Farm Building Conversion using HempCrete

Our work has created an envelope of hemp that has given us a lovely comfortable home which requires very little extra heating; using our wood burning stove or warm air supplied by a ground source heat pump which also provides hot water. We chose timber windows with argon-filled double glazing. The Velux roof windows are triple-glazed. We also installed a mechanical ventilation and heat recovery system (MVHR). We have found that room temperatures do not fluctuate greatly and condensation is minimal even in the kitchen.

Case Study

We started investigating the use of hemp in the renovation of brick and lime buildings in 2008 and contacted Ralph Carpenter, who at the time, probably had the most experience of hemp building in England. This gave us the confidence to go ahead and renovate our own redundant brick and lime farm buildings using our home-grown hemp. Ralph suggested that we add hempcrete to the exterior of the building to preserve the internal space and also construct a 450mm solid hempcrete wall around a light timber frame for the new build element. We then began the ten-month battle to get planning approval for the change of materials. Members of the Planning Committee were aware that more planning applications would specify the use of sustainable and renewable materials and they needed to act positively.

At last, we were able to make a start using hempcrete. We have worked closely with Mike Turner, a local builder, and together we researched lime in all its various forms to enable us to decide on our formulas. We then prepared the buildings to enable us to apply 200mm of hempcrete insulation to the exterior of the brick walls. We fixed wooden pegs into the wall to act as a key for the hempcrete and also to attach the shuttering, using adjusting screws. We were now ready to mix HempBuild and lime binder in a pan mixer.

Part of the project required replacing walls and here we used shuttering to build a new 450mm thick hempcrete wall around a light timber frame. All exterior walls have been rendered with a plaster consisting of HempBuild-Fine, lime, and sand. No pigments have been added to the final plaster coat leaving a completely natural colour. Roof joists were filled with 300mm of dry hempcrete mix to make a “warm roof”. This was covered by a breathable membrane and finished with local pantiles. An overhanging roof gives protection to the walls from the weather.

We built a circular shower cubicle, within a bathroom/wetroom, using the shuttered hempcrete system we formed the wall with flexible plywood curved around a light wooden frame. This method could easily be employed to make any curved wall. The walls of the shower area have been plastered with Tadelakt – a Moroccan plaster. The surface was polished using a special ceramic stone and waterproofed by applying olive oil soap. A sun pipe increases the natural light inside the shower room.

In one corner of the kitchen, we have built a small room – 1-metre square – also fully insulated with hemp. We have added an air conditioning unit and shelving to create a cool food store/fridge.

Partition walls and ceilings have been formed using Celenit breathable wood wool boards. All the joists between the floors and the cavities in the internal walls have been filled with dry hempcrete insulation /roof mix, which also helps sound insulation in upstairs rooms.