How to install ridge beams? How to splice a ridge run? Installation of ridge beams

How to install ridge beams? How to splice a ridge run? Installation of ridge beams
18.10.2019

When building a house, there are practically no elements or connecting nodes that are not particularly important, since the overall reliability of the structure in one or another area depends on each of them . Splicing rafters in the ridge area is a rather complex task that can be accomplished in various ways. The master usually chooses the most reliable one, applicable for a particular structure.

You should always remember that any mistakes made during installation work during the construction of the roof structure, from the rafter system to the roofing material, will sooner or later negatively affect the quality of the entire building. Therefore, when drawing up a house project, it is necessary to think through the connection of each of the nodes. And it is especially important to choose reliable fastening of the rafter legs when forming the ridge.

A few words about the basic design of the rafter system

First of all, you need to pay a few minutes of attention to the general structure of the rafter system in order to remember what its main elements are called, since in the further description of installation work they will appear quite often.

  • Mauerlat - This is a beam fixed to a load-bearing wall. It serves to secure the lower side of the rafter leg to it, and to evenly distribute the load from the entire roofing system onto the walls.

Mauerlat - a reliable basis for the rafter system

This element of the rafter system must be correctly selected and fixed to the wall, since the reliability of the installation of all other load-bearing parts depends on this. How to install is described in detail in the corresponding publication on our portal.

  • Rafter legs or simply rafters - they form the frame of the slope, are fixed to the Mauerlat in the lower part, and from above - on the ridge girder or between themselves, forming the ridge.
  • Ridge run is fixed on a stand supported by struts. It is designed for rigid fastening of rafters.
  • Puff - This is a horizontal beam that additionally connects a pair of rafter legs, giving the structure additional rigidity. Tightenings are of particular importance in hanging rafter systems, when it is impossible to create intermediate supports on main walls. Ties placed between two mauerlat beams are often used as attic floor beams. Installed closer to the ridge, they can serve as the basis for lining the attic ceiling.
  • Struts and help - These are reinforcing elements designed to give the truss of the rafter system additional rigidity and strength. Usually used in cases where a large length of rafter legs is required, more than 5 ÷ 6 meters.

  • Rack it is used as a support for the ridge girder and is most often installed in each of the trusses if a layered rafter system is being erected, which has additional supports in the form of capital intra-house partitions.
  • Lezhen - This is a beam laid on the load-bearing partitions of the house, and intended for attaching racks or struts to it.

The importance of correct fastening of the rafters on the ridge

An element such as a ridge is present in the design of most types of roofs. It is not in the tented, vaulted and

rafter mount


The ridge is the highest point of the roof, at which the elements that form the slopes - rafters - are connected. Therefore, the main mission of the ridge unit is to impart strength and rigidity to the entire rafter system. Depending on how correctly the fastening is done, the operation of the roof structure will be longer without the need for repairs.

Basic methods of installing rafters

Installation on the load-bearing walls of a building can be done in various ways, which you need to have an idea about before choosing the type of connections for the load-bearing elements of the ridge slopes:

  • The rafters and tie are connected into a triangle on the ground, and then lifted onto the box of the house in finished form, where they are secured to the mauerlat laid on the walls. The installed trusses are connected to each other by side slopes or ridge girders.

  • Two extreme triangular trusses are assembled on the ground, which will go to the end, gable sides of the structure. Then they rise up and are fixed on the Mauerlat. The upper ridge corners of two opposite trusses are connected by a stretched cord, which becomes a kind of level along which the remaining middle rafter pairs, assembled on site, will be placed. After this, the assembled trusses are connected by a ridge girder.

  • All elements are lifted onto the floor separately and assembled at the place of their installation. In this case, vertical posts are installed on the end walls, in the center, setting the height of the ridge. Then the racks are connected to each other by a ridge girder, onto which the rafter legs are secured.

If the rafters are connected on a purlin, then they do not require control using a tension cord. Therefore, the racks and purlins must be set very carefully, level and plumb, at right angles to each other.

Types of rafter connections on the ridge

As mentioned above, there are several ways to connect rafters when forming a ridge, and different fasteners are used for this purpose.

The main options in private housing construction include three types of connections:


  • “Half-tree” cutting, when half of its thickness is selected at the edges of the rafter beam. These selected sections are superimposed on each other and fastened with one of the fasteners suitable for this case, for example, twisted with a bolt passed through.

  • Overlapping - the ends of the rafters overlap each other and are fixed together with a through fastener.

  • Trimming the end sides of the rafters - this method of connections is performed most often. It is carried out by laying rafters overlapping each other, then they are simultaneously trimmed. This creates an even cut of two rafters at the same angle in a mirror image, so they fit perfectly together.

It should be noted that there are other connection methods, for example, “tenon and groove” or end-to-end to the ridge girder, possibly with additional bars or boards attached to the girder for additional strength between the rafters.


Often one of the sides of the rafter leg, upper or lower, is fixed to movable fastenings, hinged (top) or sliding (bottom). It is important to consider this in cases where the roof is installed on a newly built house, especially a log house. This approach is due to the fact that in the first years of operation the structure usually shrinks, and if rigid fastening is used, the roof structure may be damaged or deformed, since the “geometry” of the system will change and the distribution of loads will be disrupted.

Read the advice of professionals on which one is better to choose in our new article on our portal.

Elements for fastening rafters on the ridge

There are many options for fastening rafters to each other or on a ridge run - they can be rigid or hinged. To decide on their choice, you need to know what they are and what rafter connections they are suitable for.

To fix rafters in the ridge area, fasteners such as overlays made of metal or wooden plates, beams, metal corners of various configurations, staples, movable fasteners, wooden wedges, and nail plates are used. These fasteners are secured with self-tapping screws, screws, bolts and nails. The choice of fasteners mainly depends on the chosen connection design.


Bolt fixation

Fixing the rafters on the ridge with one bolt allows them to move to one side or the other relative to the axis when the structure shrinks. If such a fastening is used in the upper part, the lower side of the rafter leg must have a rigid installation on the mauerlat.

  • The diagram presented above, number one, shows the connection of the rafters using the tongue-and-groove method and fastened with a bolt, allowing them to have a slight play relative to each other when the building shrinks.

It should be especially noted that this method is suitable for light, cold roofs that will not be burdened with a heavy load, since the rafters in the fastening unit are somewhat weakened by the cutouts for the tongue-and-groove connection and the through hole drilled in them.

  • The sixth picture of the diagram also shows the fastening of the rafters with a bolt, but in this case they are installed with each other “overlapping”, and on the run - using the cutting method. This fastening method gives a smaller range of displacement, but it is still possible within certain limits. In this version, the rafters are less weakened, since they do not have cutouts for connections and can withstand greater loads. However, it is still not recommended to use this connection technology for roofs with a large slope area.

  • If you plan to make a rigid fastening in the ridge part of the rafter legs fitted at the end part using bolts, then two fasteners are used, installed in through holes, through two metal plates, which are mounted on both sides of the connection.

  • If you want to make the connection of rafters installed overlapping and fixed with one bolt rigid, additional fasteners are used - metal corners attached to the ridge girder.
Fastening rafters with plates

The diagram above, numbered two and three, shows options for rigid fastening using metal plates and wooden plates. In this case, the correct arrangement of additional elements is very important. A similar fastening method is used when rafters are connected end-to-end by trimming and adjusting their edges, as well as when installing rafters on a ridge girder.


  • Perforated metal plates are fixed to the rafters using nails, screws or bolts. To ensure rigidity of the connection, the rafters can be additionally attached to the purlin using metal corners. This type of fixation is quite strong and can be used for installing roofs with a large area and load.
  • Wooden linings are more reliable, since they work not only as fastenings, but also as a tightening of rafters among themselves.

If it is intended to make a reinforced fastening option, for a roofing covering that is heavy, the rafters are fastened with two rows of overlays, between which the ridge girder is pinched. This method of fixation rigidly fastens the rafters in the ridge area, but in this case, a sliding connection must be installed on the Mauerlat, which will avoid deformation of the system when the structure shrinks.

wood screws


  • A separate line can highlight the fastening of the rafters on the ridge with a triangular overlay, repeating.

This method of fixation provides a high degree of fastening rigidity, but if the slopes have a large area, then the rafter legs are additionally connected with ties. They are located below the ridge connection, and they are designed not only to impart rigidity to the structure, but also to remove part of the thrust load from the rafter system from the load-bearing walls.

These elements can also serve as a frame for covering the ceiling if it is planned to equip a residential or utility room in the attic.

Overlays and ties can be secured to the rafters using nails or self-tapping screws.

Fastening the rafters with a notch

This fastening method is shown in the diagram above as numbers four and five. With this approach, cuts are made on the rafters to fit the width of the ridge girder. Cutouts are made 5÷7 mm larger than the width of the purlin, since it is necessary to provide a distance for temperature and humidity expansion. The notch can be used in combination with other fasteners, for example, “overlapping”, “tongue-and-groove”, overlays and metal corners.

Hinged rafters

This method of connecting rafters is not often used in construction, although it is quite convenient to install and allows the rafter system to be balanced when the load-bearing walls shrink. In this method, you do not have to adjust the angle of the rafter legs, since it can be formed using a hinged fastening. It is fixed between the rafters at the required distance, which will depend on the slope of the roof slopes. The hinge is a bolt that fastens the rafters after installing them on the purlin at the desired angle.

Fastening rafters with nail plates

In addition to the elements mentioned above, nail plates are used to fasten the rafters at the ridge connection.

However, they can only be used when the trusses are assembled in a lying position on the ground, and are already installed ready-made on the Mauerlat, since this type of plate is fixed to the rafter legs using a special press. This process is almost impossible to carry out suspended in a vertical position.


By using this method of fastening wooden parts, you can significantly speed up the installation process, but for this you will have to purchase or rent a special press.

screwdriver

In this way, not only the rafter legs are fastened, but also other structural elements. Nail plates help to significantly save money on screws, bolts or nails, since you will have to purchase a lot of these fasteners, given the number of connecting nodes in the rafter system.


In addition to these fasteners, metal corners and brackets of the required size are used as auxiliary ones, driven into both rafters at the ridge part at once. However, it is necessary to work with staples extremely carefully, since they can easily split the rafter beam.

Splicing rafters on different types of roofs

Now, having familiarized yourself with the main methods of connecting and fastening rafter legs on a ridge, you should next consider what types of them are used for the installation of various rafter systems.

Gable roof system


Splicing of rafter legs in a gable roof system can be done:

- Butt, that is, they rest against each other, and in this case their ends are adjusted by trimming;

— With fastening to the ridge girder on both sides.

  • If the rafters are connected end-to-end, they are usually fixed together with overlays, which are screwed with self-tapping screws or bolts.

  • If the rafters are fixed to the ridge purlin, then they are fixed to it with metal corners, corner brackets or overlays, screwed using self-tapping screws.

This diagram shows a design with two runs:

1 – Rafter legs.

2 – Racks.

3 – Tightenings (crossbars).

4 – Runs.

5 – Mauerlat.

6 – Lie down.

  • The rafter legs of a gable rafter system can rest on two purlins mounted on racks, which are installed and fixed on the beams. For the spacer effect of the structure, tie rods (crossbars) are also used. All these elements firmly hold the rafter legs, removing the main load from the ridge, so the rafters can be fastened with an overlap or a tongue-and-groove connection.
  • If the rafter system is assembled without the use of a purlin, only by connecting the ends of the rafter legs end to end, then in addition they must be equipped with one or two pairs of overlays, which are secured to the rafters with nails, screws or bolts.
  • To fasten the rafter leg to the crossbar, when installing it end-to-end, side wooden or metal plates are used, and nail plates can also be used if the truss is assembled in advance.

  • If the rafter legs are made of logs, then they are fastened to the crossbar without the use of overlays. To connect, notches are made at the ends of the crossbar to ½ their thickness, then they are pressed against the rafters and fixed with nails or self-tapping screws. These rafter legs are additionally reinforced with struts. This is especially important to take into account if the distance between the load-bearing walls is more than 7000 mm.
  • Corner brackets are used for more reliable fixation of rafter legs on the ridge girder in buildings located in regions with strong winds. The brackets will help prevent possible displacements and deformations of the elements of the rafter system.

Rafters from logs are made only with securely reinforced load-bearing walls that have a large thickness, since the entire rafter system from them will turn out to be quite massive. If you plan to use this particular material for the structure, then it is recommended to make accurate calculations of the load-bearing capacity of the walls and the system itself in advance, and it would be best to entrust them to specialists.

Another point that must be taken into account when drawing up a roof design and during its installation is that the steeper the roof slopes, the stronger the reinforcing horizontal structural elements should be. And, conversely, if the roof slopes are located at a slight angle, then special attention should be paid to the strength of the vertical supporting elements of the rafter system.

Hip and half-hip roof

There are two similar designs - this and the half-hip rafter system. They differ in the configuration of the end slopes: if in the first there are two full hip slopes, from the ridge to the level of the cornice, then in the second the slope ends above the level of the cornice or is crowned on top with a small triangular vertical pediment.

Fastening the rafters in the ridge girder in both structures has its own characteristics, somewhat different from a conventional gable roof. The installation of these rafter systems is complicated by additional elements that form the hips - slanted legs or diagonal rafters. In addition, in addition to the usual rafter legs, which in this design are called central and intermediate, shortened ones (springs) are installed parallel to them.


If a hip roof is chosen, the size of the ridge will be less than the length of the building. According to the “classical” scheme, with equal steepness angles of the side and hip slopes, the length of the ridge will decrease by the width of the building. The cornice side of the side slopes will be equal to the length of the wall without taking into account the overhangs. Thus, the side slopes will have a trapezoidal shape, and the end hips will have a triangular shape.

In such roofs, the installation of a ridge girder (console) differs from the standard design, since the load on it will be much higher than in a conventional rafter system with two slopes.

The support posts to which the purlin will be attached must be installed on a support laid and secured to a solid interior partition or to powerful floor beams. The rafter leg closest to the hip in this design is fixed on the purlin, with a distance from the edge of 150÷200 mm. This distance will depend on the width of the diagonal rafters, which must be attached to this section of the purlin end-to-end with the outer rafters of the trapezoidal part of the roof. Such a connecting node is quite difficult to adjust independently, and the corners of the elements converging on it must be carefully calculated and adjusted by trimming.


The Mauerlat in hip and half-hip roof structures must be laid along the entire perimeter of the building box, representing a single, rigidly connected frame, as this is necessary to secure the hip elements and uniformly distribute all loads on the walls.

Diagonal (sloping) rafters that form the edges of the hip must have step-shaped cutouts or mounted cranial bars along their entire length on both sides. This is necessary to simplify the fastening of shortened hip rafters - Since the diagonal rafters are longer than the central ones, and they bear the maximum load, they are often made from two boards, fastening them together. Skull bars on diagonal rafters are secured with nails or self-tapping screws.

Work on the installation of hip elements is carried out in the following order:

  • The finished diagonal rafters are installed and secured by cutting to the edge of the ridge girder and to the central rafters of the gable part of the structure. The underside of the rafters is fixed exactly at the corner of the building on the mauerlat. Fastening can be done using metal corners and corner brackets.

  • The next step could be the installation of two struts, which are fixed on the rack of the main rafter system with one edge, and on the inner sides of the diagonal rafters, at a level of approximately ⅓ of the length from the top fastening, with the other. Fastening is carried out using metal corners or plates and self-tapping screws (nails).
  • Further, if there is a need for this, you should strengthen the diagonal slanted rafters from below with support posts attached to the truss. The sprengel is a beam installed diagonally at the corners of the mauerlat frame, on which the stand supporting the slanted rafters rests. These elements can be fastened with metal corners or staples.
  • The upper edge of the racks is cut at an angle equal to the slope of the diagonal rafters and secured to them with self-tapping screws. If necessary, the stand can be additionally strengthened with struts fixed on it and on the truss.
  • Then, depending on the slope of the diagonal rafters, splices are marked on them and secured by cutting into the cranial bars. In the lower part of the structure, the spigots are fixed to the Mauerlat.

Calculation and installation of a hip roof is not an easy task!

If you decide to build just such a roof, you will have to work hard on both the calculations and the preparation of the necessary structural elements. Read more about this in a special publication on our portal.

Installation of any rafter system is an extremely important undertaking, since the durability of the entire structure as a whole depends on the quality of its installation. Therefore, if you decide to do this work yourself, it is recommended to invite an experienced craftsman as an assistant, who will not allow the gross mistakes that beginners often make.

At the end of the publication, there is a short video that shows the process of adjusting and installing rafter legs.

Video: installing rafters on a gable roof structure

A prerequisite for installing layered rafters is to provide their upper part with support. In single-pitch roofs, this issue is solved simply: the walls are built at different heights, mauerlat beams are laid on them, on which rafters are in turn laid. In a gable roof, you can do the same: build the inner wall to the required height and lay the mauerlat on it. Then lay the rafters on the low external and high internal walls. However, this decision limits the layout options for the attic space, which is increasingly being used as an attic. And for ordinary attic roofs, this option is not profitable, because... requires significant financial costs for the construction of a high internal capital wall. Therefore, in the attic, the internal wall is replaced with a horizontal beam mounted on supports or supported on the opposing gables of the walls. A horizontal beam laid on a roof is called a purlin.

The name itself: purlin, suggests that this beam is “thrown” from wall to wall, although in reality, for example, in hip roofs it may be shorter. The simplest design solution for installing a ridge girder is to lay a powerful beam on the gables of the walls without any additional supports (Fig. 24.1).

Rice. 24.1. An example of installing a ridge girder, without additional supports, on the attic walls

In this case, to calculate the cross-sections of the purlins, the load acting on them must be collected from half the horizontal projection of the roof area.

In large buildings, the purlins are long and heavy; most likely, they will have to be installed by a crane. To make a purlin, finding an even beam of solid wood more than 6 m long is quite problematic, so for these purposes it is better to use a laminated beam or log. In any case, the ends of the purlins, walled up in the walls of the gables, must be treated with antiseptics and wrapped in rolled waterproofing material. The ends of solid wood beams are beveled at an angle of approximately 60° and left open; in the niche they should not rest against the wall material (Fig. 25). Bevelling the end of the beam increases the end area and promotes better moisture exchange throughout the beam. If the purlin passes through the wall, then where it rests on the wall, it is also wrapped with waterproofing material. Beams are passed through the walls for architectural reasons in order to provide an overhang of the roof over the gables, although this can also be achieved by moving the sheathing beyond the wall. Purlins passed through the wall form unloading consoles. The pressure load on the console tries to bend the girder upward, and the load acting on the span tries to bend it downward. Thus, the total deflection of the purlin in the middle of the span becomes smaller (Fig. 24.2).


rice. 24.2. Run with consoles

If you use a log as a purlin, then it is not necessary to cut it into two edges; it is enough to trim it at the place where the rafters support and at the place where the purlin rests on the walls. It is not advisable to make long purlins made of solid wood; they are designed for strength and deflection; however, they can bend under their own weight. It is better to replace them with construction trusses.

The cross section of the purlin is selected according to calculations based on the first and second limit states - for destruction and for deflection. A beam working in bending must meet the following conditions.

1. The internal stress that arises in it during bending from the application of an external load should not exceed the design bending resistance of wood:

σ = M/W ≤ R bend, (1)

where σ - internal stress, kg/cm²; M - maximum bending moment, kg×m (kg×100cm); W - moment of resistance of the section of the rafter leg to bending W = bh²/6, cm³; R bend - the calculated bending resistance of wood, kg/cm² (taken according to the table SNiP II-25-80 “Wooden structures” or according to the table on the website page);

2. The amount of deflection of the beam should not exceed the normalized deflection:

f = 5qL⁴/384EI ≤ f nor, (2)

where E is the modulus of elasticity of wood, for spruce and pine it is 100,000 kg/cm²; I is the moment of inertia (a measure of the inertia of a body during bending), for a rectangular section equal to bh³/12 (b and h are the width and height of the beam section), cm⁴; f nor - the normalized deflection of wooden rafters and purlins is L/200 (1/200 of the length of the checked beam span L), cm, sheathing bars and cantilever beams - L/150, load-bearing elements of valleys - L/400.

First, the bending moments M (kg × cm) are calculated. If the calculation diagram shows several moments, then all are calculated and the largest is selected. Further, by means of simple mathematical transformations of formula (1), which we omit, we obtain that the dimensions of the beam section can be found by specifying one of its parameters. For example, arbitrarily setting the thickness of the beam from which the beam will be made, we find its height using formula (3):

h = √6W/b , (3)

where b (cm) is the width of the beam section; W (cm³) - the moment of resistance of the beam to bending, calculated by the formula: W = M/R bend (where M (kg × cm) is the maximum bending moment, and R bend is the bending resistance of the wood, for spruce and pine R bend = 130 kg /cm²).

Alternatively, you can arbitrarily set the height of the beam and find its width:

b = 6W/h²

After this, the beam with the calculated parameters of width and height according to formula (2) is checked for deflection. Here it is necessary to focus your attention: in terms of load-bearing capacity, the rafter is calculated based on the highest stress, that is, the maximum bending moment, and the section that is located on the longest span is checked for deflection, that is, on the section where the greatest distance between the supports is. The deflection for all: one-, two- and three-span beams is easiest to check using formula (2), that is, as for single-span beams. For two- and three-span continuous beams, such a deflection test will show a slightly incorrect result (slightly larger than it actually will be), but this will only increase the safety factor of the beam. For a more accurate calculation, you need to use deflection formulas for the corresponding design scheme. For example, such a formula is shown in Figure 25. But let us repeat once again that it is better to include a certain safety factor in the calculation and calculate the deflection using a simple formula (2) at a distance L equal to the largest span between supports, than to find a formula corresponding to the design loading scheme. And one more thing you need to pay attention to is that according to the old SNiP 2.01.07-85, both calculations (for bearing capacity and for deflection) were carried out for the same load. The new SNiP 2.01.07-85 states that the snow load for calculating deflection must be taken with a coefficient of 0.7.

rice. 25. Example of the location of purlins on a T-shaped roof

If, after checking the beam for deflection, it is no more than L/200 in the longest section, then the section is left as it turned out. If the deflection is greater than the standard one, we increase the height of the beam or place additional supports under it, but the cross-section must be recalculated again according to the appropriate design scheme (taking into account the introduced supports).

The most difficult thing in this calculation is not to get confused in the units of measurement (in converting meters to centimeters), but everything else... Multiplying and dividing several numbers on a calculator does not require much knowledge.

Ultimately, only two numbers will appear: the width and height of the purlins required for a given load, which are rounded up to the nearest whole number.

If a log is used instead of a beam (solid, glued or assembled on an MZP), then it should be taken into account that when working in bending, due to the preservation of the fibers, the load-bearing capacity of the log is higher than that of the timber and amounts to 160 kg/cm².

The moment of inertia and resistance of a circular cross-section is determined by the formulas: I = 0.04909d⁴; W = 0.09817d³, where d is the diameter of the log at the top, cm.

Moments of resistance and inertia of a hewn log:
for one edge, equal to I = 0.04758d⁴, W = 0.09593d³, for two edges - I = 0.04611d⁴; W = 0.09781d³, with a panel width of d/3;
for one edge, equal to I = 0.04415d⁴, W = 0.09077d³, for two edges - I = 0.03949d⁴; W = 0.09120d³, with a panel width of d/2.

The height of the purlins and rafters, depending on the loads and the architectural design of the roof, can be very diverse. In addition, the forces pressing on the walls, especially when it comes to purlins, reach large values, so the roof, like everything else, must be designed in advance, even before the house is built. For example, in the layout of a house, you can introduce an internal load-bearing wall and relieve the purlins, or make capitals on the gables of the walls, put slopes under the purlins and thereby reduce their deflection. Otherwise, it will be quite difficult to connect purlins of different heights to each other and to coordinate the elevations with the gables of the walls.

When using long and heavy runs, you can use the so-called “construction lift”. This is the manufacture of a beam in the form of a rocker arm. The height of the “rocker arm” is made equal to the standard deflection of the purlin. The loaded beam will bend and become level. The method came to us from our ancestors. In log houses, when laying mats and beams (beams), they undercut the logs from below, along the entire length, making the undercut deeper in the middle part, and, if necessary, undercut the edges of the beams from above. Over time, the rocker-shaped beams sagged under their own weight and became straight. This technological technique is used quite often, for example, prestressed reinforced concrete structures are made. In everyday life, you simply do not notice this, since the structures bend, and the already small construction rise becomes completely invisible to the eye. To reduce the deflection of the beam, you can also introduce additional struts under it. If it is impossible to install struts or make a “construction lift,” you can increase the rigidity of the beam by changing its section: to a T-beam, I-beam or lattice - a truss with parallel chords, or change the cross-section by placing cantilever beams under the supports, that is, making its bottom in the form of an imperfect arch.

The support of the purlins on the wall is ensured by a transverse side support and must be designed for wood compression. In most cases, it is enough to provide the required depth of support and place a wooden lining under the block on two layers of roofing felt (waterproofing material, etc.). However, it is still necessary to carry out a verification calculation of wood for crushing. If the support does not provide the required area at which collapse will not occur, the area of ​​the wooden pad must be increased, and its height should distribute the load at an angle of 45°. The crushing stress is calculated using the formula:

N/F cm ≤ R c.90° ,

where N is the pressure force on the support, kg; F cm - crushing area, cm²; R cm90 - calculated resistance to wood crushing across the grain (for pine and spruce R cm90 = 30 kg/cm²).

It is necessary to pay special attention to the wall under the support of the ridge girder. If there is a window below, then from the top of the lintel to the bottom of the purlin there must be at least 6 rows of reinforced masonry, otherwise reinforced reinforced concrete lintels must be laid above the window along the inside of the pediment. If the layout of the house allows, the ridge purlins should not be made long and heavy; it is better to divide them into two single-span purlins or leave one and add a support under it. For example, the layout of the house shown in Figure 25 involves installing a partition in the room under the second purlin. This means that you can install a truss truss in the partition and unload the ridge girder, and then hide the truss with sheathing, say, plasterboard.


rice. 26. Rafterless roof

Another way to unload ridge purlins is that you can simply increase the number of stacked purlins, for example, install one or two unloading purlins along the roof slopes. With a significant increase in the number of beams, the question arises: why do we need rafters here at all? The sheathing can be done directly along the purlins. This is true. Such roofs are called rafterless (Fig. 26). However, in attic insulated roofs the issue of drying the insulation becomes acute, so something like rafters will still have to be made. To ensure air ventilation, it will be necessary to fill the purlins with wooden blocks, for example, 50×50 or 40×50 mm, along the slopes (in the same direction as the rafters are laid), thereby providing an air outlet with a height of 50 or 40 mm.

If you follow the wording, the purlin is a load-bearing beam that rests on the wall at both ends. In most cases, the ridge rests on two pediments, but sometimes this formulation does not entirely correspond to reality. So, in hip roofs the ridge does not rest on the walls. The simplest option is a beam laid on the gables without the use of supports. In any case, it is necessary to correctly determine the cross-section of the ridge girder.

To calculate the cross-section of the ridge girder, it is necessary to sum up the loads from half the roof, or rather, from its horizontal projection. The dimensions of the run depend on its length and the dimensions of the building. In a large building, the purlin will be so powerful and heavy that installation will require the use of a crane. However, it is very difficult to find an even, solid beam longer than 6 meters, so to make such a ridge it is better to take an ordinary log or a laminated beam.

In this case, the ends of the ridge element, which will rest on the wall and are actually walled up in it, must be treated with antiseptics and wrapped in roofing felt or roofing felt to protect it from rotting. If an all-wood beam is used, then its end must be cut at an angle of 60 degrees and left open, that is, this end should not come into contact with the wall material. This measure is needed in order to increase the area of ​​the end, which will improve moisture exchange in the wood.

If the ridge girder will pass through the entire wall, then that part of it that is in contact with the wall should also be treated with an antiseptic and wrapped with rolled material. Such an overhang of the ridge outside the wall allows you to form an unloading console. If in the middle of the ridge the load from the roof tries to bend the beam down, then on the consoles the pressing force promotes deflection in the opposite direction, thereby reducing the deflection of the purlin in the middle part.

Important: even if the cross-section of a long solid wood purlin is chosen correctly and it is suitable for deflection strength, the beam can bend under its own weight. Therefore, instead of such a long wooden ridge, it is better to use a construction truss.

Section calculation

To select the cross-section of a ridge beam, it is necessary to carry out a calculation based on two indicators:

  • for deflection;
  • and calculate the fracture strength.
  1. First, you need to determine the internal stress that occurs in the beam when bending under the influence of an external load. This value should not be greater than the calculated bending resistance of the material, which can be found in the table or in SNiP number II-25-80. We find the internal stress using the formula: Σ = M:W, where:
  • Σ is the desired value, which is determined in kg per cm²;
  • M – maximum bending moment (kg X m);
  • W is the moment of resistance to deflection at the selected rafter section (found by the formula bh²: 6).
  1. The deflection of the purlin must be compared with the normalized value, which is equal to L/200. He should not exceed it. The deflection of the beam is found by the formula f = 5qL³L:384EJ, where:
  • J is the moment of inertia, which is determined by the formula bh³:12, where h and b are the dimensions of the purlin section;
  • E – the value of the elastic modulus (for coniferous wood it is equal to 100 thousand kg/cm²).

First you need to calculate the bending moment. If there are several of them on the beam diagram, then after the calculation the largest one is selected. Next, to determine the dimensions of the beam section, we can arbitrarily set the beam width parameter and then determine its required height using the formula: h = √¯(6W:b), where:

  • b is the beam width we set in cm;
  • W is the bending resistance of the run, the value is determined by the formula: W = M/130, where M is the largest bending moment.

You can do the opposite, set an arbitrary width of the purlin and calculate its height using the formula b = 6W:h². After you calculate the dimensions of the purlin section, it must be checked for deflection using the formula from point 2.

Attention! It is better to include a small margin of safety in the calculated deflection value.

When the ridge beam is designed for deflection, it is necessary to compare this value with the value L:200. If the deflection in the longest section does not exceed this value, then the section of the beam is left as it turned out. Otherwise, it is necessary to increase the height of the run or use additional supports from below. In the latter case, the resulting section must be double-checked by again performing the calculation taking into account the supports used.

The resulting values ​​for the width and height of the ridge must be rounded up. In principle, this calculation is not difficult to perform. The most important thing is to indicate the values ​​in the required units of measurement, that is, do not get confused when converting meters to centimeters and back.

The rafter system is the basis of your future roof, so its construction must be taken very seriously. Before you start work, you need to sketch out a rough plan of the system for yourself in order to understand what the type of overall structure will be and what functions its individual elements perform.

In order to calculate the parameters and technical characteristics of the rafter system for large objects, it is best to resort to the services of professionals. If your roof is intended for a private building of a relatively small size (house area up to 100 m2), then you can perform the installation using the materials below.

The first step is to determine the angle of inclination of the slopes. Typically, average statistical calculations are based on the amount of materials, which has a very good effect on the material component of the issue; it is generally accepted that the smaller the angle of inclination, the more profitable and cheaper the construction will be. In fact, it is necessary to choose the angle of inclination from two main indicators - wind loads and the weight of precipitation (particularly in winter), as you can see, the issue of prices in the technical parameters is not usually taken into account. The universal tilt angle for our climate is 45-50 degrees; with such parameters, the strength indicators against loads, both wind and those that can be caused by precipitation pressure, are maximally balanced. Sometimes it happens that there is about 180 kg of snow per square meter of roof. In addition, the financial component will also be at an average level, which is much better than saving money by reducing the angle of inclination, but subsequently overpaying two prices for eliminating defects that will be caused by the above-mentioned factors.

Tree selection

For the rafter part, two parameters are important - strength and lightness of the structure, so ordinary pine is suitable for installation. It is often used for such structures, since it has these two qualities, plus it has a favorable price compared to noble wood. It is necessary to use a first grade board, measuring 150-200x50x6000 mm, and we will also need timber with a cross-section of 200x200 mm.

An important technical point is the moisture content of the wood. A freshly cut tree has a 50% moisture coefficient; such a tree cannot be mounted, since if it dries out in a state of tension, it may become unstable, it will bend and crack in the places where the knots are located. It is necessary to purchase material with 15-20 percent moisture content.

When purchasing, check that all boards are smooth and free of rot; the strength and durability of the structure depends on this.

When the tree is delivered to your construction site, it must be treated with antiseptic preparations and laid in a maximally ventilated area. Laying the wood must be done in a certain way: first we lay three or four transverse slats, lay boards on them lengthwise, so that there is a distance of 0.5-1 cm between each board, then again a row of transverse slats and a row of boards.

Thanks to this, we will create an air space between each unit of lumber; they will be ventilated under the right conditions, which will allow us to avoid rotting and moisture accumulation.

We install the ridge beam

A ridge beam is a central top beam that is designed to transfer the total weight of the roof evenly to the gables, distributing the pressure area along the entire side perimeter. Installing timber is a very complex process. First of all, let's decide on its length. As a rule, according to the plan, there are small canopies on the sides of the roof (from 0.5 to 1.5 m), the ridge beam must lie exactly along this length with all the protrusions outside the gables. On concrete bases, in places of contact with the timber, we lay pieces of roofing felt so that the wood does not touch the pediment directly - only through the waterproofing. We bend the roofing material around the beam, drill into the sides and insert two pieces of 12th reinforcement, 0.4 m each. We do not drill the timber itself to avoid cracks.

Extended beam

Very rarely is the standard 6 meters enough for a “ridge”. In most cases, this length has to be increased. The extension takes place at the installation site, otherwise the spliced ​​beam will be very difficult to lift up and install. The joining point of the beam must be selected in such a way that it is as close as possible to some partition or other point at which a temporary vertical support can be placed. For vertical support, we measure and cut a board, on the sides of which we nail two small boards, so we get something like a wooden fork, between the teeth of which there will be a joint of the ridge beam. We pull a thread from the top side of the ridge, which will serve as a level before we fasten the beam together. They need to be fastened with two one and a half meter sections of board, the joining sections are located exclusively on the sides, in this case the load will be applied to the tree in the right direction, reducing the risk of a break at the joint. The boards are fastened with nails, since if you try to organize bolted connections, the timber may develop a number of cracks when drilling.

Mauerlat

This element is used to connect the rafters to the longitudinal bases of the load-bearing wall, for point distribution of the load of the entire structure. It must be laid using roofing felt (as in the case of a ridge). Choose the smoothest boards; they should fit as closely as possible to the wall surface. The Mauerlat is fixed using anchor bolts 0.2 m long. The points where the anchors will be placed must be calculated in advance; their location should be in the spaces between the future rafter boards, so that the anchor caps do not interfere with our further fastening of the following elements.

If the standard length of the board is not enough, feel free to pick up the boards and fasten them in the same way as the joint between the boards of the Mauerlat will be organized - it doesn’t matter, the main thing is that they fit tightly to the concrete.

Don't forget to place the Mauerlat in short sections behind the gables, where you have planned roof peaks.

Construction and installation of rafters

The first step is to decide on the number of rafters; to do this, take the total length of the roof and divide by approximately 1.2-1.4 m, after we get a whole number, divide the length of the roof by it. An integer is the number of rafters on one side, dividing the length by this number will give us a more accurate step between them, for example, if the roof length is 9 meters:

  • 9 m / 1.3 m = 6.92(rounded up) = 7 - number of rafters;
  • 9 m / 7 = 1.28 m- step between rafters.

We multiply the number of rafters by two and again by two, thanks to these calculations we will get the total number of boards that will need to be used to make the structure.

The next step is to cut the boards to the angle of the roof. To do this, on one side of the board the perpendicular between the cut and the longitudinal part must be shifted down the required number of degrees. With the help of a protractor and a pencil, anyone can perform this procedure. Next, we cut the board along the intended line, we will get a template according to which we will trim all the other boards.

First, we install the outer rafters, which are located inside the area between the gables. The rafters are installed at two levels, the first at the ridge, the second near the mauerlat. The marking of the step between the rafters must be done both at the top and at the bottom. This line is the middle of the rafters; the design of one rafter consists of two boards, the distance between them is 50 mm.

We cut 9 boards 30 cm long and fasten them on the ridge beam clearly according to the step markings. Fastening is done using self-tapping screws and angles; the board should lie on top and perpendicular to the ridge. These segments will serve as a connecting link for attaching two opposite rafters.

In a similar way, we attach 9 pieces on each side to the mauerlat, only the length of the board should be 20 cm, and it should be located vertically, this node will be used to fasten the lower sides of the rafters.

Now you can begin the main procedures. On each upper segment (30 centimeters) it is necessary to draw a middle vertical line; it will act as a guide where the joining of two boards cut at an angle takes place. Installation of rafters begins with the first board being aligned in the center from above and nailed to a 30-centimeter section. Then a second board is nailed on the other side. It is necessary to ensure that the boards are at the same horizontal level; for this it is necessary to undermine the board that is planted below and raise it to the level of the second board, fixing it on a nail to the connecting jumper. It is highly not recommended to make cuts in the ridge beams. From below, to level the level between the boards, the opposite procedure is performed; the board, which turns out to be slightly higher, is sunk into the Mauerlat; for this it is necessary to gouge out a small groove using a chisel.

After the boards are adjusted to the level, it is necessary to tighten the lower part of the rafters with two nails and make two bolted connections, one at the top, the other at the bottom, in the places where the boards are attached to the nails. The bolted connection must be through three boards.

After this, we get an almost finished rafter, which needs to be strengthened to give it rigidity. Let's conditionally divide the length of the rafter into four parts; you can sketch out the markings with a pencil. At the junction of the first and second quarters, we fasten a 60-centimeter section between the boards to tighten the rafters. We use nails as fastening materials. We perform a similar procedure at the junction of the third and fourth quarters.

After the four rafters are mounted, we have formed two extreme triangles; at the bases and at the top, it is necessary to pull threads along the entire roof, which we will use as guides to adjust the level of all diagonally located elements.

After the side rafters, the central part is mounted, now you can knock out the support, which is located at the junction of the ridge beam, we no longer need it, at this stage the structure already has a sufficient margin of safety. Next, all other rafters are placed, one section on each side in a checkerboard pattern, to evenly distribute the loads. At the top, at the joints of opposite rafters, it is necessary to further strengthen the connections; for this we use connecting plates and self-tapping screws.

When all the rafter sections are in place, it is necessary to cut off with a hand saw all the corners that extend beyond the level of the rafters, in particular the corners of the connecting boards on the timber and on the mauerlat.

Installation of bows

The bow is a connecting board that is located approximately at the level of the midline of the rafter triangle. It serves to reduce the load on the sides of the roof; thanks to the bows, the likelihood of the roof sagging under the weight of precipitation and the likelihood of vibrations under wind loads are greatly reduced.

In our case, the height of the ridge beam is a little more than 4 meters, which means that the arrangement of the bows can be made strictly in the center, thus all loads will be distributed evenly, plus the height of the attic ceiling will be relatively normal and there will be no obstacles for moving a person of average height in it.

As in the case of rafters, the first bows are attached to the sides, after which two threads are pulled, they will help us maintain the level. After this, the central bow and all the others are attached. Bows are not needed on the outer rafter triangles, this will spoil the appearance of the roof, and besides, there are very light loads there, so from a technical point of view this step is not required.

One side of the bow is inserted into the middle of the rafter and placed on a nail, the second side, after maintaining a horizontal level, is also placed on a nail, then we make two bolted connections. It is very important to stay level at this stage, since the bow is not only a spacer, but also the basis of the ceiling of an attic or attic room.

In fact, this technology is very simple, no matter how complex it may seem at first glance. Armed with a sheet of paper and a pencil, draw the roof step by step, as indicated in the article, then the whole puzzle will form one accessible and elementary picture.

Using a standard set of construction tools, two people can build such a roof in 5-6 working days.

Evgeniy Ilyenko, rmnt.ru

The ridge beam is the top crossbar to which the rafters in the roof are attached. Installing ridge beams is considered a special skill in the work of builders: they must make a special calculation of the dimensions of the room, the mounting location, and the attic.

The ridge wooden beam and the rafters attached to it are designed to perform the following tasks during housing construction:

  1. Create a stable structure of the rafter system.
  2. Evenly distribute the pressure force and area along the lateral perimeters.
  3. Correctly distribute the weight of the roof onto the gables.
  4. Maintaining the geometry of a roof whose length is more than 4.5 m. This allows you to install rafters without using a template. If the roof dimensions are large, then a rafter beam (upper part) is placed on the ridge wooden beam, and the lower one is attached to the mauerlat.

An important condition for installing a ridge beam is to calculate the correct cross-section of such a support, which will make it possible to create a stable structure.


Let's figure out how to calculate and fasten the timber. The cross section of the run is calculated very simply: all the load data from the horizontal projection of the roof are added up. The dimensions of the ridge beam depend on 2 main parameters:
  1. Timber runs.
  2. Dimensions of the building.

The calculation of the beam parameters provides that large buildings require a powerful, heavy and rather weighty girder. But it is worth considering that such dimensions of the ridge beam will require the use of a crane. The average length of a regular beam is approximately 6 m, so to make a larger purlin you will need to look for wood or a so-called laminated beam.

The fixed ends of the ridge, pre-treated with an antiseptic, rest against the wall into which they are embedded. Additional treatment is carried out with roofing felt and roofing felt, which perfectly protects the wood from rotting. A solid wood beam is installed differently:

  1. The end is cut at an angle of 60°.
  2. The ends are left open so that the ends do not touch the walls.

As a result, when building a house, 2 problems are solved at once. Firstly, the end area becomes larger. Secondly, moisture exchange processes are normalized.

Then they calculate the dimensions of the ridge beam, which must be installed in the wall and pass through it; contact with the wall must be taken into account. Therefore, the end of the run must be well treated with an antiseptic and wrapped in rolled material. A similar design is used to make an unloading console.

When choosing the right section for a solid wooden beam, you need to take into account that the beam in the ridge can bend at any time under the weight of its own weight. Experienced builders recommend installing a construction truss so that the fixed wooden ridge beam does not break.

Calculation of the cross section of a ridge beam


Calculation of the cross-section requires taking into account the following parameters, which will be used to calculate the required size:

  • deflection data;
  • strength to destruction.

To determine the cross section, it is necessary to apply special formulas in which each indicator is important. A separate calculation determines the following data:

  1. Internal stress (Σ = M:W).
  2. Purlin deflection (according to the formula f = 5qL³L:384EJ).
  3. The dimensions of the beam section are determined by the formula h = √¯(6W:b).

The data for each formula is listed below:

Σ = M:W (definition of internal stress), where Σ is the quantity to be found. M is the maximum bending moment, which is calculated in kg/m. W is the deflection resistance of the established section.

Calculation of the deflection of the purlin is carried out using other data that must be substituted into the formula f = 5qL³L:384EJ. The letter J means the moment of inertia, to obtain which you need to know the dimensions of the purlin section (height and width, denoted by the letters h and b). Then the exponent h needs to be cubed and multiplied by b. The resulting value is divided by 12. Parameter E is the elasticity of the modulus, which is taken into account and is individual for each type of wood.

The bending moment must be calculated using the formula h = √¯(6W:b), where b is the width of the beam in centimeters, W is the bending resistance of the purlin. You can get W by dividing M (the largest bending moment) by 130.

The width and height values ​​obtained after calculation must be rounded upward. If a builder is afraid of making a mistake, you need to contact specialists who will calculate the parameters and determine what the beam and girder to be fixed should be.

Installation of ridge beams

Let's look at how to attach ridge bars. They are made only from high-quality lumber, which is due to the importance of the structure, which must perform the functions of long-term and reliable operation, bear the load, and be safe for the residents of the building. It is important that the purlin does not increase the weight of the roof, otherwise the strength of the structure will be in question. The rafters must serve for a long time, fulfilling their assigned functions. For this purpose, pine lumber with a cross-section of 20x20 cm is often used for ridge beams.

The fastening of the rafters to the ridge beam is selected depending on the type of building: residential or commercial. Depending on this, the material of the ridge, its cross-section and dimensions will be selected. For example, for a bathhouse, well-dried larch is usually used, which is heavier in weight and more resistant to stress. Larch also copes well with steam, retains heat and holds tiles. Residential buildings are built from pine, since the roof is usually covered with so-called flexible tiles.

Larch is used to make timber if the house will be covered with heavy tiles, which require a strong and strong building frame structure. It is important that the rafters not only support the roof itself, but also do not become extra weight for the walls. They must hold the purlins perfectly and not bend under them.

In order to give the rafters a central support, you need to install a beam. Its ends will rest against parallel load-bearing walls. Correct installation of such a structure requires calculation of data such as:

  1. The average annual amount of precipitation that falls in a particular area.
  2. Whether there are strong winds in the region or not.
  3. Design width of the house.

Ridge beams allow you to avoid such processes in the construction of a house as hammering nails or drilling. As a result, it is possible to avoid the formation of cracks, maintain the integrity of the timber and ensure the reliability of the entire rafter system.

A gable roof also requires the use of a ridge purlin, which subsequently serves as the roof ridge. In order to build a residential building measuring 6x6 m, it is recommended to take a purlin made of logs or solid timber. The purlin will rest on 2 gables and no supports will be needed. If the length of the house is more than 6 m, then it is allowed to use construction trusses and a composite ridge girder. It is important that the timber lies on the external gables.

Fastening the ridge beams is carried out using different methods, which allows you to connect the beams in the desired way. The main purpose of each connection is to make the structure strong and reliable. Modern technologies make it possible to connect beams together without using any additional materials for insulation. If the design documentation is drawn up correctly, the house will not only be strong and able to support the roof, but will also become environmentally friendly and reliable for habitation.