Transient and quasi-steady thermal behaviour of a building envelope due to retrofitted cavity wall and ceiling insulation

Accurate understanding of the thermal behaviour of building components is essential for predicting heating or cooling needs and facilitates the implementation of more successful energy saving strategies and retrofits. This paper focuses on a specific measure commonly introduced through the residential energy efficiency retrofit programmes in Ireland–insulation. Traditionally, assessments of the performance of building envelopes have been based on assumed thermal resistances of the materials involved, laboratory tests and computer modelling. The aim of the present work is to investigate the in situ thermal behaviour of a case study building and its components under transient and quasi-steady environmental conditions, comparing data before and after the fixing of cavity wall and ceiling insulation. The paper concludes by proposing that predicted values of heat loss using standardised assumed material properties of the existing structure do not reflect the actual values achieved in situ for this test case. These values greatly overestimated the impact of the retrofitted insulation on heat loss through the ceiling and wall.

► Thermal behaviour of an in situ cavity wall and ceiling with and without insulation.
► 100 mm cavity insulation resulted in a 56% reduction in heat loss through the wall.
► Loft insulation resulted in a 35.5% reduction in heat loss through the ceiling.
► In situ R-values are not reflective of nominal R-values.
► Cavity wall insulation causes the internal layer to act as a heat storage device.