Metal roofing being the most durable despite criticism

When planning a new roof or its renovation, we often come across many questions including the choice of roofing. Which one to choose – concrete, clay, metal, or any other? This time, let us talk a bit more about the installation and metal roofing.

A pore next to a pore but it still does not leak

Take this example, for instance: a thatched roof is limited in time; however, it can serve as a good roofing system for many years if both fastening and the material are proper. Concrete and clay roofing does have its advantages, whereas metal roofing somehow seems to be in the firing line most often. On the one hand, there are exaggerations about its strengths, and on the other, exaggerations in its supposed weaknesses. In fact, metal roofing is one of the most durable roofing systems; it is resistant to hail and other precipitation, as well as wind. However, it cannot be denied that in the event of major wind storms, especially on public buildings, surprising as it may sound, metal roofing is the one that is most often damaged.

Although, not all. And let us provide an answer to one more question, i.e. the problem of condensation under the roofing.

There is no need to talk about the roof insulation, as it needs to be well calculated and optimal. However, it is not wise to save money on thermal protection of the building. In all kinds of roofing systems, it is essential to think about how to extend the phase shift of the heat transfer by installing thermal insulation of an appropriate thickness in order to prevent overheating in attic rooms.

Condensation

First of all, let us consider the problem of condensation that is frequently set out in connection to metal roofing. Condensation occurs in all roofing systems, regardless of material; however, it may be a bit less visible in smaller tile formats or the more absorbent ones. It is because there are more slots between the tiles, enabling the condensation to dry quicker. Nevertheless, the ventilation space is compulsory under all roofing, and it has to be properly installed and provide sufficient air intake to allow the condensation to dry. There is practically no difference between classic and metal roofing systems if the installation is of high quality. The roof must have an open ventilation space, vapour permeable foil, thermal insulation and a vapour barrier.

There is an interesting example. Last year, one roofer covered a multi-apartment building with a metal roof. The residents were very satisfied, but a few weeks later the roof started to leak even though there was no rain. At first glance, the main problem was the roof, but the situation in the attic showed something completely different. The roofer forgot to install the ventilation shaft in leading from the kitchen to the outside, therefore all the moisture ended up on the attic under the roof. Luckily, it at least leaked on the underside of the roof to the outside. The problem was solved immediately by installing an air shaft, connecting the ventilation shaft to the open air outside.

Hail resistance

The advantages of metal roofing are their high resistance to precipitation and their durability. One of the oldest metal roofing systems was installed at Dvor industrial building more than 100 years ago and it does not even look its age. Due to its worth, it was stacked up in the process of building reconstruction and every piece was numbered. This roofing system even now serves as one of the exhibits in Educational and Production centre of Ironworks in Dvor, and some tiles were used again to cover a part of the roof.

What about the wind?

Interestingly, on certain occasions and in the event of very strong winds, some metal roofs are lifted, especially those of larger formats. And it is reasonable to ask ourselves why. This is most likely to happen on different public buildings where the roof may have been restored and the selection process was based on the lowest possible price. This is also the answer to why roofs sometimes fly. The reason is poor installation, failure to use many fasteners or even using the wrong ones, and often a roof design that is architecturally incorrect. Not only does the wind cause a pressure on the roof, but also acts as a suction force, both on steep as well as gently sloping roofs. The stronger the wind, the higher the difference in pressure, causing buoyant forces to act on the roof perpendicularly. This lifting wind force is the main reason for damage to roofs with vertical fastening, where the fastener is easily pulled out.

This is, just as an example, also one of the reasons why it is necessary to use scrails that at least partly prevent the loosening of nails when the wood starts to get dry. This applies to all roofing systems and roofing elements, both concrete and clay (ridge, edges of the roof, etc.) that are fastened. There is an increasing tendency to use this technique. However, there is another solution possible and it is used with Gerard roofs. The roof tiles are fastened with horizontal fastening elements, i.e. with scrails or nails that are nailed horizontally. In this case, the fastening elements must shear off for the roof to fail, an unlikely event given that there are eight or more fasteners holding down each tile. Furthermore, it is also very important that the roof is "sealed", not entirely, but to prevent the wind force coming under the roofing.

All additional elements

Metal roofing manufacturers were among the first to start producing all additional elements, i.e. those to ensure the air duct, protection, and wind protection systems, therefore even the eave has a part that ensures the wind does not enter the area under the roof. The advantage of these additional elements is significant, therefore the majority of roofers dealing with metal roofing use it. Furthermore, additional original elements are used with other roofing as well.

Which roof to choose then? Good, high-quality, but always bear in mind that each roof is its own system. It is not only the roof that should be of high quality and properly installed and fastened. It should have an open ventilation space, vapour permeable foil, thermal insulation and a vapour barrier, and a layer of two in between to extend the phase shift of heat transfer.

Mr. G
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