- Types of rafter supports on the Mauerlat
- Hanging rafters
- The connection of rafters with a Mauerlat, depending on the material and construction of the wall
- Brick walls
- Wooden walls
- Aerated concrete block walls
- The connection of the rafters with the Mauerlat, depending on the rafter structure
- Several rules for choosing a method of connecting rafters with a Mauerlat
The importance of properly attaching the rafters to the Mauerlat can hardly be overestimated. The rafter leg, resting on the Mauerlat, transfers all the load from the roof directly to the structure of the outer wall of the building. In addition, this connection should prevent a possible breakdown of the roof from strong wind loads..
For fastening structures made of wood, fasteners are used, which are made of sheet or profile steel, metric fasteners, nails, staples.
For nail connections are used: bolts, nails, rods, claw washers.
If the diameter of the nail is less than 6 mm, then for soft woods they are driven in without first drilling the socket. With diameters greater than 6 mm, in order to avoid the formation of cracks in the wood, a socket with a size of 0.9 of the nail diameter is drilled under the nail.
Brackets are used only for joining log or timber elements in the absence of the possibility of splitting the tree. It is advisable to place them in pre-drilled holes of a smaller diameter..
Types of rafter supports on the Mauerlat
Rafters can be of two types: hanging and layered. It depends on the ability to support them against the walls. Hanging rafters have one point of support on the Mauerlat, with the other end creating a ridge knot with a frontal stop of two rafters. Inclined rafters are supported on the outside on one side, and on the other – on the inner wall of the building. Hanging, not having a second point of support, create a thrust from the deflection of the rafter structure. That is why they have a puff at the bottom, which takes on the bursting forces.
The rafters are fastened directly to the Mauerlat. Most often, for this, an inset is made in the rafter legs. Its depth is provided for less than 1/4 of the height of the rafters. They are fixed on both sides with corners.
Roof rafter system: 1 – Mauerlat; 2 – perforated corner; 3 – bed; 4 – rafter leg; 5 – rack; 6 – ridge run; 7 – cross brace; 8 – waterproofing; 9 – longitudinal brace
Sometimes this fixation is carried out using staples.. The staples are driven into both the rafters and the Mauerlat.
This method of fastening the rafters and the Mauerlat is carried out using beam holders attached on both sides:
Often, three nails are driven into the rafters to increase the rigidity of the connection. One vertically and two criss-cross. Moreover, the length of the hammered part of the nail must exceed 10 diameters of the nail and 2 thicknesses of the element that the nail pierces.
Important! Due to the fact that larch is easily split, connections on nails and staples cannot be used for it..
The hanging type of rafters is used for buildings with a width of 6 to 12 meters. With the option of a hanging rafter leg, the load from the rafters is transmitted to the Mauerlat through a tightening. Here the strength of the rafters is not weakened by the tie-in device.
Hanging rafter system: 1 – Mauerlat; 2 – tightening; 3 – perforated corner; 4 – crossbar; 5 – ridge run; 6 – rafters; 7 – mounting bolts
When the length of the rafter leg is not enough to create the necessary overhang of the roof, it is cut off at the level of the Mauerlat. The overhang is made using small wooden blocks (filly).
The connection of rafters with a Mauerlat, depending on the material and construction of the wall
The design of the walls, like the material from which they are made, directly affects the way the rafters are fastened to the Mauerlat.
In brick walls, the rafter legs are attached to the Mauerlat using corners, brackets, nails, etc..
To protect against tearing off the roof in windy weather, the rafter legs are fixed through one in the wall using a twist (O 2–3 mm) of 2–3 wires to a crutch. The metal crutch is sealed in advance in the masonry 200–300 mm below the Mauerlat. All parts of the roof made of wood, concerning the brickwork, should be protected from moisture by waterproofing gaskets in 2 layers (roofing material, waterproofing, etc.).
Important! Do not completely brick or seal up the gaps between the wooden elements of the rafter supports and brick walls. They should be open but protected from moisture.
A significant difference between the pairing of rafters and Mauerlat for wooden walls is the need for a certain mobility of the rafters relative to the Mauerlat. A wooden house immediately after construction shrinks, which can disrupt the roof structure if wooden elements are rigidly attached.
Here, a movable type of attachment is used. It allows the rafter leg to have some freedom in two directions. For such connections, factory-made fasteners are used..
The Mauerlat is protected from wind loads by connecting it to the penultimate crown of a log wall or a wall made of timber. To do this, they drive the staples into the Mauerlat and the wall. In houses made of timber or logs, the last crown of the wall often serves as a mauerlat..
Aerated concrete block walls
Aerated concrete blocks do not have sufficient strength to fasten the roof to the walls. Therefore, a monolithic reinforced belt is made in them, in which metal pins are laid.
The Mauerlat is mounted on them through a pre-drilled hole and bolted to the belt. We must not forget about waterproofing between wood and concrete. Otherwise, the principle of fastening the Mauerlat and rafters remains the same.
The connection of the rafters with the Mauerlat, depending on the rafter structure
The roof rafter system can have a huge variety of options. This is ensured by fairly easy processing of wood as a building material. In general, several types of such systems can be distinguished: beams, arches, trusses and even frames.
In any particular version of the rafter roof, there are differences in the device for pairing the rafters with the Mauerlat. For small buildings (barn, garage, small country house, etc.), you can make this connection yourself, guided by the above methods of fastening.
For more critical buildings and structures, all interface elements are calculated, including metal fasteners. According to the calculation made, the material, size and number of required structural parts are selected. That is why in such cases it is better to entrust the design calculation to specialists..
Several rules for choosing a method of connecting rafters with a Mauerlat
1. The standard moisture content of wood is 12%. Freshly cut wood can have a moisture content of up to 100%. When wood shrinks, it deforms. If products that have not reached the standard moisture content are used for rafters, destruction of the integrity of the wood may occur in the rigid connection of the Mauerlat and the rafters. It is advisable to use products of standard humidity, as well as to exclude the possibility of wetting wooden parts by processing with moisture-proof coatings.
2. If part of the rafter leg is in a warm room, and part in a cold one, different temperature and humidity conditions of operation also affect the operation of the entire roof structure. In this case, it is necessary to make additional protection in places where walls or ceilings pass from biological damage to wood and exposure to moisture (treatment with special substances). Under such operating conditions, only rectangular rafters are used..
3. When trimming the rafter leg, it should be borne in mind that the length of the part that rests on the Mauerlat should be less than the height of the rafters.
4. The junction of the rafters and the Mauerlat in the stone outer walls should be insulated to protect it from freezing.
5. It is important that condensation cannot form on the metal parts of the joints. If this still happens, then the wooden part of contact with the metal must be protected from moisture (elastic gaskets, mastics, sealing tapes, roofing material, waterproofing, etc.).