When developing new designs, as well as when evaluating and optimizing existing technical solutions, it is always necessary to imagine an ideal that should be guided by. Let’s try to formulate what the ideal roof of a modern house is..
Possible scheme of wooden structures for insulated roof sections
Premises under the roof can be used as attics, billiard rooms, sports complex or for placing technical equipment: air conditioning, ventilation, communication facilities, television broadcasting, etc. They should be comfortable, temperature and humidity conditions should not differ from the regime in the house. It follows that the “roofing pie” is an analogue of the wall of a house, but at the same time, the structure must take over and divert water from the house during rain, snow load in winter, withstand the pressure of the wind.
The main problems naturally arise in winter. In a well-heated house at 25 ° C and 30% humidity, each cubic meter of air contains 7 g of water vapor, while outdoors at -25 ° C and 100% humidity no more than 0.76 g / m3. The ratio of partial pressures of water vapor house / street is more than 9. Naturally, water vapor will tend to go out through any gap and leak, therefore a vapor barrier should be provided in the “roofing pie”. In case of insufficient vapor barrier, the insulation lying on top is saturated with condensed moisture and loses its properties, further steam release leads to wetting of load-bearing structures, their corrosion, the formation of condensate flows, and icicles fouling the roof. It should be taken into account that the previously used conventional polyethylene vapor barrier film ages faster than the main structures, and therefore it is necessary to use specially designed durable vapor barriers.
Warm air, lighter than cold air, as a result of natural convection, it accumulates under the roof. The problem of thermal insulation for the roof (saving energy!) Is more acute than for the walls. The standard thickness of Roomfate-type solid insulation ranges from 84 mm at the first stage of the introduction of standards to 112 mm at the second. If you use a minelite on a synthetic binder, the corresponding thicknesses are 141 mm and 188 mm. However, the whole point is that the insulation cannot be laid in a continuous layer, it is penetrated by various structural elements, and therefore the entire structure as a whole must be subjected to thermal calculation. Errors in insulation will cost dearly to the owner of the house. They will manifest themselves in the outflow of heat through the roof (extra energy costs), melting of snow on the roof, accumulation of moisture in the insulation and building structures, the formation of ice and icicles.
It is impossible to completely exclude the penetration of moisture through the roofing (both due to air vents from the outside, and due to a defect in insulation and vapor barrier from the inside), no matter how carefully the work is done. To prevent further penetration of moisture into the roofing structures and insulation, a layer of additional vapor-permeable waterproofing is arranged from a special micro-perforated film (fabric). Trapped moisture and released water vapor are removed through a permanent ventilation system, consisting of eaves and ridge vents, as well as weather vane.
The top, most critical roofing layer will be close to ideal if it is made of metal with folded edges. Currently, various types of corrugated metals and metal tiles are spreading. The desire to transfer the main burden of the roofing work to the industrial workshop is understandable. Moreover, it is increasingly rare to find master roofers who are at the same time master tinsmiths who know how to make the necessary folds with high quality. The sheets are overlapped both horizontally and vertically. Regardless of any seals and sealants, these joints cannot be considered satisfactory in terms of their waterproofness. Such connections are unsuitable for critical roofs. On the other hand, a well-punched fold, for example, in a tin bucket or can, without any sealants and seals, lasts almost forever. However, metals have a significant drawback: they are subject to corrosion to one degree or another. If you do not consider precious and semiprecious metals, due to their prohibitive high cost, the most passive, corrosive with the formation of stable oxide films, is copper. In the natural process of oxidation in air, within six months, a noble, persistent dark brown oxide appears on the copper roof, which after years will be covered with a barely noticeable greenish patina, which will give the house the appearance of a modern castle. Copper roof – for centuries.
A cheaper option is to use a specially developed titanium-zinc alloy, factory-painted galvanized steel sheet and, finally, conventional galvanizing. At the same time, both the quality of the roofing and its appearance are progressively reduced. So, the ideal roof of a modern house, in our opinion, is: