Uttorkning av träregelväggar efter översvämning

With the climate change sea levels are rising which changes the boundary conditions for sites along the coast. The County Administrative Board of Skane has decided that new buildings should be built at least 3 meters above sea level. Because of this decision the coastal municipalities have problems with expanding further, and are really keen on finding alternative solutions in order to allow buildings in exposed sites. One possible solution is to accept that floods may happen and to build in a floodproof way in order to minimize the damages from flooding. Flood-proof buildings can mean either watertight constructions or constructions that dry out easily after flooding. This master thesis examines whether a typical Swedish house with a timber-frame can be dried out after flooding without risking mould growth on the load bearing structure. Floods are often devastating - almost all floods in Sweden during the last 110 years have affected economic interests. The County Administrative Board of Skane took the decision of banning new construction below + 3 meters above sea level based on that the sea level is rising and the risk of coastal floods will increase. However, from a historical point of view only 2.6 % of the floods in Sweden during the last 110 years have been coastal floods. The most important factors concerning a flood is the depth and its duration. Damage on property increases with both those factors, therefore it is of outmost importance to limit them if possible. If it is possible a house owner should take measures to prevent the flood from reaching the house, which can be done with temporary or permanent measures. In porous materials water is transported as both vapour and liquid, with moisture transport in the liquid phase being faster than vapour transport. When a material dries it uses both transport mechanics. Therefore the drying period is often longer than the period with absorption. The most important parameter when it comes to drying out is the initial moisture content, and the moisture content is determined by the time in contact with water. Other important factors are the temperature and relative humidity. The drying time after flooding is hard to assess, often a timber-framed building takes a few weeks to dry out properly if the house owner does what is necessary to increase the drying rate. Previous field tests have shown that it takes about 30 days for a timber-framed wall to dry if no special measures are taken. With the help of the hygrothermal modelling tool WUFI it is possible to show that an increase in temperature and decrease in the indoor relative humidity could reduce the drying time to 15 days. Mould is often a problem when a property is water damaged. Mould growth can start when the relative humidity is above 75 % and the temperature is above zero. The mould growth increases with increased humidity and temperature. People living in a building contaminated with mould can experience bad odour and inhaling mould spores can lead to allergies and hyper sensitivity. Laboratory tests verified that water depth and flood duration are the most important factors when trying to assess effect of flooding on timber framed walls. The tests also show that the capillary transport starts instantly, however, the capillary rise is not really high. Moreover, the tests show that the mould problem is real and should not be neglected, as mould growth was detected on some of the specimens after a week. Building flood proof constructions is difficult, instead it is recommended to use flood proof materials that are better suited for drying out. The flood water is often contaminated, in that case the materials in the wall need to be replaced to prevent future problems.