Improving the airtightness of existing plasterboard-lined load-bearing masonry dwellings

Abstract

This paper describes an approach that has been undertaken to improve the airtightness of a number of plasterboard-lined load-bearing masonry dwellings that were constructed in the early 1970s. Such dwellings are likely to be broadly representative of many of the dwellings that will be refurbished in the UK over the next decade or so. The airtightness of the dwellings was improved by undertaking a two-stage programme of general and targeted airtightness work, in parallel with a basic domestic refurbishment programme. The results illustrate that prior to the refurbishment, the dwellings were in a poor state of repair and had an air permeability of between 24 and 26 m3/h per m2 at 50 Pa, which is substantially in excess of the UK mean of 11.5 m3/h per m2 at 50 Pa.1 The condition of the dwellings also suggests that the air permeability of these dwellings is likely to be considerably higher than that which would have been experienced when they were first built. Following the refurbishment programme, it was possible to reduce the air permeability of these dwellings by almost 55%, to a mean of just over 11 m3/h per m2 at 50 Pa. The paper also identifies a number of factors that limited the effectiveness of the airtightness work. These factors included: wear and tear of the plasterboard-lining; detailing and workmanship during the refurbishment programme; and, the partial nature of the refurbishment programme. Had it been possible to address a number of these factors during the refurbishment programme, the authors are reasonably confident that an air permeability of less than 10 m3/h per m2 at 50 Pa could have been achieved in all of the dwellings. Despite the small size of the sample (only 12 dwellings were tested), the results suggest that the airtightness of existing plasterboard-lined load-bearing masonry dwellings can be improved to a level that is comparable to the current UK Building Regulations (Approved Document Part L1) requirement for new dwellings.2 Practical application: Airtightness is crucial to improving the energy performance of buildings. In the UK, existing dwellings tend to be very leaky compared to some of their international counterparts. The use of plasterboard-lining as an internal finish to external and party walls makes a significant contribution to this poor performance, particularly where it is not edge sealed. Air leakage measurements reported here for dwellings built in the 1970s suggest that if this construction is allowed to deteriorate, very high leakage rates may result. Considerations of the impact of choice of construction on future robustness and durability of airtightness of new housing is likely to be an important practicalconsideration, particularly for social housing providers. Separating the air barrier function from the plasterboard lining appears to provide a more reliable and probably more durable solution.3 The paper goes on to describe how injecting expanding polyurethane foam into the cavity between the inner leaf of blockwork and the plasterboard-lining to form continuous ribbons of foam can seal the plasterboard lining and prevent air movement within this cavity. If this approach is undertaken in parallel with a domestic refurbishment programme, the air leakage rate of existing plasterboard-lined masonry cavity dwellings was shown to be reduced to a level comparable with the requirements of the current Part L1 for new dwellings.