the rafter system to brick, foam concrete, aerated concrete walls is carried out through the Mauerlat, which in turn is fixed with anchors.

Between the Mauerlat, which is a wooden frame, and the walls made of the specified materials, a waterproofing layer made of roofing felt, waterproofing material, etc. is required.

The top of brick walls is sometimes specially laid out so that along the outer perimeter there is something like a low parapet. This is so that the mauerlat placed inside the parapet and the walls do not push apart the rafter legs.

The rafters of the roof frame of wooden houses rest on the upper crown or on ceiling beams. The connection in all cases is made by notches and is duplicated with nails, bolts, metal or wooden plates.

How to do without mind-boggling calculations?

It is highly desirable that the cross-section and linear dimensions of wooden beams be determined by the project. The designer will provide clear calculation justifications geometric parameters boards or timber, taking into account the entire range of loads and weather conditions. If available home handyman design development no, his path lies to the construction site of a house with a similar roofing structure.

You don’t have to pay attention to the number of floors of the building being constructed. It is easier and more correct to find out the required dimensions from the foreman than to find out them from the owners of a shaky self-built building. After all, in the hands of the foreman is documentation with a clear calculation of the loads per 1 m² of roof in a specific region.

The installation pitch 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 laying clay tiles, for example, the optimal distance between the rafters will be 0.6-0.7 m, and for corrugated sheets 1.5-2.0 m is acceptable.

However, even if the pitch required for proper 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 understand the pitch of the rafters before constructing the rafter system.

Craftsmen calculate the pitch of the rafters according to design features buildings, simply dividing the length of the slope into equal distances. For insulated roofs, the pitch between the rafters is selected based on the width of the insulation slabs.

You can find it on our website, which may also help you a lot during construction.

Rafter structures of layered type

Layered rafter structures are much simpler to construct than their hanging counterparts. A reasonable advantage of the layered scheme is to ensure adequate ventilation, which is directly related to long-term service.

Distinctive design features:

It is mandatory to have support under the ridge heel of the rafter leg. The role of support can be played by the run - wooden beam, resting on racks or on the internal wall of the building, or the upper end of an adjacent rafter.
Using a Mauerlat to erect a truss structure on walls made of brick or artificial stone.
The use of additional purlins and racks where the rafter legs, due to the large size of the roof, require additional support points.

The disadvantage of the scheme is the presence of structural elements that affect the layout of the internal space of the attic in use.

If the attic is cold and it is not intended to organize useful rooms, then the layered structure of the rafter system for installing a gable roof should be given preference.

Typical sequence of work for the construction of a layered truss structure:

First of all, we measure the heights of the building, the diagonals and horizontality of the upper cut of the frame. When identifying vertical deviations of brick and concrete walls, we remove them with a cement-sand screed. Exceeding the heights of the log house is cut off. By placing wood chips under the mauerlat, vertical flaws can be combated if their size is insignificant.
The floor surface for laying the bed must also be leveled. It, the Mauerlat and the girder must be clearly horizontal, but the location of the listed elements in the same plane is not necessary.
We treat all wooden parts of the structure with fire retardants and antiseptics before installation.
We lay waterproofing on concrete and brick walls for installation of the Mauerlat.
We lay the mauerlat beam on the walls and measure its diagonals. If necessary, we slightly move the bars and turn the corners, trying to achieve the ideal geometry. Align the frame horizontally if necessary.
We mount the Mauerlat frame. The beams are joined into a single frame using oblique notches; the joints are duplicated with bolts.
We fix the position of the Mauerlat. Fastening is done either with staples to wooden plugs placed in the wall ahead of time, or anchor bolts.
Mark the position of the prone position. Its axis should recede from the mauerlat bars at equal distances on each side. If the run will rest only on posts without supports, we carry out the marking procedure only for these posts.
We install the bed on a two-layer waterproofing. We fasten it to the base with anchor bolts, with internal wall We connect with wire twists or staples.
We mark the installation points of the rafter legs.
We cut out the racks to uniform sizes, because... Our bed is exposed to the horizon. The height of the racks should take into account the cross-sectional dimensions of the purlin and beam.
We install racks. If provided by the design, we secure them with spacers.
We lay the purlin on the racks. We check the geometry again, then install brackets, metal plates, and wooden mounting plates.
We install a test rafter board and mark the cutting areas on it. If the Mauerlat is set strictly to the horizon, there is no need to adjust the rafters on the roof after the fact. The first board can be used as a template for making the rest.
We mark the installation points of the rafters. For marking, folk craftsmen usually prepare a pair of slats, the length of which is equal to the clearance between the rafters.
According to the markings, we install the rafter legs and fasten them first at the bottom to the mauerlat, then at the top to the purlin to each other. Every second rafter is screwed to the Mauerlat with a wire bundle. In wooden houses, the rafters are screwed to the second crown from the top row.

If the rafter system is made flawlessly, the layer boards are installed in any order.

If there is no confidence in the ideal structure, then the outer pairs of rafters are installed first. A control string or fishing line is stretched between them, according to which the position of the newly installed rafters is adjusted.

The installation of the rafter structure is completed by installing fillets, if the length of the rafter legs does not allow forming an overhang of the required length. By the way, for wooden buildings the overhang should “extend” the contour of the building by 50 cm. If you plan to organize a canopy, separate mini-rafters are installed under it.

Another useful video about building a gable rafter base with your own hands:

Hanging rafter systems

The hanging variety of rafter systems is a triangle. The two upper sides of the triangle are folded by a pair of rafters, and the base is the tie connecting the lower heels.

The use of tightening allows you to neutralize the effect of the thrust, therefore, only the weight of the sheathing, roof, plus, depending on the season, the weight of precipitation, acts on walls with hanging rafter structures.

Specifics of hanging rafter systems

Characteristic features of rafter structures hanging type:

The obligatory presence of a tie, most often made of wood, less often of metal.
Possibility to refuse to use the Mauerlat. A timber frame can be successfully replaced by a board laid on double-layer waterproofing.
Installation of ready-made closed triangles – trusses – on the walls.

The advantages of the hanging scheme include the space under the roof free from racks, which allows you to organize an attic without pillars and partitions. There are disadvantages.

The first of them is restrictions on the steepness of the slopes: their slope angle can be at least 1/6 of the span triangular truss, steeper roofs are strongly recommended. The second disadvantage is the need for detailed calculations for the proper installation of cornice units.

Among other things, the angle of the truss will have to be installed with pinpoint precision, 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 backing board replacing it.

Subtleties of long-span hanging systems

The tie is the longest element of a hanging rafter structure. Over time, as is typical for all lumber, it becomes deformed and sags under the influence of its own weight.

Owners of houses with spans of 3-5 meters are not too concerned about this circumstance, but owners of buildings with spans of 6 meters or more should think about installing additional parts that exclude geometric changes in tightening.

To prevent sagging, there is a very significant component in the installation diagram of the rafter system for a long-span gable roof. This is a pendant called a grandmother.

Most often it is a block attached with wooden pegs to the top of the truss. The headstock should not be confused 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 is not used.

The bottom line is that the headstock hangs, as it were, on the ridge assembly, and a tightening is attached to it using bolts or nailed wooden plates. To correct sagging tightening, threaded or collet-type clamps are used.

The tightening position can be adjusted in the area of the ridge assembly, and the headstock can be rigidly connected to it by a notch. Instead of a bar in non-residential attics, reinforcement can be used to make the described tension element. It is also recommended to install a headstock or hanger where the tie is assembled from two beams 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 proper placement of vector loads acting on the system.

As a result, the rafter system is stable with minor and not too expensive modernization.

Hanging type for attics

In order to increase usable space the tightening of the rafter triangles for the attic is moved closer to the ridge. A completely reasonable move has additional advantages: it allows you to use the puffs as a basis for lining the ceiling.

It is connected to the rafters by cutting with a half-pan and duplicating with a bolt. It is protected from sagging by installing a short headstock.

A noticeable disadvantage of the attic hanging structure is the need accurate calculations. It is too difficult to calculate it yourself; 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 rafter systems cannot be the same, because:

In the construction of a layered structure, a board or beam of small cross-section is used to make rafter legs. Because layered rafters have two reliable supports underneath 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. To make a tightening, a material with a similar cross-section is required. Even taking into account the abandonment of the Mauerlat, the consumption will be significantly higher.

It will not be possible to save on the grade of material. For the load-bearing elements of both systems: rafters, purlins, beams, mauerlat, headstocks, racks, 2nd grade lumber is needed.

For crossbars and tensile ties, grade 1 will be required. In the manufacture of less critical wooden overlays, grade 3 can be used. Without counting, we can say that in the construction of hanging systems, expensive material is used in greater quantities.

Hanging trusses are assembled in an open area next to the facility, then transported, assembled, upstairs. To lift weighty triangular arches from timber, you will need equipment, the rental of which will have to be paid. And the project for complex nodes of the hanging version is also worth something.

Video instruction on the installation of a hanging category truss structure:

There are actually many more methods for constructing rafter systems for roofs with two slopes.

We have described only the basic varieties, which in reality are applicable for small country houses and buildings without architectural tricks. However, the information presented is enough to cope with the construction of a simple truss structure.

The rafters serve as the basis for the entire roofing structure, and their installation is one of the most important tasks when building a house. The frame of the future roof can be made and installed independently, observing the technological features of roofs of different configurations. We will present the basic rules for the development, calculation and selection of a rafter system, and also describe the step-by-step process of installing the “skeleton” of the roof.

Rafter system: rules for calculation and development

Rafter system - Basic structure, capable of resisting gusts of wind, taking on all external loads and evenly distributing them onto the internal supports of the house.

When calculating the truss structure, the following factors are taken into account:

Roof angle:
- 2.5-10% - flat roof;
- more than 10% - pitched roof.
Roof loads:
- permanent - total weight all elements of the “roofing cake”;
- temporary - wind pressure, the weight of snow, the weight of people carrying out repair work on the roof;
- force majeure, for example, seismic.

The amount of snow loads is calculated based on the climate characteristics of the region using the formula: S=Sg*m, Where Sg- weight of snow per 1 m2, m-calculation coefficient (depending on the slope of the roof). The determination of wind load is based on the following indicators: type of terrain, regional wind load standards, building height.

Coefficients, necessary standards and calculation formulas are contained in engineering and construction reference books

When developing a rafter system, it is necessary to calculate the parameters of all components of the structure.

Elements of the truss structure

The rafter system includes many components that perform a specific function:

Materials for making rafters

Rafters are most often made from coniferous trees (spruce, larch or pine). For roofing, well-dried wood with a humidity level of up to 25% is used.

The wooden structure has one significant drawback- over time, rafters can become deformed, so metal elements are added to the supporting system.

On the one hand, metal adds rigidity to the rafter structure, but on the other hand, it reduces the service life of wooden parts. Condensation settles on metal platforms and supports, which leads to rotting and damage to the wood.

Advice. When installing a rafter system made of metal and wood, care must be taken to ensure that the materials do not come into contact with each other. You can use moisture-proofing agents or use film insulation

In industrial construction, metal rafters made of rolled steel (I-beams, T-beams, angles, channels, etc.) are used. This design is more compact than wood, but retains heat less well and therefore requires additional thermal insulation.

Choosing a rafter system: hanging and suspended structures

There are two types of rafter structures: hanging (spacer) and layered. The choice of system is determined by the type of roof, floor material and natural conditions of the region.

Hanging rafters rest solely on the external walls of the house, intermediate supports are not used. Hanging type rafter legs perform compression and bending work. The design creates a horizontal bursting force that is transmitted to the walls. Using wooden and metal ties you can reduce this load. The ties are mounted at the base of the rafters.

A hanging rafter system is often used to create an attic or in situations where roof spans are 8-12 m and additional supports are not provided.

Layered rafters are installed in houses with an intermediate columnar support or an additional load-bearing wall. The lower edges of the rafters are fixed to external walls, and their middle parts are on the inner pier or supporting pillar.

Installation of a single roofing system over several spans should include spacer and layered roof trusses. In places with intermediate supports, layered rafters are installed, and where there are none, hanging rafters are installed.

Features of arranging rafters on different roofs

Gable roof

A gable roof, according to building codes, has an inclination angle of up to 90°. The choice of slope is largely determined by the weather conditions of the area. In areas where heavy rainfall prevails, it is better to install steep slopes, and in areas where strong winds prevail, flat roofs are installed in order to minimize the pressure on the structure.

A common version of a gable roof is a design with a slope angle of 35-45°. Experts call such parameters the “golden mean” of consumption. building materials and load distribution along the perimeter of the building. However, in this case attic space It will be cold and it will not be possible to arrange a living room here.

For a gable roof, a layered and hanging rafter system is used.

Hip roof

All roof slopes have the same area and the same angle of inclination. There is no ridge girder here, and the rafters are connected at one point, so the installation of such a structure is quite complicated.

It is advisable to install a hip roof if two conditions are met:

the base of the building is square in shape;
in the center of the structure there is a load-bearing support or wall on which it will be possible to fix a rack that supports the junction of the rafter legs.

Create hip roof It is possible without a rack, but the structure must be strengthened with additional modules - racks and puffs.

Hip roof

The traditional design of a hip roof involves the presence of slanted rafters (diagonal) directed towards the corners of the building. The slope angle of such a roof does not exceed 40°. Diagonal runs are usually made with reinforcement, since they account for a significant part of the load. Such elements are made from double boards and durable timber.

The joining points of the elements must be supported by a stand, which increases the reliability of the structure. The support is located at a distance of ¼ of the length of the large rafters from the ridge. Shortened rafters are installed in place of the gable roof gables.

The rafter structure of a hipped roof can include very long diagonal elements (more than 7 m). In this case, a vertical post must be mounted under the rafters, which will rest on the floor beam. You can use a truss as a support - the beam is located in the corner of the roof and fixed to adjacent walls. The truss truss is reinforced with struts.

broken roof

Sloping roofs are usually created to accommodate a larger attic. The installation of rafters with this roofing option can be divided into three stages:

Installation of a U-shaped structure - supports for purlins that hold the rafter legs. The base of the structure is floor beams.
At least 3 purlins are installed: two elements run through the corners of the U-shaped frame, and one (ridge purlin) is mounted in the center of the attic floor.
Installation of rafter legs.

Gable roof: do-it-yourself rafter installation

Calculation of inclination angle and loads

Of course, you can calculate a gable roof yourself, but it’s still better to entrust it to professionals in order to eliminate errors and be confident in the reliability of the structure.

When choosing the angle of inclination, it is necessary to take into account that:

an angle of 5-15° is not suitable for all roofing materials, so first choose the type of coating, and then calculate the rafter system;
at an angle of inclination over 45°, material costs for the purchase of components of the “roofing cake” increase.

Load limits from snow exposure range from 80 to 320 kg/m2. The design coefficient for roofs with a slope angle of less than 25° is 1, for roofs with a slope from 25° to 60° - 0.7. This means that if there are 140 kg of snow cover per 1 m2, then the load on a roof with a slope at an angle of 40° will be: 140 * 0.7 = 98 kg/m2.

To calculate the wind load, the coefficient of aerodynamic influence and vibration is taken wind pressure. Meaning constant load is determined by summing the weight of all components of the “roofing cake” per m2 (on average 40-50 kg/m2).

Based on the results obtained, we find out the total load on the roof and determine the number of rafter legs, their size and cross-section.

Installation of Mauerlat and rafters

Do-it-yourself installation of rafters begins with the installation of a mauerlat, which is fixed with anchor bolts to the longitudinal walls.

Further construction of the structure is carried out in the following sequence:

Installation of rafters: video

Methods for connecting rafter structure elements: video

Strengthening truss structures may be required in cases where errors were made at the design or construction stage of the structure. Incorrectly calculated loads or material properties can lead to partial deformation of the roof, or even to its complete destruction. In this case, strengthening the rafters becomes an urgently needed procedure that can save your home.

The rafters, which are the basis of any roof, must be periodically checked for any defects or damage caused by the use of the roof. If any are detected, it is necessary to strengthen and strengthen the rafter system of the house, garage, barn, bathhouse or other buildings. Errors during installation and calculations can occur with any type of rafter system, so home craftsmen need the ability to strengthen rafters for each of them.

Strengthening rafter legs

Strengthening rafters can be done in several ways, the main ones will be discussed in detail below. These methods can be used individually or in combination. In each specific case, homeowners must decide for themselves this question. But it is best not to save money and take into account that the destruction of the roof above the same garage can damage the car and cause significant material damage, not to mention the danger of deformation of the roof structure of the house.

So, strengthening of load-bearing functions is carried out using:

“help”, beams that take on part of the loads on the rafter structure;
installation of struts;
double-sided overlays.

Supports are installed in cases where incorrect calculations of the loads on the rafters were carried out, and as a result an increase is required cross section beams holding the structure of the entire roof. It is quite easy to carry out such reinforcement; to do this, you need to install this additional beam and secure it between the Mauerlat and the rafter leg. It is fastened either with bolt clamps or with special steel plates with teeth.

The place where the rafter leg is placed on the brace also requires special attention from the homeowner, since it is in this place that the maximum bending pressure occurs. For clarity, remember how as a child you broke a stick over your knee; it is the knee that plays the role of the brace. To reduce the load and the risk of deformation of continuous rafters in the place where they rest on the strut, we recommend increasing the cross-section of the beam by covering it with overlays from boards. The thickness of the overlays depends on the calculation of the required cross-section for the structure under the planned bending loads. The rafters are connected to reinforcing linings using various fasteners, but more often with nails or special bolts. If at the same time the length of the support is extended beyond the fulcrum, then it is possible to increase not only the strength of the beam, but also the entire connecting unit.

Sometimes a project may have an error in determining the angle of the roof slope, and operation reveals this miscalculation. For example, if the slope is not steep enough, snow accumulates, which can damage the roof. In this case, it becomes necessary to make some changes to the design of the rafters. To do this, new parts of the rafters are attached to the old elements using plank walls and nails, due to which the newly formed trusses become more rigid and change the slope of the roof in the desired direction.

This method will allow you to make changes without having to disassemble the entire roof again; however, you won’t be able to make any special changes to the under-roof space, since you won’t be able to either enlarge it or configure it in any way.

Strengthening the lower parts of the rafters

The roof truss structure of any building is most vulnerable in its lower part, which is where it most often requires reinforcement - this is the bottom of the rafters and the mauerlat beam. The reason for this vulnerability is that it is in the contact area between wood and brickwork that condensation most often forms and moisture enters if the integrity of the roof is damaged. Another reason is the use of low-quality wood, which was either raw or dried in violation of technology. All this leads to the formation of putrefactive processes in the wood and its destruction. Therefore, during construction it is important to pay attention to the choice quality material and provide reliable hydro- and vapor barrier. The absence or improper functioning of ventilation ducts can also cause moisture accumulation and wood destruction.

In this case, struts are used to strengthen the roof frame. They are attached to the lower end of the rafter leg and rest against the mauerlat or leg. The number of such additional struts depends on your situation. To give additional stability, the struts are attached slightly at an angle, that is, their lower part extends slightly to the sides. It is the support in the bed that will allow you to remove the effect of bending deformation on the span of the rafters in this part.

Strengthening rotted parts of the rafter system

If you still cannot protect yourself from the destructive effects of rot on wood, you can try to strengthen the damaged areas of the rafters or mauerlat of your house or garage. If we are talking about one case of damage to the rafters, then you can get by with wooden plank overlays. They are fastened with nails or bolts, while the lower part of the board of the lining should rest against the Mauerlat, to ensure additional reliability of fixation, and it is better to attach the linings in this place to the Mauerlat using steel wire.

But if we are talking about massive damage to the rafters, when deformation or rot is found on many rafters, then it is necessary to apply special system prostheses. These prostheses are made of steel rods and are attached to an undamaged area of the structure, while the deformed part is simply removed. For this operation, it is necessary to fix the rafter with special temporary supports and remove the damaged part (for this you will have to disassemble part of the roof). Then you should cut out a similar size prosthesis from the same wood and install it in place of the removed area, its lower part should rest against the Mauerlat. The steel rods of the prosthesis provide additional fixation of the entire structure.

If strengthening with partial replacement requires not the rafter leg, but the mauerlat, then the following manipulations must be carried out:

are fixed with temporary supports of the rafters of the roof frame;
the rotten section of the Mauerlat is cut out and removed;
steel spikes are driven into the masonry, onto which a beam of the required cross-section, at least one meter long, is laid;
a piece of beam equal to the length of the beam is installed on the ceiling;
then the rafter leg is fixed on both sides with struts, which rest on the newly installed beam.

Work to strengthen the rafters of any roof is the whole complex work, which includes various operations to correct deformation and destruction of the wooden elements or places of their fastening.

Deformations are most often expressed through curvature and the formation of cracks in the beams and boards of rafters and other wooden roof elements, but sometimes intervention is required when it is necessary to correct poor-quality fastening of parts of the system to each other.

In the latter case, it is worth paying attention to the key connection points. First of all, make sure that the rafters and ridge of your roof are properly secured; problems in this area often arise if you are not careful during installation.

When correcting defects, it is necessary to achieve the tightest possible connection between the rafters and ridge beam, using a special jack can help with this. To qualitatively strengthen this unit, various techniques are used. This unit is fastened using either a special steel strip with perforated holes, or various wooden planks, or by placing the rafters on a steel fastening bolt. In each of these methods, several options can be distinguished, for example, wooden overlays can be attached both above and below the ridge beam; there are also several types of metal plates for reliable fixation of rafters and overlays.

There are some secrets when correcting the deflection of rafters. To do this on inside Special wooden stops are securely fastened to the beams, after which the rafters are straightened using a jack, and strong spacers are inserted between them one by one. Such a system will help to resist external pressure on the roof and rafters and stop the deformation of the latter.

When strengthening the legs of the rafters through timber extensions, it is necessary to correctly select its parameters. It should be either equal in width to the rafters or slightly wider. For ease of installation, the timber is fastened with self-tapping screws to the rafter beam, and then holes are made through both elements, after which the entire structure is mounted on special steel bolts or studs.

It is better to drill these holes in a staggered pattern, which increases the structure’s resistance to loads during bending deformation. The diameter of the drill and mounting pins must be equal. Fastening is done with steel studs, self-locking nuts and washers. This design is not only easy to install, but also reliable in operation. It will not come loose and will last as long as the wood can withstand.