RIBA & AECB join up for site visit to The Curly House.
Many of the usual faces, that form the AECB south east group, where out on a jolly last Saturday. But in addition to those regular members, we have some new comers too. The site visit was advertised online to RIBA south east members as a joint venture to help promote the AECB, and expand our circle of friends and colleagues.
The first site of two visited on the day, was The Curly House, designed by Ecotecture Architects with consultancy from Kithurst & constructed by Kithurst Builders. The design team also included BLB engineers, all three consultants are members of the AECB. The client recognised the wealth of knowledge and experience that the AECB embodies and this would have influenced the decision to appoint said consultants.
The home is located on the south downs way, in an area of outstanding natural beauty, so achieving a permission for a high concept contemporary home was a tall order. Much discussion revolved around how this was achieved and what pitfalls may come up for those embarking on similar projects. Ecotecture worked along side the planning consultants DMH Stallard in interpreting the latest (at the time of 2008) planning legislation. After an initial refusal on the site for a 2 storey development timber frame Passivhaus, the design team went back to the drawing board, and focused intently on the wording of the latest planning documents. It was acknowledged that a semi subterranean building would be required to meet the accommodation requirements of the client, whilst setting the proposal down into the countryside to become more attractive to the local planning department. The quote which the tipped the balance in the projects favor was in PPS 7; “Modern designs reflecting traditional detailing or using traditional materials, or traditional designs using modern materials, can allow building design in the AONBs to continue to evolve without losing local distinctiveness and being uncomfortable in their context.” This policy statement was key in delivering the contemporary architectural style, which was such an important feature for the client.
The challenges of producing a very low energy building which is organic in form and affordable within a highly exposed site location, started when the detailed drawing packages where produced. The project went through many iterations before a fixed construction method was identified. Antoine from Kithurst Builders described types of construction considered including; straw bale, timber-frame, timber / steel frame hybrid, I-Joists & Metal framing / lattice joists. Each of these construction methods have there benefits and inherent weaknesses. The leading factors in the decision making process where; robustness, energy efficiency and cost. For these reasons Nudura ICF (insulated concrete formwork) and OP-Deck (thermally broken super insulated deck system) where chosen to be specified within the detailed drawing package.
In terms of the structural design, the structural engineers (BLB engineers) had to be inventive with how the reinforcement was specified within the property. Building codes in the UK are recognised to be far more stringent than that of Canada, where the majority of ICF (insulated concrete formwork) systems are in common use. The UK codes call for reinforcement levels which would considerably increase cost on the project and the level of embodied energy within the building fabric. Using approved inspectors in preference to local building control, gave the design team more flexibility to reduce the need for structural reinforcement.
The two building systems produce a practically zero thermal bridge construction, and enable the overhanging brise soleil to be installed without the detrimental cold bridge that is typically associated. There where however, a few areas where the contemporary design proved challenging to achieve the air tightness standards, whilst maintaining a thermal bridge free thermal envelope. The best example of this is how the tips of the crescent are formed in the glazed structure (see detailed drawing below).
Thermal performance & embodied energy.
Initial air tests show the property achieving 0.3 air changes per hour, Antoine from Kithurst builders has intentionally surpassed the air tightness standard required for Passivhaus compliance. The front door to the property is not passivhaus compliant and is in fact an eccentric pivot door, which has inherent air tightness issues. By surpassing the Passivhaus standard Kithurst builders have made allowance for this poorer performing building element. This seems a minor detail, but this is something which should be considered when a client has a good eye for detail, and would be unhappy if the home of their dreams did not contain such an important feature.
Jake White from Ecotecture described how the concrete core within the Nudura ICF plays an important role in the balance of temperatures in the building. “When we first saw the system, we were not convinced that the product utilised its thermal mass in the most effective way. We were heavily reliant on Kithurst’s experience with the product and we are glad this is where we placed our trust. We now understand that having the core locked away from the internal environment has a positive effect on the temperature in the building. The issue with exposed thermal mass is it can quite easily cause a feedback loop, each night emitting slightly less than the amount absorbed during the daytime. Using thermal mass which is isolated in this way increases the lag between absorption and re-emission. This is great for ironing out spikes of unusually hot October weather!”
The contentious matter of embodied energy was raised a few times during the visit. This build will not sit comfortably with all involved in green building, it would seam counter-intuitive to utilise such high embodied energy products as expanded polystyrene and concrete in the delivery of an eco home. Arguments against the use of these products are obvious, discussions supporting the choices made include site appropriateness. The location of the dwelling is infamous for extreme exposure to the elements, its position on the South-downs Way can mean blisteringly cold winters and very hot summers. The choice to use a heavier construction relates to the level of site exposure. The semi subterranean nature of the design also means the use of materials which suffer from damp problems could not be considered as a viable alternative. Jake White from Ecotecture says on the subject “We consider that the investment in terms of embodied energy stacks up in this particular scenario, this home will be passed from generation to generation, with practically no running cost. This investment does makes sense to us. We cannot see what the future will hold, but I am happy that this family and it’s future generations will be unaffected by escalating fuel costs and in a healthy and comfortable environment.”
AECB South East are looking for new projects to visit, please contact (Mel Laurie) on (01444 416745) for suggestions of projects in and around the Brighton area, which would be keen for a future visit.