Thermal performance evaluation of double-skin façade in mid-rise wooden building based on field measurement

The thermal performance of a double-skin façade in Japan’s first mid-rise purely wooden fire- resistant building was evaluated through a year-long field survey. In October, the solar heat gain coefficient for the entire window was measured at 0.46 with the blinds open and 0.11 when the blinds were closed. The design featured a wooden frame structure with a large volume and an offset inner skin layer, which helped shade the inner glazing from May to August. The wooden columns and beams exhibited high thermal performance even without thermal insulation, with a thermal transmittance of 0.22 W/(m²·K), accounting for the effects of the double-skin layer. In contrast, the single-skin façade on the 8th floor, made of Low-E double glazing, had a thermal transmittance of 1.85 W/(m²·K). The overall thermal transmittance for the whole window of the double-skin façade on the 4th floor was recorded at 1.66 W/(m²·K).