Sheet metal roofs: sequence of work for roofing installation

Sheet metal roofing is an alternative to tile roofing. As always with roofing, the work starts with measuring the roof and ends with acceptance of the work by the roofers. Let us see what awaits us in between these stages. What should be the correct sequence of works when covering a roof with metal sheets?

Regardless of whether you choose a flat or profiled metal roof (tile or trapezoidal sheet), the sequence of works during installation of roofing will be similar.

The installation of sheet metal roofing must start with measuring the roof and calculating the amount of materials needed. Ideally, this should be done by a roofing company hired by us. It is also possible to contract a roofing company to buy roofing sheets and all necessary accessories for the installation of the roofing.

Duration of works is difficult to estimate at the beginning. It depends on the size of the slope, complexity of its shape, type of roofing, but also on the weather, which may cause even a longer break. However, usually the installation of metal roofing does not take more than a week or two weeks, unless the work is divided into several stages.

1. Check the geometry of the roof trusses

Once the roofing material is on site, the team again measures the roof trusses, this time focusing on detecting deviations from verticals, levels and planes. They compare whether the roof slope diagonals are equal, whether the angles between elements are not twisted, and whether the rafter ridges form an even plane.

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Before the roof is covered with metal sheets, any deviations must be corrected by repairing the rafter framing or by adding spacers here and there. In extreme cases, when the rafter framing is in very poor condition (due to old age or carelessness of carpenters), roofers may refuse to continue work until carpenters fix the defects.

Sheet metal roofing – installation of vapour barrier and preparation of grid for profiled sheet metal roofing (roofing tiles, trapezoidal sheet metal) or execution of rigid sheathing for flat sheet metal roofing

Only some metal sheet coverings can be fixed to the load-bearing structure of the roof, i.e. rafter framing. These include the so-called self-supporting metal roofing tiles and special panels made of zinc-titanium sheet.

First, however, the damp insulation made of initial covering foil should be made. It is fixed with staples to the rafters. Once it has been installed, it is possible to make a load-bearing grid for profiled coverings (roofing sheets, troughed sheets) or the aforementioned panels of flat metal sheets. Traditionally, first wooden counter-battens are nailed along the rafter. Then battens are fixed crosswise to them at intervals recommended by the roofing manufacturer. If we bought self-supporting metal roofing sheets or zinc-titanium panels, instead of wooden counter-battens and battens we nail metal supporting profiles perpendicularly to the rafters.

2. Construction of the supporting structure for flat roofing looks a little different. Instead of foil insulation and a grid of wooden battens, rigid sheathing should be nailed to the rafters first.

Rigid sheathing is usually made of boards or large wood-based OSB boards. If such material is not protected against water absorption in the factory, it should be impregnated by painting it with a preparation protecting against fungi and fire. A tight waterproofing should be laid on the rigid sheathing. It is usually made of torch-on membrane. You can also buy a special reinforced initial roofing foil or a separation membrane for flat roofing.

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Before the roofing works are commenced for good, openings should be prepared in the rigid sheathing or between battens for elements which will pass through the slope, e.g. aerial conduits, ventilation chimneys, sewage system vent chimneys. This will no longer be possible afterwards.

3. First flashings

Some flashings have to be installed before the roofing is installed, e.g. the gutter drip strip which drains condensate from under the roofing directly into the gutters. If gutter hooks are not to be screwed to the so-called end board, they must be attached to the rafters or to the rigid sheathing before the gutter drip strip is installed. The same shall apply to gutters.

Before the roof covering is installed, ridges or grilles are fixed to cover the air intake under the roof covering (if it is to be ventilated). So-called valley gutters are also prepared, i.e. flashings at internal joints of the slope necessary in the case of profiled metal sheeting.

4. Sheet metal roofing – laying of the roofing sheets

Immediately after the installation of the supporting structure and waterproofing, the roofing of the roof can begin.

The flat sheets are connected by folding the edges of the strips or sheets – this creates the so-called standing seams and standing seams. The sheeting is also attached to the rigid sheathing by metal holders called clips. Thanks to snaps, the covering does not need to be punched with nails or screws.

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Profiled metal sheets – roofing tiles and trapezoidal sheets – are laid overlapping and screwed to the battens. Special screws with gaskets, so called farmers’ screws, are used for this. After installing the sheets of roofing sheets or trapezoidal sheets, it is still necessary to finish the roof ridges and corners with ridge tiles, i.e. properly profiled flashings made of the same material and of the same colour as the roofing.

5. Installation of additional elements e.g. snow fences, chimney sweeping bricks, ventilation chimneys

To improve the functionality of the roof, it is necessary to equip it with a few small details.

For example, snow stops or snow banks are installed on the slope. These are a kind of barriers to break up snow caps sliding down the slope. They protect the gutters from being torn off. Chimney sweeps are also useful, i.e. small platforms on which you can safely move to make possible repairs.

The roof design often provides for air to escape through the roof through ventilation chimneys. After the roofing has been installed, such ventilation chimneys have to be fixed in suitable places. Finally, the tin roof slopes are equipped with the lightning protection system, i.e. a popular lightning conductor.

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