Case study: Building a Hemp House
When we decided to build our house from hemp, one of the main reasons was that we grow industrial hemp and process the crop on the farm. One of its uses is for the hempcrete buildings. Hempcrete is a mix of the woody core of the hemp plant and a lime based binder; this is used to construct a solid wall around a structural timber frame. The advantages of a hempcrete are numerous. Hempcrete is a high performance, low carbon, low energy, biocompesit building material. Hempcrete is highly insulating and breathable, and these two properties do reduce the energy required to heat the house. A breathable building allows moisture to move through the walls eliminating damp, condensation and mould problems - there must be nothing in the walls to stop this flow of moisture, in a breathable building you cannot use plastic membranes, vinyl wallpaper or non-breathable paints.
We started our project in January 2013 by first knocking down the original house which was full of damp and rot. The original house had been very expensive to heat and was never warm.
The new house is built on a standard foundation to building controls requirements. Underfloor heating was installed into the ground floor prior to the concrete floor being laid. The timber frame was built by Turner Timber Frames of Hull, and was designed by them specifically for use with hempcrete. The main difference was that they had to omit the vapour barrier to allow the hempcrete to breathe, and the frame also needed horizontal laths for the hempcrete to bind to. This frame was erected in August 2013.
There are two ways to apply the hempcrete, one is to shutter both sides of your timber frame and hand cast the hempcrete in to the wall. This can be done by a contractor, or with some training it could be a job undertaken by a self-builder. The other method is to shutter only on one side of the frame and install the hempcrete using specialist hempcrete spraying machinery - this is definitely a job for a contractor. We had previously used hand-cast hempcrete on the barn conversion that we completed in 2011. We decided to spray apply the hempcrete to our new house after watching a demonstration of the technique, which we found through the many contacts we have made in the Hemp building industry. Videos of hemp spraying can be found on YouTube.
Whilst we were spraying the hempcrete we tiled the roof with eco slates made from recycled plastic. The eco slates are a lot lighter, much quicker to apply and there is no waste, while giving the appearance of a traditional slate roof. The roof on a hempcrete building needs to overhang to give protection to the walls from the weather.
While the hempcrete was drying we installed the windows and external doors. These were made by a local joiner out of hard wood as we like the look of wood windows.
The house is finished on the outside using a hemp lime render to protect the hempcrete from the weather. We insulated the roof and between the floors using hempfibre insulation, which is made from hemp fibre grown on our farm and is available from East Yorkshire Hemp. We have fitted a mechanical heat recovery and ventilation system: this system removes moist air from the wet rooms and introduces filtered fresh warm air to the living rooms giving a healthier atmosphere to live in. It also means trickle-vents are not required in the windows. We have also installed a central vacuum system to help reduce dust; these two systems benefit us all, especially one of our children who suffers with allergies and asthma. The only heating we have is the underfloor heating on the ground floor which is run by a biomass boiler in an outbuilding. We choose this system because it runs on logs from trees which grow on the farm.
The house is plastered throughout with a hemplime plaster to maintain the breathable nature of the wall and decorated inside with a breathable clay paint. We used Earthborn clay paints.
The project itself took us 2 years and we moved in April 2015. We are extremely pleased with how the house has turned out: it is bright and airy with lots of open space and warm enough for us all.
Please don’t hesitate to contact East Yorkshire Hemp if you are considering your own hempcrete build we will be happy to share our experiences with you.
Hemplime construct hand casting - www.ukhempcrete.com
Hempcrete spraying - www.hemplimespray.co.uk
Timber frames – www.TurnerTimberFrames.co.uk