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

It is also clear that hemp renders will sequester carbon into the renovation wallshowever based on U-values alone a DL method will still save more carbon by fueldisplacement in the long term. However as illustrated on the large scale the carbonsaved into the hemp wall could be utilised to offset renewable energy constructionswhich will then save more carbon than just the carbon saved by the increase in thermalefficiency improving the long term carbon savings associated with hemp and limerenovations. Further the U-value is unlikely to be fully representative of the true thermalefficiency of the hemp renders as it doesn‘t include thermal bridge reduction, moisturebuffering effects or the drying of the external wall. It will therefore be interesting to seehow the hemp render behaves once it is fully dry. Therefore the main conclusions are;1. Dry Lining causes moisture to accumulate in the wall and space behind it whichwill lead to rot, internal structural damage and increased frost damage.2. Hemp renders are not only insulating but also dry out the external wall and handlemoisture well suggestive that they reduce the risk of rot, mould and frost damageovertime.3. Hemp renders sequester significant amounts of carbon dioxide which could beused to offset the embodied carbon of renewables in a win win scenario4. U-values can under predict actual performanceThe cottage will continue to be monitored and the results reported, a post occupancyevaluation is under way and further modelling work is planned to try and establish thefuture thermal, hygric and moisture buffering performance of the hemp render. All thistogether with work initiated already looking into the composting potential of hemp andbinder should allow an inclusive environmental and performance of assessment of hemprenders to be established. Finally from the results it appears that for internal renovationthat hemp and binder is a viable option that not only improves thermal performance butalso handles moisture effectively. Its wet application is a problem and creating a dryapplication from pre-formed blocks is another area of future research that is underway.6 AcknowledgementsA warm thank you is extended to the CAT volunteers Simon and Murdo who prepared theCottage for renovation, Carole for her tireless hemp and lime mixing, all the other CATvolunteers who tamped and carried the hemp into place and especially to Arthur Butler the CATengineer who was instrumental in ensuring that all the probes and data-logger where correctlyinstalled.7 ReferencesADAS (2005) UK Flax and Hemp production: The impact of changes in supportmeasures on the competitiveness and future potential of UK fibre production andindustrial use, ADASCentre for Sustainable Crop Management for DEFRA.14