Brandbelastning i träbyggnader : Jämförande beräkning och kartläggning om hur branschen hanterar permanet brandbelastning

Sammanfattning: Wood is a renewable material, it is strong in relation to its weight, climate smart but also combustible. Owing to its many advantages and the easy access in Sweden, wood is motivated as a topical building material. However, the aspects related to the combustible nature need to be considered in the design of buildings with a wooden frame. Whether and in such cases how to take into account the increased permanent fire load is a problem of which there are shared opinions. Today's regulatory framework is unclear in some aspects in its formulation and thus leaves room for interpretation. The purpose of this work is to investigate the reasonableness of tabulated data for permanent fire load and the sharp boundary between a BR1 building and a BR0 building but also by surveying how the industry handles the issue. In order to assess the reasonableness for the tabulated data, the method has been calculations with two different methods; one that follows BBR's guidelines (method 1) and another where calculations of the charring depth (method 2) have been performed, as well as a survey and a literature study. The result from the calculations in method 1 shows that in order for the level of the total fire load not to exceed the standard value for a residence of 800 MJ/m2, a low coefficient is required, and thus in principle all wood is assumed to be protected. According to the calculations in method two, it is possible to read out how the permanent fire load is affected by different protective linings and carbonation rates. The survey shows that the most common way to dimension fire protection is through simplified sizing, which entails that one does not have to consider whether the permanent fire load increases due to a combustible frame. There are divided opinions about whether Boverket's rules are enough to achieve adequate protection and how to handle it. The literature study shows that for the timber frame to be counted as fully protected it needs to be three layers of fire gypsum board in the ceiling and that two layers on the walls. Several conclusions can be drawn; the calculations indicate that a permanent fire load of 200 MJ/m2 (2013:11) is unreasonable in a wooden frame building also that if the permanent fire load is considered it becomes costly both economically and in terms of space. Even that Boverket's rules need to be clarified and adapted further against tall wood buildings and that fire projectors work differently and the experience of working with tall wood buildings differs greatly.