Project details

Broadhempston, Devon

Straw Bale Affordable Housing, Devon

“Low Cost Self Build Houses for ‘Low Impact’ living”

This project arose from a competition submission, where we designed adaptable, low cost, timber frame and straw bale ‘house types’, from which we could test the feasibility of the units on rural sites around South Devon.

We were subsequently commissioned to design 6 simple, low cost, low environmental impact, self build affordable housing for Broadhempston Community Land Trust (CLT) based on our straw bale house types.

The site was a rural field on the edge of the village, outside of the development boundary. Planning Permission could only be achieved by demonstrating the land as an ‘exception site’, where high quality design and 100% affordability were crucial planning criteria. The work of AK.A and BCLT won the support of Teignbridge District Council, who now use the project as a pilot for their regional affordable housing programme.

The ‘exception site’ status allows for the development of land, not otherwise permitted in planning policy, but opens up low cost rural land purchase opportunities for affordable housing, in partnership with ‘willing landowners’, who support their local community and needs.

In the delivery of the project, this was a very exciting opportunity for us in using our specific skills for low energy design, environmental design, use of natural materials (straw bale) and integration of renewable technologies. However, the wider challenge of this project was to work with the community group and help mitigate the risks in the delivery of a self build project on site.

This was ultimately achieved by setting up a management structure, where we ‘sub contracted’ in specialists for the high risk items such as the groundworks, infrastructure, services and structural frames. The remainder of the works considered as lower risk, were delivered by the self build group. This structure achieved a 25% ‘sweat equity’ ownership of the houses by the self build residents.

The design is modest and simple, but aims to make the most of passive solar orientation with unheated sun rooms. Materials were selected to have a connection to their surroundings.

The construction methodology was based around a lightweight and cost effective timber frame, which would be erected by a timber frame company and super insulated by the self builders using locally sourced straw bale insulation.

Costs were, of course, critical to the whole process. Our target cost per house was £80K, which was achieved. At 120sqm per house, this equated to an exceptionally low cost/sqm rate. The overall costs per house including land costs, fees, infrastructure and utilities completed at £150K per house.

The wall and roof design achieves U values (heat loss) far in excess of current building regulations requirements, and even exceed passivhaus standards where notional U values are considered through the building fabric. However, it should be said that overall passivhaus criteria are not being aimed for and a passivhaus assessment was not carried out for these houses.

Each house has a sun room. In addition to this being a useable and pleasant space where food can be grown, it also helps to heat the house and distribute passive solar gain in the colder months through to other areas of the house. The houses will require very little additional heating, but where required, hot water and space heating is provided by biomass, PV solar panels and heat pump technology.

Underpinning all of these principles is the motivation of the community to keep pushing forward with this project and take the procurement of their homes into their own hands.

This is an important community ownership scheme, which is delivering a powerful ‘Social Impact’ message by not only providing affordable housing to local people, but achieving standards of design and energy efficiency far in excess of that which you would normally find on the open market.