Anyone who buys a turnkey house usually gets a house from the prefabricated house manufacturer that meets the minimum values prescribed by law. For example, the masonry consists of a 17.50-centimeter-thick sand-lime brick wall with a facing layer of polystyrene up to 20 centimeters wide. The purpose of this facing layer is to ensure that the legally required energy values are achieved in the building and serves as a thermal insulation system.
Even though these constructions are standard nowadays, the Association of Private Builders (VPB) points out that this type of composite thermal insulation system also has disadvantages. Because if there is a fire, polystyrene does not burst into flames, but swells over a large area, melts and subsequently drips from the facade on a large scale. On the one hand, this makes it difficult for the fire department to enter the building, and on the other hand, it makes it difficult for the occupants to leave. In addition, the chemical compounds released from the burning material are toxic.
According to the VPB, the fire hazard could be avoided by installing strips of mineral wool about 10 centimeters wide. These would have to be installed in the thermal insulation above the doors and windows. The mineral wool would prevent the fire from penetrating the polystyrene shell. However, these special parts are not required by fire safety regulations, so they are rarely offered by prefabricated home manufacturers. Builders who insist on the special parts must incur additional costs and include the special request in the contract early on. It is important that builders ensure that the prefabricated house manufacturer provides sufficient smoke detectors at the time of purchase and implements a second escape route.
Source: VPB
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