Introduction

The method described in BS EN ISO 6946 (also known as the Combined Method in CIBSE Guide A, Section A3, 1999 edition) is used to calculate the U-value of many types of building elements with repeating thermal bridges such as timber joists, structural and other framing, and mortar bedding.

However, when applied to double-skin metal-cladding systems, there are some constructions with significant metal connections between the inner liner and outer sheet where using the Combined Method leads to a significant underestimate of the heat losses.