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Park Slope Passive House

The new design of this house began with the old: an 1890’s two-story red-brick townhouse, with simple stone trims and fine narrow mortar joints, blessed with a south-facing rear facade and unused Zoning Floor Area. It has an exceptionally straight and sound exterior, but its mistreated interior is past repair. And, like much of NYC, it is built with construction that is the technological peer of horse-drawn transport and the telegraph.

The project goal is to revitalize the building, put its assets to use, dramatically elevate its performance, and create new value. A full new interior is obliged. The rear facade will be opened to sun and greenery. A new third floor and deeper cellar make a modest-sized house significantly larger. A rooftop clerestory window will bring sunlight nearly to the front door. The owners recognize that an investment of this magnitude is a one-time opportunity to change the energy footprint of the building, and having been compelled by the economics and performance of Passive House they purchased the property with this specifically in mind, so Passive House certification under the EnerPHit standard is expected.

As a Passive House renovation of a Brooklyn townhouse, the project faces typical challenges at which the local community has become expert. New work can’t be added over the outside of exterior load-bearing structural walls because they are party walls or were built with zero clearance to lot lines. This necessitates work be applied from the interior: a condition familiar to New Yorkers but unusual and contrary to ideal for Passive Houses. The emblematic problem is that every single joist in the house penetrates the air barrier twice, and the contractor must know or learn how to make good seals at this spot. But a number of other conditions also arise: water vapor drive in potentially permeable exterior load-bearing masonry walls is managed carefully with redundant systems and detailed, through specification of assemblies. Steps in thickness of exterior walls and the mating of new structure to existing demand consideration for thermal bridging and adjustment of convention.