The rafters are fastened to the floor beams during the construction of mansard roofs with low weight. Mounting points are as reliable as possible if you choose the right mounting option and follow the technology.
Features of the truss system
When designing a roof structure, it is necessary to choose the appropriate option for the truss system. Among others, layered and hanging rafters should be distinguished. For light roofs of an impressive area, hanging-type trusses are usually used. For them, the walls act as a support.
More solid and complex is the system with layered rafters. In them, the rafter legs have additional points of support. When erecting a roof, the truss system relies on a mauerlat, which is a structure on the longitudinal walls or installed around the perimeter of the house. This option for attaching rafters to floor beams is used if the house is being built from blocks or bricks.
If on top of the walls there is a concrete monolithicthe beam or walls are made of logs or timber, then the roof rests on a horizontal beam, and not on a Mauerlat. The beams in this case overlap the building box in the transverse direction. The simplest option for a light mansard roof is a roof frame that rests on beams.
During the design process, it is necessary to calculate the rafter legs and the thickness of the beams, taking into account the loads on the roofing system. During installation, it is necessary to ensure that the rafters are supported on the beams. Fastening rafters to floor beams without Mauerlat can only be carried out if the walls of the building can withstand impressive point loads.
In what cases is the truss system based on floor beams
If the floor beams act as a support for hanging rafters, the system creates high loads on building structures. This approach is relevant in the construction of wooden houses, because timber or logs oriented horizontally provide an even distribution of the load. But in the case of brick walls, undistributed pressure can be destructive, which is especially true for those places where there are floor beams, in which case the edge of the wall crumbles.
To disperse pressure, the Mauerlat is placed on the crest of the wall. It is made of a thick square bar with a side of 150 mm. But when the rafters are fastened to the floor beams, then under the weight of the roof the walls will not collapse, because the Mauerlat will becomeplay the role of an unloading element. In order to protect block or brick walls when they are subjected to high loads, a reinforced concrete belt should be made in their upper part.
Mounting principles
Today, rafters can be attached to floor beams in one of several ways. In this case, it is necessary to exclude the possibility of slipping of the rafters from the support. For this, it is necessary to use joints with spikes and grooves, which are prepared in both elements.
An alternative solution is metal fasteners. The fastening of the rafters to the floor beams can be carried out using bolts. In this case, the kit consists of a nut, bolt and washer. At the end of the beam, which protrudes from the back, it is necessary to form a triangular cutout. Its hypotenuse should be located at an angle that matches the slope of the rafters. The lower part of the rafter leg is sawn at the same angle.
When the rafter is installed on the beam, it must be strengthened with nails, and then a through hole must be drilled, which will be perpendicular to the rafter leg. Holes are needed for the bolts, they need to be located from below and passed through the cutout that is in the beam.
The washer is put on the bolt, and with the help of the nut it will be possible to fix the knot. Wooden elements weaken over time if the rafters are fastened to the floor beams of a pitched roof using through holes. For this reason, the mostspike, stop and tooth connections are common.
When looking at mounting options, you should note that the configuration will depend on the angle of the ramps. If the ramp is steep, it will experience a reduced snow load, in which case it is sufficient to use a single tooth mount. Double is used when installing the roof, if the angle of inclination is less than 35 °. This type of fastening allows you to increase the area of \u200b\u200bsupport and ensure high knot strength.
Fastening the rafters to the floor beams, the photo of which you will find in the article, can be carried out by cutting. In this case, we are talking about an ordinary tooth, which is made with a tenon cut, which eliminates lateral movement under load. Under the spike, it is necessary to provide a nest, which is located in the beam. In order not to weaken it, the depth of the nest must be calculated taking into account the thickness of the beam, the former will be from 1/3 to 1/4 of the latter.
Departing from the edge of the floor beam 25 cm, it is necessary to make a cutout to prevent chips. The double tooth is complemented by a pair of spikes, a key connection and an emphasis with a spike. The latter may also be without a spike. Both teeth should have the same incision depth, but you can use a different incision depth if necessary. In this case, we are talking about the case when the first tooth is complemented by a spike. Cutting is carried out by a third of the thickness of the support beam. The second tooth is cut in half.
Additional mounting recommendations
Considering attachment methodsrafters to the floor beams, you must take into account that the grooves cannot hold the rafter legs, which are loaded. In addition to the cut, with the help of metal fasteners, it is necessary to fix the connecting node. If we are talking about fixed joints, then the nails must be driven in at an angle. You can use metal pads or connections in the form of clamps. The fastening of rafters to the floor beams of a gable roof with any technology is supplemented with forged wire, which strengthens the connection and is fixed on the anchor. The latter is wall-mounted.
How to ensure a reliable connection
Rafters with a beam will be securely connected if you use quality fasteners. These should be steel elements with anti-corrosion treatment, which are based on durable material. Cuts and cuts should be done as carefully as possible, while gaskets and liners should not be used, which reduce the strength of the assembly, and eventually deform or fly out. It is important to use templates if there is a need to make a cut or wash down. In the process, truss fasteners are used.
Fixing the rafters to the frame
The system of rafters on the frame is installed according to a certain algorithm. This is due to many factors. Firstly, the structure of wood has its own geometric dimensions, which can change during shrinkage. Secondly, fastening can be affectedair humidity. Be sure to check the last crown for horizontality so that the rafters lie correctly and the load transfer to the structure is uniform.
Places for installing rafters must be marked. If the pediments are made of timber and logs or beams, then a ridge beam will rest on them, in this case the technology for attaching the rafters will differ from rigid fixation, where metal corners or cuts are used.
How to avoid mistakes
Gables in the process of shrinkage will change their original dimensions, decreasing in height by 15 cm. Therefore, the rigid fastening of the rafters to the floor beams with a nail will cause deformation of the rafter legs. As a result, cracks form throughout the roof. In order to eliminate such problems, sliding fasteners are used when installing rafters.
Need for overlap when bolting
If you still have not decided which technology to install the rafters, you should take into account that the connection of the legs in the ridge part is made movable, because the angle should change when the gables shrink. The rafter legs are fixed with an overlap, and bolting is required for this.
An alternative solution is the use of mounting metal plates, it is important to provide clearance and arrange the elements butt. The rafter legs are fixed from below with a groove that is made in the upper crown. The rafter should be installed with an overhang, and itsthe value will be determined during the design process. If necessary, the fastening of the attic rafters to the floor beams is carried out in such a way that the element is located with an edge on a log, a groove is not required. An option can be used when the horizontal beam of the floor acts as the attachment point.
For reference
In the process of building a roof, you need to pay attention to all the little things. From this, as well as from the quality of the materials used, the durability and strength of the structure will depend. For example, when fixing rafters to floor beams, which is quite rare, it is necessary to follow the technology. This approach is also relevant for wooden, block and brick houses. Including those built from foam blocks.
Conclusion
In each of these cases, you need to observe your installation features. For example, if the rafters are attached to the floor beams in the case of a gable roof, then the structure is quite strong. In this case, the point load increases, but this does not have any effect on the strength of the walls. Everything is explained by one circumstance: long beams are used during construction, and the floor beam exerts pressure on them, like rafters. As a result, it is possible to achieve an even distribution of the load over the entire wall.
