Passive House in Boerum Hill

In our third Boerum Hill townhouse renovation, we are applying Passive House principles to transform a derelict single-room occupancy townhouse into an energy-optimized machine for family living.

The core principles of the Passive House standard are rather simple: insulation, air-tightness, and removal of thermal bridges.  In order to achieve this though, we must take our material specifications and weather-proofing details very seriously, and the contractors must exercise the utmost care in creating a building envelope that can pass the blower door test, which quantifies the house’s performance in terms of air change frequency.

Insulation requirements dictate that we insulate beneath the house as well, so we took this opportunity to excavate the cellar another four feet, allowing for vastly increased overhead clearance.  The sealed and insulated slab and foundation will ensure that the cellar stays warm and dry in all seasons.  In addition to expanding downward, we are expanding backward: a new rear extension of two lower levels will house generously-sized exercise and dining rooms.  Although the extension is a fully contemporary structure, Passive House methods will ensure that there is no perceivable difference between the thermal performances of the two parts of the building.

Generally speaking, windows and doors are areas of significant thermal bridging and air leakage (which can sometimes be useful when trying to gauge the outside temperature by touching the glass on the inside of the window), but Passive House windows are so well sealed and insulated that they give no indication as to the temperature differential between inside and outside.  The image above, taken with a thermal camera, illustrates the difference in heat released by a Passive townhouse as compared with surrounding traditionally-insulated townhouses.