The impact of workmanship on the thermal performance of cavity walls with rigid insulation boards: where are we today?

Abstract

Even small air paths around the insulation layer in cavity walls may result in a significant reduction of its thermal resistance. This topic of air flow patterns bypassing the insulation layer has been studied in detail from the ‘80s and ‘90s on and let to clear recommendations for building practice [1]. However, the question remains to which extend the proposed research results of that time are adopted in today’s building practice and if so, to which extent they are still valid for current building techniques. The overall aim of the present article is to gain insights into the current installation quality of the insulation layer in cavity walls in Belgium. Moreover, the present article targets to quantify at the same time the impact of workmanship inaccuracies on the thermal performance of these building elements.In a first step the current building practice is mapped in relation to the installation quality of rigid insulation panels in cavity walls in Belgium. A high number of building construction sites has been visited and the installation methods and accuracy are documented. The outcome of this work provides an overview of the configuration of typical air leakage paths in and around the rigid insulation boards in cavity walls for today’s building practice.In the second step of the research, the air flow resistances of the observed air flow paths (e.g. air gap between inner leaf and insulation board, tongue and groove connection of the insulation boards,…) have been measured in laboratory conditions. The characterization of these air flow resistances allows modelling the thermal behaviour of these elements in a following step. Numerical simulations, taking both heat and air transport into account, have been conducted to assess the performance of today’s levels of workmanship. Based on this numerical parameter study, recommendations are proposed to obtain optimal thermal performance in cavity walls.