The rafters are fastened to the floor beams during the construction of attic roofs with low weight. The attachment points are obtained as reliable as possible, if you choose the installation option and follow the technology.
Features of the rafter system
When designing the roof structure, it is necessary to choose the appropriate option for the rafter system. Among others, it is worth highlighting the overhang and hanging rafters. Hanging trusses are usually used for lightweight roofs of impressive size. For them, the walls act as a support.
More thorough and complex is a system with layered rafters. In them, the rafters have additional support points. When erecting a roof, the rafter system relies on a Mauerlat, which is a structure on the longitudinal walls or installed around the perimeter of the house. This option of attaching rafters to floor beams is used if the house is built from blocks or bricks.
If a concrete monolithic beam is located at the top of the walls or the walls are made of logs or timber, then the roof rests on a horizontal beam, and not on a Mauerlat. Beams in this case overlap the construction box in the transverse direction. The simplest option for a light attic roof is a roof frame that rests on beams.
In 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. The rafters can be attached to the floor beams without a Mauerlat only if the walls of the building can withstand impressive point loads.
In which cases the rafter system is based on floor beams
If for hanging rafters, floor beams serve as a support, then the system creates high loads on building structures. This approach is relevant for the construction of wooden houses, because a beam 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 floor beams are located, in this case the edge of the wall crumbles.
To disperse the pressure, the Mauerlat is laid on the crest of the wall. It is made of a thick square beam with a side of 150 mm. But when the rafters are attached to the floor beams, then under the weight of the roof the walls will not collapse, because the Mauerlat will play the role of a discharge element. In order to secure block or brick walls when high loads are placed on them, a reinforced concrete belt should be made in their upper part.
Mounting Principles
Today, rafters to floor beams can be attached in one of several ways. In this case, it is necessary to exclude the possibility of rafters sliding off the support. To do this, it is necessary to connect with spikes and grooves, which are prepared in both elements.
An alternative solution is metal fasteners. Fastening 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 notch. Its hypotenuse should be located at an angle that corresponds to the inclination 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 drill a through hole, which will be located perpendicular to the rafter leg. The holes are necessary for the bolts, they need to be placed at the bottom and passed through the cutout, which 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 assembly. Wooden elements are weakened over time, if the rafters are attached to the beams of the shed roof using through holes. For this reason, the most common joints are spike, stop and tooth.
When considering mounting options, you should note that the configuration will depend on the angle of inclination of the ramps. If the ramp is steep, then it will experience a reduced snow load, in this case, it is enough to use a mount with a single tooth. 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 the support and ensure high strength of the site.
The rafters are fastened to the floor beams, the photo of which you will find in the article, can be done by cutting. In this case, we are talking about an ordinary tooth, which is performed with a tenon cut, which eliminates lateral shift under load. Under the spike, it is necessary to provide a socket, 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 first will be from 1/3 to 1/4 of the latter.
Stepping back from the edge of the beam of overlap 25 cm, it is necessary to make a cut to exclude chips. The double tooth is complemented by a pair of spikes, a locking connection and an emphasis with a spike. The latter can also be without a spike. For both teeth, the insertion depth must be the same, but you can use the insertion to different depths if necessary. In this case, we are talking about the case when the first tooth is complemented by a spike. Cutting is carried out at a third of the thickness of the support beam. The second tooth is cut in half.
Additional mounting recommendations
Considering the ways of attaching rafters to floor beams, you should consider that the grooves cannot hold the rafter legs that are under load. In addition to cutting, with the help of metal fasteners, it is necessary to fix the connecting unit. If we are talking about fixed joints, then the nails should be driven in at an angle. You can apply metal plates or joints in the form of clamps. The fastening of rafters to the girders of the gable roof with any technology is complemented by forged wire, which strengthens the connection and is fixed on the anchor. The latter is mounted on the wall.
How to ensure reliable connections
Rafters with a beam will be reliably connected if you use high-quality fasteners. These should be steel elements with anti-corrosion treatment, which are based on durable material. Cutting and cutting should be done as carefully as possible, while it is not necessary to use gaskets and liners that reduce the strength of the node, and eventually become deformed or fly out. It is important to use templates if there is a need to make a cut or washed down. In the process, rafter fasteners are used.
Fastening rafters to the log house
The rafter system on the log house is installed according to a certain algorithm. This is due to many factors. Firstly, the structure of wood has its geometric dimensions, which can change during shrinkage. Secondly, air humidity can affect the mount. It is imperative that the last crown be checked for horizontalness so that the rafters lie correctly, and the load transfer to the structure is uniform.
The installation location of the rafters must be marked. If the pediments are made of beams and logs or beams, then a ridge beam will rest on them, in this case the technology of fastening the rafters will differ from rigid fixation, where metal corners or notches are used.
How to avoid a mistake
The pediments during shrinkage will change their initial dimensions, decreasing by 15 cm in height. Therefore, the rigid fastening of the rafters to the beams with a nail will cause deformation of the rafter legs. As a result, gaps form throughout the roof. In order to eliminate such problems, when installing rafters, sliding fasteners are used.
The need for bolt overlap
If you still have not decided on which technology to install the rafters, it should be borne in mind that the connection of the legs in the ridge part is made mobile, because the angle during shrinkage of the gables should change. Rafter legs are fixed with an overlap, and use for this is necessary bolted connection.
An alternative solution is the use of mounting metal plates, while it is important to provide clearance and position the elements end-to-end. The rafters from below are fixed with a groove that runs in the upper crown. The rafter should be installed with an overhang, and its value will be determined during the design process. If necessary, the attic rafters are attached to the beams in such a way that the element is located edge on the log, a groove is not required. An option may be used when the horizontal mounting beam is the place of attachment.
For reference
In the process of erecting 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 observe 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 own installation features. For example, if the rafters are attached in the case of a gable roof to the floor beams, then the design is quite strong. In this case, the point load increases, but this has no effect on the strength of the walls. Everything is explained by one circumstance: during construction, long bars are used, and the floor beam puts pressure on them, like the rafters. As a result, it is possible to achieve uniform load distribution throughout the wall.