For these three individual houses and replacement side-additions to a Victorian dwelling in Dulwich, south London, we had to satisfy certain projectspecific performance criteria. We wanted to minimise the impact on the neighbourhood by the speed of construction and to limit the construction processes by introducing multifunctional components. Within a construction strategy of producing all building components off site, we explored the geometrical limits of two products: LenoTec from Finnforest Merk and Holzbau Berchtold, an Austrian product.
Holzbau Berchtold is commonly known as Moon Wood and is more famously used in the production of musical instruments. The timber is farmed biodynamically; it is harvested according to the lunar cycle - at a point at which the sap has largely retreated to the roots - in order to produce a more aerated product. The advantage: it can be used to form structural facades achieving great U-values with no need for additional insulation; there are no cold bridge issues because the panels are dowel-jointed without the need for glue. The disadvantage: it is currently prohibitively expensive.
Our preferred facade system, LenoTec, uses a bi-axial timber panel, wood-fibre insulation and a rainscreen. It can be used with no extra insulation.
The material used is thicker and consequently more costly and heavier; however, it has greater thermal mass and can improve the construction time and complexity through limiting on-site processes.
LenoTec is produced using off-cuts from the production of softwood planks. The outer edges of the cut trunk are normally converted to MDF, which has high glue content or chipboard that has a low structural performance. LenoTec uses just 2 per cent glue by volume and although the product gives off formaldehyde (as does timber), we are assured that the gas is gone by the time the product is on site.
Setting targets for configuration of the Fountain Drive houses, panels can be constructed up to 14.5m x 4.5m and can be curved. However, the normal transportable panels are restricted to 4m x 9m or 3m x 11m. Using prefabricated pieces to the maximum size reduces costs in connections. Complex abutments can be created as required, such as where panels come together to form the roof.