Life-cycle assessment of timber frame constructions – The case of rooftop extensions

Abstract

Due to the growing population, the revived trend of living in urban areas and the scarcity of building plots, the idea of vertically extending existing residential buildings is gaining popularity in Belgium. Timber frame constructions are appropriate due to their light weight and lack of point loads. This article aims to assess (1) the potential environmental impact reduction of light-weight timber frame constructions for rooftop extensions by changing composition and dimensions and (2) the effect of biogenic carbon. Timber frame walls and roofs are analyzed based on the life-cycle assessment method. Starting from the current building practice in Flanders, various parameters are assessed. The effect of using I-joists instead of solid studs, of adjusting the center-to-center distance between the studs and of changing materials for different layers is analyzed. The results showed a limited environmental impact reduction of using I-joist instead of solid studs and of adjusting the center-to-center distance. Changing the composition of the walls and roofs in terms of materials can lead to a total life-cycle environmental reduction of 22% and 14%, respectively. If biogenic carbon accounting is integrated in the assessment method, based on the ILCD method, the total life-cycle environmental impact is reduced by up to 35% and can lead to significant differences in the preferred choice of timber frame composition.