Roof fasteners

Despite the fact that fasteners are often hidden components of the system, and their cost, as a rule, does not exceed 5% of the total cost of building materials, they ensure the reliability of connections, ease and speed of installation, and as a result, the safety and durability of the roof structure.Unreasonable savings on fasteners, the use of self-tapping screws, screws, dowels, etc., designed for less load or made of low-quality material, makes fasteners the most vulnerable part of the roofing system, which can ultimately jeopardize the integrity of the roof structure.The main requirements for fasteners in connecting nodes are:The required strengthcorrosion resistance;impermeability to precipitation (rain, snow, hail);High level of suitability for installation work.Fasteners in most cases are made of steel. Stainless steel is considered the best material for outdoor applications.However, in Russia, products with a protective zinc coating are more popular, which protects parts from the corrosive effects of the external environment, since their cost is three times less than similar products made of stainless steel.
Zinc protective coating is obtained in two ways: by immersing products in molten zinc (at a temperature of 450-480C) The thickness of the electro-galvanized coating is from 5 to 35 microns.The anticorrosion resistance of zinc coating can be increased by passivating the product in a solution of chromic acid. Moreover, the protective properties of the film (from a chromium and zinc compound) do not even affect scratches. Roofing screws are equipped with special sealing gaskets to ensure the tightness of the attachment point. Leading manufacturers of fasteners use only gaskets made of weather-resistant rubber with increased elasticity, resistant to temperature and chemical influences.Rubber washers of nameless self-tapping screws begin to collapse after two years of operation, which leads to depressurization of the roof structure.Although even a high-quality gasket with unskilled installation can perform its functions poorly. If the self-tapping screw is not screwed in enough, a gap remains between the gasket and the roofing material, into which moisture is sure to penetrate. An overtightened self-tapping screw compresses the gasket too much, turning it into a kind of funnel, and sometimes destroying it, so there is no guarantee that there will not be a leak in this place. Under a correctly screwed-in self-tapping screw, the thickness of the gasket should be the same.The optimal choice of type, size and number of fasteners depends on many factors.First, from the material of the roof.Secondly, from the potential loads to which the fasteners will be subjected during operation. Loads can vary in magnitude, in direction (longitudinal (tearing), transverse (cutting), angular (the sum of the first two). In addition, loads may or may not change over time. For example, wind loads are determined by the geographical location of the building, the wind rose in this area, the height, slope and architecture of the roof.Thirdly, from the design of the connecting nodes and the underlying material. So self-tapping screws for wooden crates usually have a reduced drill, but a large thread pitch. They are much longer than metal screws. Since the tree has a rather loose structure, for reliable fastening it must contain at least 25 mm of the "body" of the self-tapping screw. In the case of a metal substrate, for the correct choice of fasteners, it is necessary to know its thickness (2-5mm, 4-8mm, 8-12mm). Obviously, a certain type of self-tapping screw corresponds to each size.Serious manufacturers produce special catalogs that contain technical specifications for the entire range of fasteners and a list of loads that can act on various types of fasteners. Using this information, designers can make the necessary calculations and select fasteners. But as you know, in construction, many materials are interchangeable with analogues, especially such a “trifle” as fasteners. In an environment where the domestic market is littered with cheap products from Southeast Asian countries, for which it is unlikely that it will be possible to obtain technical specifications or quality assurance, the issue of the reliability of fasteners becomes a problem.Quality products of well-known manufacturers are necessarily certified. Even the labeling of such fasteners contains a lot of useful information; the packaging has a company logo indicating the main characteristics of the product.But even the best fastener can be spoiled by unskilled installation. For example, in the technical specifications of the screws there are recommendations for the optimal number of revolutions and torque of the power tool.Thus, choosing fasteners from well-known manufacturers with certificates, the consumer chooses a durable roofing