Dry-lining versus a hemp and lime insulating render - University of ...

Where U errQ , U errTns and U errTout are the U‐values calculated when applying all errors dueto heat flux, internal surface temperature and external temperature, respectively and U isthe original U-value3.4 WUFI modelThe interstitial moisture control modelling investigation was developed in the moistureand heat transfer programme WUFI, from Fraunhofer Insitut. The full development ofthe models is covered previously (Flower, 2011). Two models were based on the twowall sections (Fig 1) and extended simulations performed. The first 10 months ofrecorded data from the cottage provided verification of the models ability toqualitatively represent the patterns of RH and temperature fluctuations (Fig 2).Figure 2: Simulated Data (red) versus real data (blue) in the 36mm mineral wool showing how thegeneral trends are well captured by the model4 Findings and discussionFigure 3 shows that the temperature gradient across the DL wall is steepest over theinsulation whereas the hemp appears to acting as if homogenous. On the warmest daythe external and internal temperature are both higher than the inside the centre of thewall by 5-6 o C and thus heat will be being drawn into the wall from the inside andoutside surfaces whereas steady state would only predict a minor flow from outside toinside.From figure 4 it is evident that in both test walls, condensing moisture has beenoccurring constantly in both warm and cold conditions. This should be expected in theHemp/Lime wall as the materials are still drying. However the construction of the DLwas dry and despite the Vapour Barrier the RH behind the DL is constantly ~100% andhas been so for the entire period of data collection suggestive the moisture is beingdrawn into the space from the slate wall.The conditions behind the DL test wall are as predicted and as the moisture presentcannot re-evaporate back into the interior environment as it can through theHemp/Lime, it must penetrate the thick stone masonry in order to escape, thusincreasing the risk of frost damage to the masonry, interstitial rot and mould growth.4.1 Embodied CarbonTables 1, 2 and 3 in figure 5 summarise the embodied carbon calculations for hempcrete7