The walls and floor
With the underpinning, foundations and floor slab complete, the next task on site is the construction of the walls. The existing walls of barn A are of brick construction, approximately 330mm in depth. Various options were investigated for the new walls and in the end it was decided to construct a cavity type wall. The existing brickwork is retained as the outer leaf then there is a 250mm wide cavity fully filled with insulation and a 140mm inner leaf built in thermalite blockwork. On the inside of this is a wet plaster finish which also acts as the air barrier. In certain places there will also be a layer of timber battens to create a service cavity. Below is a typical base detail showing the wall and floor junction.
Passivhaus, Dulwich Estate
The walls are to be insulated with Icynene spray foam insulation. The open cell insulation will be sprayed into the cavities at various stages as the walls are built up. Teplo low conductivity wall ties are used to tie the new inner leaf of blockwork to the existing brickwork. These are resin anchored into the existing brickwork. At the base of the walls a course of Foamglass insulating blocks are used to break the thermal bridge between the warm inner leaf and cold foundations in the ground. The wall u-value is 0.11 W/m2k. The floor is made up of a concrete slab with a self adhesive gas resistant damp proof membrane then 225mm of phenolic type insulation. On top of the insulation is an anhydrite flow screed, which has a high thermal storage capacity. The screed also acts as the floor air barrier. The junction between the wall and floor is sealed with propriety air tightness tapes. There is also an perimeter channel around the floor for services, making future changes easy and accessible. The floor u-value is 0.125 W/m2k. Below are some photos of the installation of the first lift of Icynene.