There is no doubt that using biomass bound with low-carbon binders to build truly sustainable, carbon sequestering buildings is an exciting goal worth pursuing.
I was impressed early on by Lime Technology UK’s approach to building walls and roofs where the hemp-lime mix is cast around the frame creating a composite structure, not unlike reinforced concrete. They used the Tradical shiv and binder formulations manufactured by L’Hoist. There is no doubt that Tradical is the most consistent, best-understood formulation on the market. The way Lime Technology UK applied it to create 200 – 300mm walls ensured a consistent, insulating mix that dried well.
I’ve also looked at various alternatives mixes for numerous projects in Ireland and at one stage facilitated the construction of a hemp-magnesium test cell in my own garden. I realised with time that most formulations varied too much, were not supported by scientific testing, were not mixed consistently on site, and during construction were tamped too densely with too much water. As a result drying time and water content often appear to be a problem, which can also lead to the development of a pungent smell: all the things that might put a member of the public off using biocomposites in their home project.
I was delighted to come across Simon James Lewis’s approach to casting hemp-lime internal wall insulation using Tradical ‘roof mix’, with a lime plaster finish. Being a roof mix it is a lighter, drier (non-structural) mix. I was very impressed by the rigour of the measuring process, ‘cooking’ as it were with exactly the right amount of the ingredients and the prevention of over-tamping. I thought the use of traditional timber ‘dooks’ cut off true, with the aid of a laser level, to create the supports for small shuttering boards, the insertion of timber grounds to take fixtures, and rounded timber rails to strengthen corners was a really interesting re-interpretation of historic carpentry techniques to a new purpose.
The use of glue-size and wallpaper as a wall finish with very high moisture buffering characteristic (contrary to the synthetic paints and vinyl-backed wallpaper which home decorators are often encouraged to install) supports the breathable nature of the H-L ‘roof mix’. I can well believe the resulting assembly has a beneficial sanitary effect on the internal environment.
“It is undoubtedly the best hemp-lime application I have seen in several years. It is also one of the best wet-applied, breathable solid wall internal wall insulation systems I have seen, yet I believe it may be one of the cheapest. Well done Neighbourhood Construction.”
Assessing risks in insulating retrofits using Hygrothermal software tools. Heat and moisture transport in internally insulated stone walls.
Historic Environment Scotland Technical Paper 15
Joseph Little, Calina Ferraro & Beñat Arregi
Having visited a number of installations of this type, my initial impressions are that the system improves thermal comfort for occupants in three main ways.
Insulating solid-wall houses using plant-based materials
Dr Judith Thornton