The strength and reliability of its entire structure directly depends on how competently the roof supporting system is mounted. The rafters are its main elements.
Completely the system includes rafter legs that expand and support all additional elements (braces, crossbars, struts, support braces and struts, side girders). At the top of the ridge beam, these legs rafters are connected, their lower edges usually rest on the Mauerlat fixed to the supporting side walls .
Of all the listed elements, the highest load falls on the Mauerlat, therefore, a strong powerful bar is used for its manufacture.
What section should it be?
It is determined by the size and weight of the rafter system, but most often its size is from 150 to 150 mm and, depending on these factors, up to 200 to 200 mm.
This element contributes to the even distribution of the mass of the entire roof-roof structure on the walls of the dwelling.
Rafters to the Mauerlat can be attached in different ways. The choice of a particular method depends on the type of system ( hanging or inclined ), on its massiveness and complexity, on the total amount of loads that will act on the entire roof structure.
First, note that there are two main types of attachment to the Mauerlat: sliding and rigid.
In sliders, the mount itself consists of a pair of separate elements, one of which is able to move freely relative to the other.
By their design, they are closed and open.
This is a corner, on one side of which a special eyelet is made in the form of a slit, and on the other side it is attached to the Mauerlat. A metal loop is fixed in the slotted eyelet, equipped with holes with which it is attached to the rafter. The loose, free vertical side of the corner allows the rafter to move slightly if necessary, without loading or deforming the walls with its effect.
The principle of the open attachment device is generally the same. The difference is that no loop is inserted into the eyelet. After installation, the upper part of the angle shelf is folded down to secure the connection.
Rigid mounts are available in a much larger number of types. The most suitable one is chosen based on various factors: the severity and massiveness of the wooden components, the selected method of installing the rafters.
This includes all kinds of different-sized metal corners, LK mounts, holding the rafters installed with a saw.
In this case, the latter are not damaged by nails or fixing screws.
LK mounts are made in different sizes, and you can easily choose the optimal one for any thickness of the board or bar. Regardless of the size of such fasteners, metal of the same thickness is always used for their manufacture - 2 mm. It's easy to understand them - different sizes of fasteners are indicated in different ways.
It should be noted that such fasteners are convenient not only for fixing the Mauerlat and rafters. They are also suitable for fixing the Mauerlat with floor beams. The main advantage of such fasteners is maximum reliability and rigidity of joining wooden parts.
The rafters with a saw cut on the Mauerlat must be fixed on both sides. This is the only way to guarantee the required rigidity.
Angles are also available that serve to fix the rafters without cuts. They have a large shelf height; you need more screws to fix them. They are made of metal in 2; 2.5 or even 3 mm thick.
Another interesting option for attaching rafters.
They are installed between two boards, sawn at a given angle, and at the bottom they are additionally fixed with LK-fasteners or metal corners. This fixation provides excellent rigidity and high reliability. This method is good when you need to fix the rafter at a certain angle, slightly lifting it above the Mauerlat plane, while fixing it to the outer vertical side.
Another method is used when the Mauerlat is made of a not very large bar. Such a bar can be reinforced with wood pads of various thicknesses.
Sections of boards are attached with nails or self-tapping screws to the Mauerlat in those places where the rafter legs will stand.
Then special cuts of the required depth and shape are made in the rafters. You can securely attach the rafter legs to the wall using strong steel wire, which is securely attached to a steel crutch that is securely driven in.
The rafters can be stapled to the Mauerlat. This method has been used for a long time and is considered to be quite common.
If everything is done correctly, such a rafter system will serve for many years. Staples come in different sizes and can also be driven in different places.
The perforated tape TM can be considered an auxiliary fastener. It is used if additional fixation of the fastening unit is required to strengthen it. In some cases, it turns out to be irreplaceable.
The type of rafter system is selected based on how the load-bearing walls of the structure are located. Each such system involves its own additional elements, tightening or retaining.
What are the differences between the system with the so-called inclined rafters? In addition to the main load-bearing walls, it has one more (or even more than one) anchor point. Thanks to this, most of the load is removed from the walls.
As additional supporting fasteners, side "headstock" and stands are used, which are fixed on the floor beams and support the ridge.
At the same time, the beams themselves are also braces for the structure, making it easier for the load-bearing walls to load the rafter system.
Such rafters are usually attached to the Mauerlat with sliding joints that can move when the walls are deformed or shrink, protecting the roof structure from damage.
This is especially important for only erected buildings, since any new building, under the influence of temperature fluctuations and ground movements, will certainly shrink.
Which rafters are called hanging rafters?
Those that, apart from two side walls, have no other supports ..
. In other words, they seem to hang over the inner space of the building itself.
It is clear that in this case, the main load from the entire roofing structure falls on Mauerlat .
Hanging rafters are attached to the Mauerlat exclusively with rigid connections that completely limit the possibility of movement: after all, the frame structure has only a couple of support points. By its structure, the system of hanging rafters is considered to be a spacer - that is why such significant pressure falls on the walls.
In order to remove some part of the load from the walls, special additional elements are used (tie bars, struts and "headstock"). They pull the entire system to the ridge bar, distributing the load on the walls evenly. In parallel to the floor beams, crossbars are installed, with the help of which the rafters are pulled together.
Such additional devices provide the structure with greater reliability.
In order for the connections of such important elements to be reliable enough, it is important to follow the rules specially developed for this:
This is a rigid attachment method and can be used for hanging rafters.
If the Mauerlat is not used and the rafters are attached directly to the floor beams, a point distribution of the load from the weight of the entire roof occurs.
For this, elongated beams are used, which should protrude 40 cm beyond the line of the walls. A string is stretched across the beams - this is how an equal angle is observed when fastening. This string will serve as a guide when the grooves begin to cut under the soles of the rafters. How are beams and rafters fastened? There are three popular methods:
The number of teeth required (two or one) depends on the angle of inclination of the rafter sole. The rafter ends are inserted into the grooves, additionally fixing the rafters on the beams with steel corners or bolted connections. A single tooth is sufficient if the attachment to the beam is done using a cut.
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Posted By: Work Style |12, Nov 2020
Posted By: Work Style |12, Nov 2020
Posted By: Work Style |06, Nov 2020
Posted By: Work Style |06, Nov 2020
Posted By: Work Style |13, Nov 2020