The Langley Passive house is a ‘split-insulated’ wall assembley pioneered by RDH Building Engineering for the BC climate. This strategy is described in the Building Enclosure Design Guide (HPO 2011) and Guide for Designing Energy Efficiency Building Enclosures (FPInnovations 2013) both by RDH. The wall design borrows from the North Shore Passive House in construction by the Econ Group (http://www.econgroup.ca/north-shore-passive-house/) and progress photos of the North Shore home are available at http://www.econgroup.ca/north-shore-passive-house/.
The schematic roof – wall – foundation diagram shows the component parts for the Langley Passive house. The wall assembley consists of a 2×4 structural and service wall with a plywood vapour barrier at the exterior. An air barrier is taped to the rigid plywood backing. Two layers of rigid roxul provide exterior and continuous exterior insulation which in turn is held in place by 2×4 strapping on flat anchored with long screws.
The roof assembley consists of a truss roof with OSB vapour barrier attached to the underside and a 2×4 drop ceiling for services. Blown in insulation blanket the attic space.
A raft slab concrete foundation sits on 2 layers of rigid insulation which abut the rigid roxul of the wall assembley ensuring continuous insulation without thermal breaks.
The Langley Passive house is currently largely framed with roof membranes in, rigid roxul and wall strapping mostly present, and raft slab foundation installed and backfilled. The image shows the blue roofing membrane on the lower granny suite, staging is shown, double layer of rigid roxul at wall, 2×4 strapping, and south facing sunshades at the right-side of image.
The chosen assembley is a relatively vapour open system allowing any moisture that finds its way into the wall from condensation or through gaps in the assembley a way to dry out. The plywood vapour barrier has a permeance range of 115 – 252 ng/Pa*s*m2 above the prescriptive requirement of 60 ng/Pa*s*m2 (BCBC). This in addition to the vapour open air barrier and roxul insulation allows for drying to the outside. Similary the roxul in the stud wall cavity allows for drying to the inside. This contrasts with the relatively vapour closed passive house systems such as structurally insulated panels (SIPS), closed cell spray foam, EPS or XPS exterior wall insulation, and to a lesser extent systems using a traditional poly vapour barrier. The team including the passive house consultant Dale Mueller have chosen this strategy to best contend with British Columbia’s temperate rainforest climate.
Subsequent posts will go into more detail regarding the roof – wall- foundation assembley, exterior window and door installation and their construction sequencing. There are some nonconventional methods used in the all these areas which may be of special interest