The aggregate fill for the foundations was all slate from the CAT site. Parts of the site had bedrock (a low grade slate) that needed to be removed, and this provided sufficient loose aggregate to create a level site. Slate from a demolished old quarry building was used to build the walls of the courtyard, and as we didn't have slate on site suitable for the decorative facing on the plinth walls, this was brought in from Blaenau Ffestiniog.
Sand lime (calcium silicate) bricks were used to construct the plinth walls that support the frame. These are autoclaved (cured in pressurised steam) instead of being fired, which means they have a lower embodied energy than standard clay bricks. These bricks are affected by moisture and will expand and contract. To ensure they would work for WISE, we incorporated carefully designed movement joints and used lime mortar (itself flexible). With hindsight, due to the number of bricks involved, it would have been faster, and so more economical, to use some form of block work - but at the moment it is difficult to find an environmentally sound alternative to conventional blocks.
The brickwork forms a cavity wall filled with perlite to provide insulation. The top few inches was mixed with limecrete (see below) to provide a cap to the wall. Perlite is a volcanic rock that ‘puffs up’ when heated to high temperatures. As well as insulation under the ground floor slabs, it was used in some walls and ceilings.
At CAT, we avoid the use of cement as much as possible, due to its very high embodied energy. Instead, we’ve mainly used limecrete, which, though not as strong, is more than adequate for many situations. The limecrete mix used shale aggregate from Wenlock and sand from Condover Quarry (both in Shropshire), with St Astier lime. We wanted to use recycled aggregate, but CAT is just too far from major built-up areas to be able to source them readily.
Ground bearing slabs in WISE were constructed of hempcrete, a material that uses a lime based binder with hemp shiv, laid on 200mm of perlite insulation, used in bags. A vapour control/radon barrier is supplied by a recycled polythene membrane ('Zedcore'). Floating floors are laid onto all floors (including suspended floors). All have a layer of 'Silencio Thermo' grooved softboard to hold underfloor heating pipes. The floor is finished with a proprietary floating floor with plywood and looselaid, secretly nailed, ash floorboard.
The raft foundation had to be ordinary concrete reinforced with steel to achieve the required strength and stiffness - as did the raking foundations that went up the side of the slate tip. Raft foundations spread the building load over a wide area and are stiff enough to withstand some movement of the underlying ground; unreinforced concrete or limecrete would crack in this situation. We have been able to drastically reduce the embodied energy where we have had to use concrete, by substituting 50 per cent of the Ordinary Portland Cement (OPC) for Ground Granulated Blast Furnace Slag (GGBS). This is a by-product of the iron and steel industry and used to be considered waste, but is now a quite common substitute aggregate.
Traditional fired clay pipes have been used for ducts and drains, instead of PVC pipes. We avoided using PVC because it has a high embodied energy and causes other pollution problems during manufacture and disposal.