Page 32 - CodeWatcher Winter 2017 Issue

Better Than Code

Once Isn’t Enough

Are HERS raters missing the mark by not insisting
on two blower door tests?

TBY AL COBB Blower door tests allow builders to pinpoint leaks that need attention.
HE HIGH-PERFORMANCE construction
industry relies on various tools to quantify We should strive to make durability a keystone of all builds
levels of efficiency. One of the most and that is jeopardized when moisture-laden air is allowed
common is the blower door test. Not only to leak uncontrolled in or out of the building envelope.
does the blower door test help to verify Airtightness is as vital as proper mechanical ventilation and
code compliance, but it also confirms the both should be part of a building strategy.
level of airtightness defined by many of the
point-based certification programs. The blower door test can As a high-performance builder, the blower door test is
also be used to fine tune the accuracy of energy modeling. my best friend. On my SIP builds a blower door test is more
However, in my experience the greatest benefit of a blower than just a check box. It’s an opportunity for the whole crew
door test is quality control. to learn and for me to find which of the subcontractors have
or have not met the high bar of airtightness.
Most builders and raters schedule a test at the completion
of the project, usually because of code requirements or When my HERs Rater pulls vacuum on an envelope
certification program verification (EnergyStar, Passive it becomes a game of finding the leaks and challenging
House, etc.). When building my first Passive House in 2010, I ourselves to push the envelope of airtightness (pun intended).
guaranteed my company would meet the mandatory metric Finding a leak forces us to ask the obvious questions:
of less than .6 ACH (air changes per hour) @ 50. This metric is
easily achievable with a superior envelope system, a quality ¦¦ Who installed the panels in this area?
conscious installation crew, and a plan. ¦¦ Who sealed this section and how?
¦¦ Who drilled this hole and left it unfilled?
Ask most high-performance builders when they schedule ¦¦ Can we pinpoint the exact location of leakage?
the first blower door test, and they’ll usually respond: “After ¦¦ Does this detail look good on paper but fail in the field?
the envelope is sealed and pre-drywall”! If a single test is
performed at the conclusion of the project and fails to meet
that metric, you’re in trouble. It should be obvious that post-
drywall makes additional sealing or correcting improper
sealing difficult, if even possible.

Testing a finished house may provide an accurate number,
but tracing the sources of leakage is often misleading when
drywall and cladding can hide the actual hole that needs
plugging. A blower door test before both interior and
exterior cladding/finishes is essential to ensuring the access
needed to pinpoint leakage and make repairs that result in
a successful ACH number.

Durability At Risk?

As important as high performance is in construction, I place
durability on an equal level. What good is a lower utility
bill if your roof is slowly deteriorating from accumulated
moisture?

32 CodeWatcher / January 2017 www.codewatcher.us