The Passive House standard for building retrofits requires a blower door test of no greater than 1.0 ACH50. For this gut-rehab project on a Brooklyn, New York, brownstone, that means repointing, parging, and coating the brick party walls shared with adjacent neighbors, and then applying a continuous air-tight, but vapor-permeable "smart" membrane (Intello from ProClima) to the inside surface of the front and rear walls and the underside of the roof, and sealing the membrane to the coated brick using ProClima's Tescon Vana tape. With a foot of blown cellulose in the roof framing cavities and four inches of rooftop rigid insulation atop that, the roof will be the most heavily insulated assembly in the building. Front and rear walls are more lightly insulated, and the shared party walls, which face the conditioned space of the adjoining neighbors, require no insulation, explains Passive House consultant Cramer Silkworth: they need only an air-tight (but vapor open) coating of Sto Emerald Cote.

Read the companion article to this slideshow: Brooklyn Passive House: Sealing the Envelope