Flat roof slope: flat roof construction

Recommendation points

• Difference between classic and inversion roofing
• Carrying system device
• Slope and waterproofing
• Roof protection

Flat roofs are widely used in modern residential building projects. This is a rather specific type of roof that has a wide range of advantages, but requires strict adherence to the technology of the device of the supporting system and protective coating.

Difference between classic and inversion roofing

There are several types of flat roofs; they differ in the structure of the roofing cake and in some details of the supporting structure. A large number of variations are designed to expand the range of flat roofing applications for various types of buildings. The desire for this is quite natural: a flat roof has the smallest possible enclosing surface area, low material consumption and absolute resistance to hurricane wind.

But such a roof also has a number of disadvantages, the main of which is the problem of draining a large volume of rain and melt water. Roofs, in which precipitation flows down the surface of the coating, allow the organization of the drainage system on only one side. There is a certain limit to the area of ​​the slope, at which the throughput of standard external drainage systems is sufficient. Here, it is also important to take into account the average annual and peak amounts of residues, so that in different regions the limit of the flat roof area may differ significantly..

An inverted roof is notable for the fact that in its pie, the thermal protection circuit is located above the supporting roof system. This is necessary for a simpler arrangement of a hidden drainage system, which is operated at positive temperatures in order to prevent water freezing in the drainage channels. To protect the insulation and facilitate drainage, the top covering of the roof is a hygroscopic material that is resistant to mechanical stress, therefore inversion roofs are often equipped as operated.

Carrying system device

In a classic flat roof, the supporting system is represented by beams or trusses hidden in the thickness of the thermal protection belt. As a rule, mineral wool is used as a heater. It is believed that in a well-insulated house, the thickness of the mineral insulation in the roofing cake should be at least 300 mm, that is, the elements of the supporting system will have a sufficiently large section. This allows the free use of trusses and elongated cross-section beams, the strength of which is enough to cover spans of 6 meters or even more..

When using beams, the slope is formed by the elevation of one wall relative to the other, in the upper part of the beams are attached with anchor pins to the wall body or directly to the Mauerlat. The trusses can be used with the same height of the outer walls, the slope is formed by the upper inclined belt. On the upper plane, the load-bearing elements of the roof are fastened with a crate, which serves as both a plane for a waterproofing device and an array for fixing the roofing.

The main problem of a classic flat roof is that its ends are poorly protected from the external environment, and the surface must be located at a sufficiently large slope to be able to use such popular materials as profiled sheets or tiles. With small slopes of a flat roof, the use of roll deposited coatings is required, which is more difficult to install and more expensive in terms of material costs.

Inversion roofs in this regard are more universal: they allow water to be diverted both along the surface and by a system of hidden gutters. The spreading of such a roof is carried out from the center to the edges, where the drainage funnels are located. The supporting structure of an inversion roof is usually a concrete slab. If the building has internal load-bearing structures that reduce the maximum flight length to 6 meters, the best way to overlap is to fill it with a fixed formwork from profiled sheet. For longer spans, it is possible to recommend floors made of hipped roof slabs PKZH and monolithic on supporting beams.

Slope and waterproofing

According to the well-established classification, roofs with a slope of up to 7 ° are considered flat and suitable for walking, up to 15 ° – low-slope. Nevertheless, for the most part, both of these types of roofs are called flat solely for ease of perception. For flat roofs on beams or trusses, a slope of 15 ° (27 cm / m) is recommended when using sheet materials and from 7 ° (12 cm / m) when covering with roll-deposited materials with at least three layers. Shed roofs have a uniform slope, there are no difficulties with its formation, it is only important to bring the under-roof lathing into a single plane.

Inverted roofs are well suited for irregularly shaped buildings where multiple drainage areas need to be formed. In this case, the roof plan is divided into rectangles, on which parallel axes and diagonals are marked. The drawing of these lines clearly makes it clear which configuration of the slopes will be optimal, according to this scheme, it is necessary to form several planes, with a slope of 1.5-2 °. In addition to the sloping of individual sections, it is necessary to ensure a global roof slope of 3 ° so that water can flow freely along the collection gutters.

The most convenient way to form a slope is concrete preparation without reinforcement. At the same time, the mixture should have a thicker consistency than for the production of monolithic works. The slope-forming layer does not have high strength requirements, therefore, low-grade concrete can be used. Alignment is carried out with a long rod, on which a bubble level with inclined flasks is fixed. Previously, it is necessary to set several reference point beacons on the surface, the alignment of which is performed with a water level or a laser level.

Roofs with external waterproofing, as a rule, are not insulated, the water-repellent layer is applied immediately over the slope-forming screed after priming, applying a primer or coating with molten bitumen. The top layer must be covered with a protective pebble powder. When constructing an inverted roof, PVC membranes on a woven basis are usually used as waterproofing, laid with soldered joints. The insulator is reliably protected from damage and weathering, therefore the only requirement for waterproofing is tightness.

On top of the waterproofing layer, plates of extruded polystyrene foam are laid in 2 or 3 layers with an offset of the joints, fastening them together with a special glue. Before the start of work on the installation of thermal insulation on the roof, a drainage system should already be installed, represented by receiving funnels with an upper drainage cap and a drainage apron located at the level of the main waterproofing.

Roof protection

Roofs with external waterproofing are not protected as such. The service life of the coating is 5-7 years, depending on the intensity of the operational loads, after this period, another layer of coating is simply melted onto the roof.

With inverted roofs, things are more complicated. In order to distribute the throughput load on the insulation, a ballast layer is arranged on the roof. As a rule, porous materials such as expanded clay or sifted blast-furnace slag are used to form it. The thickness of the embankment ranges from 8 to 15 cm, depending on the height of the drainage hoods. The fill must be separated by a geogrid or a special membrane for an inverted roof to facilitate water drainage. Roof protection does not have to be performed with bulk materials, instead of them, a paving slab covering laid on special plastic supports or a loose substrate with a lawn can be used.

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