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January 07, 2015

Proof Negative (Pressure)

Tuesday brought nervous excitement - we tested our building air tightness with a blower door test.

Basically we pressurize the house with a big fan and measure the amount of air it can continue to draw through the house.

So much attention was put into the construction - careful taping, sealing, and gasketing - how did we do?

2.1 Ach50 (Air changes per hour at a pressure of 50 pascals)

Pretty Good, but not spectacular.

As a reference point,
Energy Star Homes for Portland and Earth Advantage is < 4.0 (fair);
Passive House is < 0.6 (really excellent).
Lower the better.

I'm a little disappointed.  But...

Our performance will get much better by the time we are done:
  • This prelim test identified leaks in the envelope that we can now address.  
  • Drywall, not yet installed, will provide a significant increase in air tightness (some people rely on drywall alone for their airtight strategy).
  • Realized afterward that we didn't even cover the dryer vent.  So there was an open 4" hole to the exterior included in this test result.  That'll make a difference.
Pressurizing the house was very interesting exercise - you could feel for air leaks with your hands.  A smoke pencil is another good tool for seeing the airflow.

Chief among the leaks were the skylights.  My roofer insisted that the skylight gasket would form a great seal, and that a secondary caulk seal would only make future replacement a pain.
Well, the air was literally whistling through the gasket in a nice breeze, so an additional sealant bead is forthcoming.

Also on the list was about 1/3 of the operable windows.  Of these, a significant draft was detectable in a window corner where the gasket wasn't quite doing the job.  Due to budget reasons, we chose "good windows", but not "passive house" windows, and this illustrates the difference in gasket performance.  We believe that with some hardware adjustment, we can mitigate the worst of the issue.

Lastly, most of the doors have been replaced with temporary construction doors to prevent damage from workers.  Thus, they have no perimeter gaskets in place.  We taped over the perimeter gaps for the test, but each of the hinges weren't taped and air passed through them noticeably.  In the future, this issue should be addressed by the continuous door gaskets.

Better numbers in the future, I'll wager.








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