Fuktskadad KLT-platta på mark - uttorkningsanalys

Sammanfattning

In order to reduce CO2 emissions in the construction industry, more attention should be paid to alternative material choices in cases where it is possible. The study focuses on foundations for single-family houses in Sweden where the concrete in a slab on ground is replaced by cross-laminated timber. Cross-laminated timber, which is more commonly referred to as CLT, is a material that has recently gained great influence as a sustainable alternative to use as a frame system in buildings. Today, foundations are still largely done with concrete, but the interest in laying foundations with CLT in the form of slab on ground has in recent years become a talked about topic among several actors in order to reduce carbon dioxide emissions in this part of the construction process as well. The purpose of the study is to investigate how a CLT slab as a foundation copes with moisture load in a situation where free water lies on the slab. With the help of the moisture calculation program WUFI Pro, the CLT plate is checked under normal conditions with and without moisture membrane but also when it is exposed to a flood. In the event of flooding, it is checked how the moisture is allowed to spread both with a fully functioning moisture membrane but also in the case where the slab has no membrane. The time it takes to dry out the slab so that the moisture ratio is below a critical level is calculated depending on how long free water has been on the slab. When drying, a comparison is made for how long the drying time will be depending on whether the drying is assisted by a heating fan that raises the temperature and lowers the relative humidity or if the plate is dried under normal conditions. A comparison is also made for the drying time depending on whether the wet floor is allowed to remain or if it is removed after flooding. The study showed that the most beneficial thing was to remove the floor and install a fan heater. After a week of flooding on a slab that did not have a membrane, it took five days for the slab to reach below critical condition in the case where the floor was removed and a fan heater was installed, while it took 20 days if only the floor was removed and drying took place in a normal indoor climate. If instead two cases in a normal indoor climate were compared after a week of flooding, the drying time was 20 days if the floor was removed compared to 150 days if the floor was left on. The calculations are performed in 1D between the indoor climate and the ground, which means that moisture migration only occurs perpendicular to the fiber direction. It does not take into account how the moisture spreads in joints or along the fibers out on the ends of the plate, nor is it taken into account for installations in the plate. The calculations refer to cases with a tight climate shell and assume that the wood is delivered directly from the factory. Keywords: Cross-laminated timber, foundation, moisture, WUFI, single-family house