Blower Door Test “Passed!”

Sawkill Passive House passed the critical passive house blower door test on Friday, conducted by David White of Right Environments, working with Castrucci Architect and Blueline Construction. The house passed within just 1 CFM (Cubic Foot per Minute) of the test standards cut-off – a cliffhanger by building energy standards. Two days earlier, the reading hovered three points higher and out of reach. At that time, all the scouring for micro-leaks in the envelope of the house seemed exhausted; window gaskets were tightened, ventilation hoods tuned, electrical penetrations plugged; each step circling closer, but still short. It was unclear what to do.

But Mother Nature stepped in. Readings can vary slightly from successive tests at the same site. Within that natural range, it is also possible that varied weather conditions account for the difference. As they say, “You can’t step in the same river twice”. On Friday, with lower winds and higher temperatures, the indoor and outdoor environments were unseasonably equal, and that raised a prospect for a new and passing measure. David thought it was worth a try.

David White lives down the block from Prospect Park, and about a fifteen minute bike ride to 158 Clifton. His retro-fitted eight foot bicycle could haul the morning produce of a restaurant, but it’s more regularly strapped down with equipment from “Minneapolis Air Blower”. The bike and its cargo are easily managed by the 6’2” cyclist.

The air blower apparatus is a simple device – supported by a mountain of research. It pressurizes the entire house, but outside of a fan humming, you’d never know the blower door test was even happening. Within minutes, a computer registers dots along an axis; and then it stops for a moment, and the fan is flipped around, with air removed; and de-pressurizing, resulting in an average reading from multiple points of the  building envelope. If there are ghosts in the Victorian era row house, as an older resident on the block claimed early on, they would have certainly caught wind of the air blower test.

The computer graphic – a grid with round and square dots – often tells the story. But it was too close to call on Friday. David clicked through to the precise numerical data and paused, searching the numbers and then said “we passed.” It was just one-quarter-of-one-percent within range, and that was enough.

If it wasn’t. the alternative – which could have produced a passing number for the house months ago – was to “pressurise the neighbours”. This involved setting up similar systems that would flank the row house with pressurised volumes, and act like a headwind against microscopic air loss. Pressurizing just one adjacent house would blow the door off the standards firm threshold, lopping off 100 cfm’s, and it would be completely within the bounds of test procedure. But it was a last resort, and the neighbours of course were already a help, simply living with a party wall in a row house.

The Passive House Certification process prompted a systematic check for air and energy leakage, and a fine tuning process of actions, and it added up to real performance gains. But it was the attention to detail in the construction phase that made the difference. Going back to the bones of the 1880’s building, the old growth softwood joists; each was retained and sistered, and then subject to a thoughtful sealing sequence, with ‘no turning back’. Any energy leakage would be locked in, maybe for generations. All along the way, similar issues were encountered in a structure that was “….in as bad shape as any that I’ve encountered.” said Jim Hartin of Blueline.

Castrucci, Right Environments and Blueline have transformed an old building into one that is, 130 years later, in as good shape as any they’ve encountered. The PHI energy numbers alone may back that up.158 Clifton may also be a first wooden row house to reach certification in New York, and is part of the growing movement to retro-fit across the city.

As David was breaking down the blower door, he noticed one small part of the unit unclamped. “Hmm, that could have been another cfm or two.”

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