Fastening rafters - how to properly fasten rafters to the
The rafter system is the frame of the house roof, which bears on itself and evenly distributes the weight of the roofing pie, sometimes reaching up to 500 kg / m2. The reliability of this peculiar skeleton 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 fix the rafters, you can significantly increase the carrying capacity of the frame, making it more durable and reliable. Installation errors, on the contrary, lead to noticeable loss of strength and roof deformations. In this article we will talk about the main types and methods of fastening, with which you can properly install the rafters with your own hands.
The main elements of the truss frame
The rafter frame of a house roof is a system of interconnected supporting elements made of wood or metal, which give the structure its shape, slope, and evenly distribute its weight between the supporting walls. Its main component is the truss legs, which are the beams installed at an angle, which are connected in pairs along the slope, forming a ridge at the top of their joint. There are two main types of rafters:
- Outcast. The suspended elements are called supporting elements, which in the roof structure have two points of support - the ridge girder and the power plate. A truss system of this type is used in structures that have one or more load-bearing walls inside, on which rafters can be “slit”. Such mounting rafters allows you to unload them through the use of additional vertical supports.
- Hanging. Elements that have only one point of support, located where the rafters are attached to the wall or the power plate, are called hanging. Hanging rafter system is experiencing a load not only on the bend, but also on the expansion, so it is amplified by horizontal compensating elements (bolts, puffs, fights).
Note! In most of the most popular roof systems, the rafters are fastened to the power plate. Mauerlat is a massive timber or beam with a section of 150x150 mm or 200x200 mm, laid along the supporting walls of the structure, on which the rafter legs will later be supported. It softens the pressure on the walls of the house, and evenly distributes the weight of the roofing pie. Attach the mauerlat to the upper belt 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, with the result that the roof structure acquires a stable shape, rigidity and high load-carrying capacity. Each connecting node between its parts is a vulnerable point that can easily be deformed under load, so all fastenings must be carried out strictly according to technology. Experienced craftsmen identify the types of compounds in the roof structure:
- Fastening rafters to the ridge bar. This connecting node is typical only for slanting truss systems in which the upper part of the truss foot rests on a ridge girder mounted on vertical racks. Fastening rafters to it can be done with metal lining, nails or sliding fasteners, sliders.
- Fastening rafters to the mauerlat. The most important fixing unit of the truss frame is considered to be the junction of the power beam with the truss legs. To fix the rafters on it using nails, metal corners or wooden bars.
- Connection rafter between themselves. To lengthen the trusses, if the length of the slope exceeds the standard length of lumber, they are collected from several elements interconnected with nails, glue or metal lining.
- Connection of rafter legs with auxiliary basic elements. In the construction of the rafter frame, the rafters can be connected with a puff, a bolt or struts to increase rigidity, strength and carrying capacity.
Consider that any zapily performed to attach rafters to beams, mauerlat or other structural elements of the frame lead to a decrease in their strength, therefore, experienced craftsmen recommend connecting them with the help of corners and overlays.
Fixation methods
Solving the question of how to fix the rafters to the mauerlat or ridge girder, it is necessary to choose the right fitting hardware. The modern construction market has a huge assortment of fasteners of various designs and sizes. The main criteria for the choice of fasteners are the material used for the manufacture of rafters, their cross section, as well as the type of load to which they are subjected. There are the following methods of mounting rafters:
- With metal corners. Metal corners with holes for screws or nails are the most reliable and durable option for rigid attachment of rafters to the mauerlat, walls or ridge girder. They allow many times to increase the stiffness and load bearing capacity of the truss frame structure.
- With the help of metal plates. To connect the truss frame elements, perforated steel plates are also used, which allow them to be fixed without making gash in the mauerlate or rafters, thereby preserving their high strength properties.
- With the help of "chocks". Small square squares are called chocks, which are installed between the rafters and the ridge girder or mauerlat as raskori, increasing the rigidity of the structure.
- With sliding fasteners. Another option for fixing rafters with a ridge girder or a mauerlat is to use mobile fasteners, which in everyday life are called skids or sliders. Due to their mobility, it is possible to compensate for the change in the size of elements that occurs during the shrinkage process.
Experienced craftsmen believe that the most reliable way to fix rafters is to use metal corners, which firmly connect wooden elements to each other, rigidly fixing the angle between them. The corner, which overlaps the junction between the rafter and the ridge bar or Mauerlat, serves as a kind of stretch between them.
Mounts
Wood is a natural material, which in the process of leveling moisture and drying gives a significant shrinkage, due to which the linear dimensions of the structure change. That is why experienced craftsmen recommend building a roof for log and log houses, a year after construction, when the shrinking process moves from the active to the passive phase. If you fix the wooden elements of the frame tightly, then after drying the roof of the house can be deformed. Therefore, to connect the rafters use the following types of fasteners:
- Hard. Hard fasteners are called those types of fastener hardware that are not able to compensate for changes in the size of the wood during the drying process. They provide a strong, reliable fixation, however, they can cause deformation of the frame, leading to a change in the geometry of the roof, leaks or even collapse of the structure. This type of fasteners include metal corners, metal plates and wooden "chocks".
- Movable. Movable fasteners are called fixation methods, which, due to parts sliding along its axis, can compensate for the change in the size of the truss frame in the process of shrinkage of the structure. The frame, fixed with the help of sliders or sleds, “breathes” along with the house, adjusting to its dimensions, without deformations. With the help of such mounts, you can build roofs for wooden houses that have not undergone the process of shrinkage.
Interestingly, there are several variants of combinations of mobile and fixed connecting nodes. The most common are truss systems with one rigid and two sliding fasteners, which provide sufficient mobility with high strength and rigidity of the structure.
Types of fasteners
Among experienced roofers, disputes do not subside, the more efficient it is to mount rafters to floor beams and mauerlat. However, in most cases the snag is that it is more practical to use nails or screws in these conditions. Both of these fasteners have their own advantages and disadvantages:
- Nails are good because they only need a hammer, which is in every household. However, some masters complain that it’s too long to manually hammer them. It is worth recalling that for fixing the rafters special jagged nails are used, which securely adhere to the wood.
- Galvanized self-tapping screws, which are not afraid of corrosion, are used to assemble the rafter frame. Due to the thread they are firmly screwed into the thickness of the wood, securely fixing the elements among themselves. Tighten them quickly and conveniently with a portable screwdriver. The disadvantage of this type of fasteners is that when removing, to remove screws from wood is long and dreary.
Most experienced roofers agree that it is better to use galvanized pierced nails, which are 5–3 mm longer than the thickness of sawn timber, to fix rafter legs. Correctly chosen fasteners - a guarantee of high-quality and long-term fixing of the roof frame, which will not be afraid of any mechanical impact or wind load.
