Gwynne Anthony 2020

ART506 Dissertation 2019. Anthony Gwynne . 16 Figure 1: The SPAB Building Performance Survey 2011 to 2017- summary of findings (www.spab.org.uk/interimreport/2017 ). Building study reference Existing wall construction Thermal upgrading of wall Summary of findings Shrewsbury 350mm thick porous and permeable brick in lime mortar Internally applied 40mm thick wood fibre board and lime plaster finish These finishes are vapour permeable Had the lowest rates of relative and absolute humidity Had the widest saturation margins and lowest moisture content Driving rain penetrated towards centre of wall but dries out rapidly after due to direct and diffuse heat, solar radiation and air exchange through substrate. Has extremes of drying and wetting. Interface between insulation and masonry maintained a stable relative humidity profile below that of the 80% risk profile 1 Long term trend of relative humidity continued to decline Hydroscopic qualities of the wood fibre insulation made a positive to the vapour profile by buffering humidity and flattening out relative humidity responses Overall average relative humidity proceeds downward away from the 80% risk threshold 1 Drewsteignton 580mm thick granite in lime mortar Internally applied 100mm thick polyisocyanurate (PIR) insulation board, with plaster board and skim internal finish. Reduces the U-Value from 1.2 to 0.16W/m 2 K. These finishes are not vapour permeable Average relative humidity was above 90% and well above the threshold for mould growth 1 and is a risk to organic materials embedded within the wall such as joist ends, timber bearers and wall plates etc. Rising trend of humidity within the centre of the wall and moves this part of the wall closer to saturation conditions and can cause deterioration of the building fabric Trend of rising humidity is not solely a response to atmospheric conditions but also a function of the construction that inhibits drying of the wall The insulation itself has a negative impact on the wall’s performance as follows: -less heat passes into the cold side of the wall during winter and saturation margins are lower -air likely to become saturated and remain saturated for longer periods, limiting drying potential