Moisture-related problems in roof structures with cold attics and retrofitted insulation : A case study on historic buildings and sustainable solutions

Old buildings with unheated, naturally ventilated experiences moisture-related problems to a greater extent, especially those with cultural historical value that do not meet modern moisture safety standards. These buildings require solutions that preserve architectural features, including roof construction. This thesis proposes optimized roof and attic floor constructions for such buildings, focusing on case study of an old Mission Church Kungsgatan 16 in Uppsala, Sweden, conducted in collaboration with MIAB Förvaltning. The study identifies two alternatives for the roof, evaluated for: moisture control using WUFI simulations and long-term sustainability, environmental and economic via lifecycle analyses A1 raw material supply to A5 construction-installation process, costs in “One click LCA”, while respecting the building’s cultural value. Alternative 1 (preserve) prioritizes retaining existing materials. Alternative 2 (new materials) aim to replicate the current exterior roof. WUFI results show that up to 30 % of the simulation period mold can develop in wood in the external roof structure without roofing felt compared to the corresponding number for a roof with roofing felt is 14 %. Alternative 1 (preserve) has a mean value of relative humidity (RH) of 55 % in wood fiber insulation while corresponding number for Alternative 2 (new materials) is 47 % (mineral wool). Neither exceeds the critical 75 % RH threshold after the first month, indicating low mold risk. From a sustainability perspective, Alternative 1 (preserve) has an environment impact as global warming potential (GWP) of 558 kg CO2e and a cost of living 212 140 SEK compared to Alternative 2 (new materials) 6 424 kg CO2e and 331 041 SEK. Conclusion: Alternative 1 (preserve) is the most sustainable option from both the environmental and economic perspective. Alternative 2 (new materials) prioritizes long-term moisture safety.