- When a flat roof is convenient
- Technical or maintenance roof
- Insulation system
- Roof support system
- Coating and waterproofing
- Drains and protective elements
Gable and hip roofs are considered traditional in Russian construction, but this form factor is by no means the only one and is absolutely optional. We will talk about what a flat roof structure can be, and what are its technological features.
When a flat roof is convenient
The idea of equipping a pitched roof suggests a number of advantages, among which the most important is savings by reducing the material consumption of construction. Indeed, a flat roof has a smaller area of slopes and gables: in comparison with a classic gable roof at 35 °, 40% less roofing is consumed, while eliminating the need to protect a junction with a ridge on the convergence line of the slopes. The costs of additional systems are also reduced: the catchment is located on only one side, as a rule, the installation of snow guards and walkways is not required.
There are building projects for which multi-pitched roofs are simply not suitable. For example, due to the large elongation in the plan, with the non-standard shape of the building and the need to arrange a complex multi-pitched roof, or simply due to the small size of the building. In other words, when the rafter system takes on a too complex configuration, and the attic space formed by it is inconvenient and little or simply not provided for by the design of the building thermal protection system.
At the same time, flat roofing shouldn’t be a mere whim. This is a rather complex engineering system with a number of drawbacks, besides, the savings on materials are partly offset by the costs of installing waterproofing, a reinforced supporting system and ensuring the stability of walls and foundations to increased loads, because the dead weight and the amount of snow retained at a flat roof is significantly higher. It is important to emphasize that the correct choice of a flat roof can also be dictated by architectural and practical considerations, for example, if you want to exploit the roof surface or realize natural lighting with under-ceiling loopholes in rooms located against the sunny side..
Technical or maintenance roof
The pitched roof system has two technical implementations. One of them is allowed to use a flat roof surface, that is, the design is carried out taking into account additional walk-through and payloads. In other words, the roof simply turns into another floor, but open. The practice of operating roofs notes the high convenience of forming recreation areas, expanding the economic territory, provides ample opportunities in terms of floristry.
But at the same time, a technical roof, which performs only the function of insulation and protection from precipitation, is considered the most budgetary option and therefore is more widespread. A clear difference from a flat roof is that, as a result, the surface of the coating is strongly inclined, which does not allow moving along it without additional superstructures. In terms of the supporting system and insulation, there are few differences: although additional loads should be provided for the operating roof, they are not very significant compared to the snow.
Thermal protection is required for flat roofs. The difficulties of its device lie in the impossibility of separating two belts of thermal insulation with an air gap. All insulation is laid in one layer and is located mainly in the overlapping cavities. Thus, the project should provide for the complete elimination of cold bridges, which can be achieved by arranging a cross system of beams and trusses.
In some cases, the roof can be insulated with an external belt, for example, when constructing an inversion roof or insulating the under-roof space with sufficient attic dimensions. It should be noted that both described cases are quite exotic, as a rule, the space inside the reinforced supporting system is enough to accommodate a sufficient amount of insulation in it. A separate mention is only the requirement to ensure that the lower layer of bulk insulation is heated to a positive temperature at a height of 100-150 mm from the waterproofing, which is possible only when carrying out a detailed heat engineering calculation.
Inversion roofing device: 1 – floor slab; 2 – slope-forming screed; 3 – waterproofing; 4 – thermal insulation; 5 – geotextile; 6 – drainage; 7 – geotextile; 8 – cement-sand screed; 9 – tiles; 10 – parapet
For a number of flat roofs, a warm attic can be recommended. This solution implies the organization of a sealed roof space heated by exhaust ventilation air. In this option, an external heat protection belt should be placed in the roof plane, or the crate should be knocked out with a vapor barrier with a double-sided ventilation gap, otherwise condensation is likely to form on the back surface of the roofing.
When installing shed roofs, it is allowed to use sandwich panels with all their inherent advantages. The benefit is most pronounced in flat roofs attic, where the back of the panel forms an almost finished ceiling. Composite panels in a metal sheath can also be used in the construction of an exploited roof. However, in both cases, they do not have additional bearing properties and require a support system to withstand increased snow loads..
Roof support system
A rafter or other supporting roofing system is the most critical element; the durability of the entire structure and its trouble-free operation depend on its reliability. No wonder the development of this part is devoted to the lion’s share of recommendations for the construction of a pitched roof. At the same time, several types of roofing can be distinguished, depending on the peculiarities of its binding to other building structures..
A flat roof does not have to be the main and independent shelter from the weather. Quite the opposite: most often, terraces or annexes are covered with a pitched roof, that is, with its upper edge, the roof adjoins the building wall or pediment. In such cases, an intermediate beam fastening system is used, which is flatly fixed with distributed fasteners to the wall and serves as a support for the main floor beams located along the slope line. On the other hand, the beams rest on a Mauerlat, fixed or embedded in the end of the outer wall, and the beams have an overhang that forms a soffit and are protected from shear by an undercut at the abutment to the support bar.
Another version of the device is a completely independent roof, the design of which can be implemented in two ways. The first one implies different heights of walls opposite in the direction of the slope, that is, the pediment at such a roof is deaf and passes into the wall. An alternative is to install the truss structure on a system of trapezoidal trusses, the upper plane of which serves as a slope-forming one, and the lower one is designed for cross-linking and fixing thermal insulation.
The supporting system of a flat operated roof has its own characteristics. First of all, you need to take into account the need to erect a parapet that encloses the roof around the perimeter, that is, the protection of the Mauerlat and the pediments rise to the same height, dullly closing the ends of the roofing cake. In this case, the rafter system is located under the ceiling and can be represented by parallel trusses or beams supporting the insulated floor or walled up inside it. The most remarkable thing in such a device scheme is that the beams and trusses do not have a departure, so there is no way to form a soffit, which should be taken into account in determining the overall architectural appearance.
Coating and waterproofing
For non-exploited roofs, the same requirements for the selection and installation of roofs apply as for all other types of roofs. A wide range of materials can be used, manufacturers of which allow their products to be operated with such a small slope. For minimum slope angles of 3–5 °, most roll materials are suitable, especially weldable roofing recommends itself. Slopes at 5–7 ° can be covered with folded or profiled sheets, from 11 ° – with a soft roof and from 15 ° – with metal tiles. As a rule, there are no steeper slopes for single-pitched roofs..
Due to the lack of the possibility of snow and ice melting, single-pitched roofs are operated in a very intensive mode, and in winter they are almost always in contact with water. On the one hand, this obliges to choose roofing materials with better quality coatings, on the other hand, to pay maximum attention to the waterproofing device. For traditional single-pitched roofs, roofing material and waterproof membranes are excellent for these purposes, for flat operated and inverted roofs – fused waterproofing and banner fabric.
Quite often, the general recommendations of manufacturers for the installation of the waterproofing materials supplied by them are irrelevant when installing single-pitched roofs. Due to the high risk of leakage, it is necessary to increase the width of the overlap, as well as the thickness of the deposited layer or the number of layers of roll waterproofing. Almost all modern materials can be used for waterproofing a flat roof, but only on condition that additional recommendations from the manufacturer were previously received regarding the use of specific products at such small slopes. Otherwise, the choice of the type of waterproofing is a matter of, in fact, trivial savings.
Drains and protective elements
The final stage of the roof design is the calculation of special systems designed to facilitate and increase the safety of maintenance. In this regard, with single-pitched roofs, the situation is quite simple: as already mentioned, their slope is rarely steeper than 20 °, and therefore the installation of snow guards is almost never required. With walkways, the situation is similar, because at such angles, you can move along the roof without special devices.
However, operated flat roofs for the most part require the installation of protective fences, and technical ones – careful, high-quality finishing of wind and cornice overhangs. The drainage system of traditional roofs is located on one side of the roof in the lower part of the slope; inversion, as a rule, are equipped with an internal storm sewer. On the one hand, this reduces the volume of work on the installation of trays, but at the same time it is imperative to ensure the appropriate throughput of the system, because water is collected in this area from a large area. By the way, flat roofs can be used without a drainage system, but the foundation must be equipped with a blind area at least 1/5 of the length of the slope.
To summarize, the false sense of technical complexity caused by pitched and flat roofs is most likely due to their unusualness. Such roof systems are easy to design and install, even for construction enthusiasts, and subsequently protect housing for a long time and reliably. But there are also a number of prerequisites: correct application of technology, correct choice of type and use of high-quality materials with the appropriate purpose.