Knots of the rafter system. Metal roof rafters - design and installation features. Gable roof rafter system for small houses

03.11.2019

We embroider a Slavic amulet with a cross

Name Vitaly - meaning, fate and character

The rafter system is the frame of the roof of the house, which carries and evenly distributes the weight roofing pie, sometimes reaching up to 500 kg/m2. The reliability of this unique frame depends on three factors: the accuracy of the calculation, on the basis of which the number and cross-section of the supporting elements are selected, the material from which it is made, as well as the correctness of the fastening technology. Knowing how to properly fasten rafters, you can significantly increase the load-bearing capacity of the frame, making it stronger and more reliable. Installation errors, on the contrary, lead to significant losses in strength and deformation of the roof. In this article we will talk about the main types and methods of fastenings with which you can qualitatively install rafters with your own hands.

The rafter frame of the roof of a house is a system of interconnected supporting elements made of wood or metal that give the structure its shape, slope, and also evenly distribute its weight between the load-bearing walls.

Its main component is the rafter legs, which are beams installed at an angle, which are connected in pairs along the slope, forming a ridge at the top point of their connection. There are two main types of rafters: Layered. Layered rafters are called supporting elements that have two points of support in the roof structure - on the ridge girder and the mauerlat. A rafter system of this type is used in structures that have one or more load-bearing walls
, on which you can “lean” the rafters. This fastening of the rafters allows you to relieve them through the use of additional vertical supports. Hanging. Hanging elements are those that have only one support point, located where the rafters are attached to the wall or mauerlat. Rafter system hanging type

Note! In most of the most popular rafter systems, the rafters are attached to the Mauerlat. Mauerlat is a massive beam or beam with a cross-section of 150x150 mm or 200x200 mm, laid along the load-bearing walls of the structure, on which the rafter legs will subsequently rest. It softens the pressure on the walls of the house and also evenly distributes the weight of the roofing pie. You can attach the Mauerlat to the upper chord of the walls using anchor bolts or embedded metal studs.

Main connecting nodes

The rafter frame is called a system because all its elements are closely interconnected and fixed, as a result of which the roof structure acquires a stable shape, rigidity and high load-bearing capacity.

Each connecting node between its parts is a vulnerable point that can easily deform under load, so all fastenings must be carried out strictly according to technology. Experienced craftsmen identify the types of connections in the roof structure: Attaching the rafters to the ridge beam. This connecting unit is typical only for layered rafter systems, in which the upper part of the rafter leg rests on a ridge purlin fixed to vertical racks
. The rafters can be attached to it using metal plates, nails or sliding slide fasteners. Fastening the rafters to the mauerlat. The most important fastening point rafter frame The junction of the mauerlat beam with the rafter legs is considered. You can fix the rafters on it using nails, metal corners
or wooden blocks. Connecting the rafters to each other. To lengthen the rafter legs if the length of the slope exceeds standard length
lumber, they are assembled from several elements connected to each other using nails, glue or metal plates. Connection of rafter legs with auxiliary supporting elements. In truss frame construction, rafters can be connected to tie rods, transoms, or struts to increase rigidity, strength, and.

bearing capacity Please note that any cuts made to attach the rafters to beams, mauerlat or other structural elements of the frame lead to a decrease in their strength, therefore experienced craftsmen

It is recommended to connect them together using corners and overlays.

Fixation methods When deciding how to attach the rafters to the mauerlat or ridge girder, you need to choose the right fastening fittings . Modern construction market huge assortment fastenings of various designs and sizes. The main criteria for choosing fasteners are the material used to make the rafters, their cross-section, as well as the type of load to which they are subjected.

There are the following methods of fastening rafters: Experienced craftsmen believe that the most reliable way to fix rafters is to use metal corners that firmly connect wooden elements

between themselves, rigidly fixing the angle between them. The corner that covers the joint between the rafter leg and the ridge beam or mauerlat serves as a kind of spacer between them.

Types of fastenings Tree - natural material , which in the process of equalizing humidity and drying gives significant shrinkage, due to which linear dimensions structures are changing. That is why experienced craftsmen recommend erecting a roof for timber and log houses a year after construction, when the shrinkage process passes from the active to the passive phase. If you fix the wooden frame elements rigidly, then after drying the roof of the house may become deformed. Therefore, to connect the rafters they use

the following types

fastenings:

Interestingly, there are several options for combinations of movable and fixed connecting nodes. The most common are rafter systems with one rigid and two sliding fasteners, which provide sufficient mobility with high strength and rigidity of the structure.

Types of fasteners
There is ongoing debate among experienced roofers as to what is the most effective way to attach rafters to floor beams and mauerlat.

Most experienced roofers agree that to fix rafter legs it is better to use galvanized rough nails, the length of which is 5-3 mm greater than the thickness of the lumber. Properly selected fasteners are the key to high-quality and long-term fixation of the roof frame, which will not be afraid of either mechanical stress or wind load.

Video instruction

Is it possible to highlight some main detail in the roof? This is unlikely to work, since here each element performs its own function. For example, rafters are a part of a roof that has slopes, which can be called a frame. It is on them that the roofing material will be laid and other elements will be attached. The final shape of the roof will depend on how the rafter system is assembled and installed. But if you do the work of creating the roof yourself, then how to attach the rafters? In fact, this is a rather complex stage of work, on which the strength, reliability, and even geometric correctness of the roof will depend.

The rafter system is a roof frame with slopes, assembled from the rafter legs themselves, as well as the mauerlat and ridge beam. Mauerlat is a support beam that is located along the perimeter of the upper part of the walls of the house, and ridge beam is installed directly in the upper part of the roof in the place where two opposite rafter legs are connected at an angle.

Design rafter system – important task, during which it is necessary to correctly calculate the wind and snow loads that will fall on the roof, as well as take into account other parameters. The first indicators will depend on in what climatic region there will be a facility under construction. Next, based on the data obtained, the thickness of the walls of the house itself (load-bearing) is calculated, and the quality and type of material for the roof itself is selected, the angle of inclination of its slopes and other points are calculated.

Attention! Shortcomings and errors made during the design can negatively affect the quality of the roof. In some cases, they can lead to rapid collapse or destruction of the roof.

The design of the rafter system may include the rafters themselves, the ties that will be located between them, purlins, additional supports - the so-called rafter legs - and other elements. The assembled rafter system usually rests on the same Mauerlat or on floor beams. Mauerlat helps to evenly distribute the load along the entire perimeter of the walls. This is the main difference between this method of fastening. If you attach the rafter system to the floor beams, that is, without installing a Mauerlat, then the main load will fall on the attachment points and not be distributed evenly over all walls.

On a note! The latter case is not an option if the walls are made of brick, which will begin to collapse over time in places experiencing maximum load. But for wooden log house This method is quite suitable.

Table. Dependence of the cross-section of rafter legs on their length and pitch.

Pitch, cm / Length, cm	300	350	400	450	500	550	600
60	4x15	4x17.5	5x15	5x15	5x17.5	5x20	5x20
90	5x15	5x17.5	5x20	7.5x17.5	7.5x17.5	7.5x20	7.5x20
110	7.5x12.5	7.5x15	7.5x17.5	7.5x17.5	7.5x20	7.5x20	10x20
140	7.5x15	7.5x17.5	7.5x20	7.5x20	7.5x20	10x20	10x20
175	10x15	7.5x20	7.5x20	10x20	10x20	10x25	10x25
215	10x15	10x17.5	10x20	10x20	10x25	10x25	-

The roofing system is a part of the roof structure from the outside, which is supported load-bearing structure. It includes sheathing and rafter system. The triangle underlying this system must be rigid and the most economical structural element, which contains fastening points for roof rafters.

The main characteristics of the rafter system components

The main fastening points of the roof truss system are shown in Fig. 1. They imply the presence of a rafter leg (mauerlat - 1), a rafter leg (ridge girder - 2), a stand (tightening - 3). The design of the rafter system is the main load-bearing element of the roof.

All roof fastening units must have sufficient strength, this should eliminate a significant degree of risk associated with roof collapse. The consequences of a mistake made when connecting elements can be the most unpredictable.

Figure 1. Main fastening units of the roof truss system: 1 – Mauerlat, 2 – ridge girder, 3 – tie-downs.

First, the rafters are installed on the Mauerlat if the building has brick walls. Similar units are provided for concrete blocks; then it is necessary to create a reinforced concrete stiffening belt, and studs must be inserted into its structure. Their location should be at a distance of 1 to 1.5 m from each other, and their diameter should be more than 14 mm. The top of the studs must be equipped with a special thread.

The Mauerlat is drilled, making holes that are necessary for fastening the elements on it. Each hole must have a size that matches the diameter of the stud, and its pitch must correspond to the distance between the studs. A nut is put on each protruding end of the stud and tightened, which ensures the strength of the connection between the Mauerlat and the wall. The rafters should be connected to the Mauerlat in such a way that their load-bearing capacity does not weaken.

Description of the main fasteners for installing the rafter system

If during the construction of a house a rounded log or beam was used, then it is not necessary to create an armored belt. produced on the top beam or on the wall log. For this purpose, connections between the Mauerlat and the rafters are used different ways cut (inset).

What fasteners are used to secure metal rafters:

Plates.
LK fasteners.
Corners.
Brackets WB.
Self-tapping screws.
Varieties of the corner of the Kyrgyz Republic.
Wire ties.
Perforated mounting tape TM.
Bolts and nuts.
Brackets WB.

If brackets are used to connect the rafters to the mauerlat, then they are not inserted into the rafters, which helps strengthen the load-bearing capacity. Usually metal brackets are produced, and the metal is galvanized and has a thickness of 0.2 cm. The brackets are reinforced with nails, anchor bolts or screws.

You can use the LK fastener to create fastening points not only for rafters with a Mauerlat, but also for other various elements, components of the roof structure. Fastening element LK is fixed to wood, like brackets, with the exception of the use of anchor types of bolts.

Assembly perforated tape allows you to strengthen connecting nodes during the construction of roofing systems. It is used not only to create stronger units, but also to strengthen elements for additional use in order to impart rigidity or strength to the system as a whole. Attach the perforated mounting tape screws or nails, therefore it is used to strengthen the structure of the rafter system of any roof, the integrity of which will not be compromised.

Using KR corners and their various modifications, the fastening points are strengthened so that they can effectively participate in connecting the mauerlat and rafters. Providing adequate strength to roof assemblies is permissible when using corners, which makes it possible to increase load-bearing characteristics roofing structure.

The use of metal connecting elements does not involve inserting corners into the roofing system. This will not cause a decrease in the load-bearing capacity of the roofing system. You can use corners for connections using screws or nails, the protrusions of which resemble a ruff.

How are the nodes connected in the ridge part?

There are three main types of fastening in the ridge parts of a roofing system:

Butt connection.
Fastening based on a ridge girder.
Overlapping ridge joint.

For the purpose of fastening, the first method is to cut off the ridge part from the upper edge at an angle that is the same as the angle of the roof slope. Then it is rested against the required rafter, which should also be cut at an angle, but on the opposite side of the roof. A special template is sometimes used to trim corners.

The nails for connecting the rafters under the ridge must be 150 mm or larger in size; you will need two of them. Each nail is driven into the rafters at the top at the appropriate angle. The sharp end of the nailed nail usually enters the cut of the rafter on opposite sides. Strengthening the ridge joint can be achieved by placing a metal plate on the side or a wooden overlay on it so that it is enough to tighten it with bolts or nails.

The connection in the second way, that is, through a ridge girder, involves strengthening the rafters on the ridge beam. The purlin is one of the additional support beams or beams, which supports the rafters. It is located parallel to the ridge or mauerlat. The method differs from the previous one in that a ridge beam is laid between the rafters, which are cut at an angle, which is a labor-intensive process, therefore this method used less often.

The more common method is similar to the first, but it differs in that the fastening is done overlapping, and the joint method is not used. The rafters should be in contact with their ends, and not with their side surfaces. The rafters should be tightened with a bolt or pin or nails. This connection is used by many masters in practice.

In general, it is possible to install rafters on a Mauerlat by creating structures for roofing rafter systems that are either spacer or non-spacer. This determines the choice of the appropriate method of connecting the Mauerlat and rafters, which can be similarly strengthened to the ridge.

The main disadvantages when installing rafter system fastening units

The problem of choosing a method for attaching the rafter system to the structure of the building is very important when creating attachment points. Often, when creating nodes, the Mauerlat serves as a support for the rafters. The Mauerlat beam is fastened “tightly” using anchor bolts to the reinforced stiffening belt.

A possible drawback is the unanchored stiffening belt, which can lead to the overturning of the mauerlat beam and disruption of the stability of the roof rafter system. The roof becomes loose and the roof slides down. Due to incorrect placement of anchor bolts or incorrectly made holes, the fastening is no longer effective.

If the nuts are screwed with overtightening onto the bolts, then the fastening unit becomes fragile and is subject to rapid destruction. To create a fastening point, twisted wire is sometimes used.

When constructing a rafter system, the safety of connections must be observed.

For example, if truss structure combined with the floor without taking into account the load-bearing capacity of the attic floor, this is the most dangerous moment that can lead to the destruction of the building.

If the tie is replaced with a precast reinforced concrete floor beam intended for bending, then the use of precast reinforced concrete beams should be effective due to their rigid fixation in reinforced belt the rigidity of the floor, which is constructed using a reinforcement cage. Its axis must go in the same direction as the acting forces.

At the same time, the presence of shortcomings in the process of creating a rafter system, which is a load-bearing wooden structure ceilings, often arises due to a misunderstanding of the functions performed by the tie and crossbar in the entire roofing system. The tie differs from the crossbar in that it is a longitudinal beam, and the crossbar is a transverse beam.

The construction of a rafter system involves the creation of a spacer system that works on the principle of divergence at the bottom of the planes, which occurs under the influence not only of their own weight, but also of the load that falls on the line of intersection of the planes, which should be prevented by a transverse beam, that is, a tightening.

When starting to install a roof, you should clarify all the points associated with making certain mistakes that arise when performing work on installing a rafter system. The construction of the roof of a house is associated with possible difficulties and shortcomings that do not allow achieving the set goal.

When designing any residential building, architects Special attention pay attention to the roof, since it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with an ordinary gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many people are more attracted to complex designs, which add special attractiveness and originality to the building. Other, more practical homeowners prefer attic structures, which can simultaneously serve as a roof and a second floor.

The basis of any roof is an individual rafter system, which has its own design features. Make a choice the required frame roofs will be much easier if you figure out in advance what types and diagrams of rafter systems used in construction practice. After receiving such information, it will become more clear how difficult such structures are to install. This is especially important to know if you plan to build the roof frame yourself.

Main functional tasks of rafter systems

When settling in pitched structures roofs, the rafter system is a frame for covering and holding the materials of the “roofing cake”. With proper installation frame structure will be created the necessary conditions for correct and non-insulated roof types, protecting walls and inner space houses from various atmospheric influences.

Roof structure is also always final architectural element exterior design of the building, supporting it with its appearance stylistic direction. However, the design features of rafter systems must first of all meet the strength and reliability requirements that the roof must meet, and only then the aesthetic criteria.

The frame of the rafter system forms the configuration and angle of inclination of the roof. These parameters largely depend on natural factors characteristic of a particular region, as well as on the desires and capabilities of the homeowner:

Precipitation in different periods of the year.
Direction and average speed winds in the area where the building will be erected.
Plans for the use of space under the roof - arranging residential or non-residential premises, or using it only as air gap for thermal insulation of rooms below.
Type of planned material roofing covering.
Financial capabilities of the homeowner.

Atmospheric precipitation and the strength of wind currents place a very sensitive load on the roof structure. For example, in regions with heavy snowfall, you should not choose a rafter system with small angle slope of the slopes, since snow masses will linger on their surface, which can lead to deformation of the frame or roofing or to leaks.

If the area where the construction will take place is famous for its winds, then it is better to choose a structure with a slight slope so that occasional sharp gusts do not disrupt individual elements roofs and roofs.

Main elements of roof structure

Parts and components of rafter systems

Depending on the chosen type of rafter system, the structural elements used can vary significantly, however, there are parts that are present in both simple and complex systems roofs

To the main elements of the rafter system pitched roof relate:

Rafter legs that form the roof slopes.
- wooden beam, fixed to the walls of the house and used to fix the lower part of the rafter legs on it.

A ridge is the junction of the frames of two slopes. It is usually the highest horizontal line of the roof and serves as the support to which the rafters are anchored. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (purlin).
Sheathing is slats or beams mounted on rafters at a certain pitch and serving as the basis for laying the selected roofing material.
Supporting elements, which include beams, purlins, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, tie individual parts into the overall design.

In addition to the mentioned design details, it may also include other elements, the functions of which are aimed at strengthening the system and optimally distributing roof loads on the walls of the building.

The rafter system is divided into several categories depending on different features of its design.

Attic space

Before we look at different types roofs, it is worth understanding what the attic space can be, since many owners successfully use it as utility and full-fledged residential premises.

The design of pitched roofs can be divided into attics and attics. The first option is called this way because the space under the roof has a small height and is used only as an air layer insulating the building on top. Such systems usually include or have several slopes, but located at a very slight angle.

An attic structure that has a sufficiently high ridge height can be used in different ways, be insulated and not insulated. Such options include an attic or gable option. If you choose a roof with a high ridge, then it is imperative to take into account wind loads in the region where the house was built.

Slope slope

To determine optimal inclination roof slopes of a future residential building, first of all you need to take a closer look at the already built low-rise neighboring houses. If they have been standing for more than one year and can withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set a goal to create an exclusive original project, unlike the nearby buildings, it is necessary to familiarize yourself with the structural and operational features various rafter systems and make the appropriate calculations.

It should be taken into account that the change in tangential and normal values of wind force depends on how large the slope of the roof slopes is - the steeper the slope angle, the higher value have normal forces and less tangent forces. If the roof is flat, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.

Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in conjunction with the wind load, since on the windward side the snow load will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will certainly accumulate, putting a large load on this area, so it should be reinforced with additional rafters.

The slope of roof slopes can vary from 10 to 60 degrees, and it must be selected not only taking into account the consolidated external load, but also depending on the roofing covering that is planned to be used. This factor is taken into account because roofing materials vary in their mass; to secure them, they require different quantity elements of the rafter system, which means the load on the walls of the house will vary, and how large it will be also depends on the angle of the roof. The characteristics of each coating in terms of resistance to moisture penetration are also important - many roofing materials in any case require one or another slope to ensure free descent storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance about how the cleaning process will be carried out and repair work on the roof.

When planning a particular angle of the roof slopes, you need to know that the fewer joints between the sheets of roofing, and the more airtight they are, the less you can make the slope of the slope, of course, if you are not planning to arrange a residential or utility room in the attic space.

If a material consisting of small elements is used to cover the roof, for example, ceramic tiles, then the slope of the slopes must be made steep enough so that water never lingers on the surface.

Considering the weight of the roofing material, you need to know that the heavier the covering, the larger the angle of the slopes should be, since in this case the load will be correctly distributed over the rafter system and load-bearing walls.

Can be used to cover the roof following materials: or profile sheet, galvanized steel, corrugated asbestos concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roof and other roofing materials. The illustration below shows the permissible slope angles for various types roofing coverings.

Basic designs of rafter systems

First of all, it is worth considering basic types rafter systems relative to the location of the walls of the house, which are used in all roof structures. Basic options They are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.

fastenings for rafters

Layered system

In buildings where internal load-bearing walls are provided, a layered rafter system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, this structure will require less materials.

For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of layered system can be arranged in three options:

In the first option, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the mauerlat. Additionally, the rafters in the lower part are fixed to the wall using wire or staples.

In the second case, the rafters in the upper part are cut at a certain angle and connected to each other using special metal plates.

The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.

In the third option, the rafters are rigidly fastened in the upper part with bars or treated boards located horizontally, parallel to each other on both sides of rafters connected at an angle, and a ridge girder is clamped between them.

In the lower part, sliding fasteners are used to secure the rafters, just as in the previous case.

It is necessary to explain why sliding fasteners are often used to secure rafters to the mauerlat. The fact is that they are able to relieve load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they are able to move without deforming general design roofing system.

This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.

However, in some cases, for layered rafters, a spacer system is used, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and to relieve the load from the walls, tie-downs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.