The external wall cladding is of vertical Accoya tongued-and-grooved strips. Accoya is acetylated timber. The patented treatment is carried out in Holland.
Its effect is to change the cell structure of the wood: instead of being open to absorb and give up moisture, leading to movement and then disintegration, the cells are closed and so movement is very much reduced. This means that the manufacturers can offer a 50-year guarantee of its integrity, whether it is painted or not. Our original intention was that it should be pre-painted, but the client opted for it to be unpainted, understanding that it will go grey and stain unevenly, since the façades are not designed for uniform exposure of the timber cladding. The timber used in
Accoya is radial pine, largely grown in New Zealand, so transported by sea. However, it is a timber too poor for normal use without the Accoya treatment, so the net effect is to make good use of an otherwise unused resource, again using a material with high levels of sequestered carbon. The planks are generally secret fixed to battens and counter battens, themselves fixed through the 200mm PIR Celotex XR4000 insulation to the CLT inner leaf.
The roof cladding is of pre-patinated zinc, site fixed with folded welts, onto plywood on insulation. The rainwater goods are also of zinc, all supplied from France by VM Zinc. The windows are Velfac (the only UK supplier among those mentioned so far), so have timber frames with ppc aluminium externally.