from the ground up - The Tyee

solid spruce provides thermal mass that helps hold thebuilding at a consistent temperature.“This inside wall, the four inch mass wall, is yourstructure,” Dürfeld said. “The rest is just a blanket.”Layer two: Plywood vapour barrierWhere Canadian builders place large sheets of plasticbehind the drywall, the Austrians mount yet anotherlayer of wood.Austria House’s vapour barrier is built of plywood.Where one sheet of plywood joins the next, the seamis carefully taped.“They have amazing tapes,” Dürfeld said. “We haveone tape we’re all familiar with, the red stuff. Theyhave different tapes for wood-to-wood, for wood-toconcrete.They have about five or six different tapes,depending on the product they are taping.”And while Canadian vapour barriers are typicallypunctured every few inches by staples, drywall screwsand junction boxes, Passivhaus vapour barriers aresacrosanct. Wiring and plumbing is run inside the barrier(in the sold spruce wall), not through it.“When we build dimensionally, we tend to penetrateour vapor barrier everywhere. A typical home probablyhas three to four hundred penetrations in itsvapour barrier,” Dürfeld said.Not surprisingly, such buildings are not even close toairtight.When subjected to a blower door test, which is designedto create a pressure difference of 50 Pascalsbetween the interior and exterior air, a typical Canadianhome might measure between four and sixair changes per hour. (This is described as 6 AC/H@50Pa.) That’s not ventilation; that’s just leakage.The R-2000 standard to which BuiltGreen homesaspire is 1.5 air changes per hour at the same pressure.The minimum Passivhaus standard is 0.6 air changesper hour.Austria House rated only 0.26 air changes per hour.“This is probably the most critical component,” Dürfeldobserved. “If you fail air tightness, you’re simplynot going to get the rest of it right.”More layers, more woodThe Austrian fetish for wood products extends to theouter layers as well.Beyond the vapour barrier, where Canadian homebuildersinstall 2x6 studs (aka. thermal bridges) andfibreglass batt insulation, the Austrians install 2x12sand non-toxic insulation such as blown-in cellulose (awood product) or mineral wool.“The preference over there is for wood-based insulation,”Dürfeld said.The outside wall, where Canadian builders install yetanother layer of plastic (such as Tyvek), the Austriansmount what they call defusion board.“It looks like fiberboard. It’s denser than a donnaconna. But it can pass vapour,” Dürfeld said. “Again,it’s a wood-based product.”In Northern Europe, a (wood slat) rainscreen is attachedto the diffusion board, and (typically wooden)siding is mounted on the outside.The Whistler house, however, is clad with distinctiveblack cementations siding similar to Hardiplank. This,too, was provided by one of the building’s sponsors.Windows that shut tightWindows are a notable exception to the Passivhausstandard’s performance-based approach. This is becausethere is virtually no possibility of meeting thePassivhaus air tightness requirements with the relativelypoor quality windows sold in North America.“The windows are absolutely key,” Dürfeld said.“That can be the biggest heat loss in your house.”In Europe, the Passivhaus standard specifies windowstested and registered by the Passivhaus Institute or affiliates.These windows are typically constructed fromthree panes of coated glass separated by two gas-filledchambers, each of which is more than a half-inch45