as previously discussed, a BIG performance component of this house is tightness. most (all?) design and constructability decisions have been founded upon the principals of building shell tightness. these include walls/roof (SIPs), windows, doors, foundation details, etc. the basic idea is to build the house as tight as possible to keep that precious (costly!) heated air INSIDE. of course, in so doing, we must also be cognizant of occupant health. if it’s too tight, then we can induce indoor air quality problems (moisture, pollutants, etc.). the catch phrase is “build it tight, ventilate it right”. what follows is some info on the “build it tight” part. more to come on the “ventilate it right” part….
in addition to design and attention to detail during construction, we must test ourselves. that’s where the blower door comes into play. basically, a blower door is a door that blows air out of the house thereby creating a negative pressure inside (it can also blow air into the house, thus creating a positive pressure, used mostly as a diagnostic method). WARNING: what follows will go some distance down the “building science” road, but NOT all the way down that road – three reasons. 1) i’m an architect, not a scientist! 2) the purpose of this blog is to present a wholistic presentation of the design and construction of 363HOUSE. 3) due to #’s 1 & 2, i’m trying to keep the information mostly accessible to the non-greengeeks amongst us!
the blower door is equipped with a computerized manometer to measure air pressure. the industry standard is 50 Paschals (50Pa) – a Paschal is a unit of measure like inches of water column. it’s been described to me as the equivalent of a 20mph wind blowing on all exterior surfaces (roof, walls, floor/foundation) of the building simultaneously. the manometer reading is rendered in Cubic Feet per Minute (CFM). the lower the number, the better. that CFM number is factored to obtain so many Air Changes per Hour (ACH). again, lower is better. so, basically, the resultant calculation tells us how many complete air changes will occur in 60 minutes at 50Pa. so, that’s interesting, huh? if you’re still reading this, then you might be wondering, “well, how many (or, few) is good?”. here’s a VERY brief primer….a reasonably, well-constructed home of “conventional/non-airtight” construction might be 15ACH@50 or more; under the 2009 International Residential Code, ≤7ACH@50 is required; an EnergyStar 3 house, ≤4@ACH is required; PassivHaus, the uber-standard for TIGHT construction, ≤0.6ACH@50 is required!
our energy model (see “energy” posted WAY back on 13 june 2012!) is based upon 1.5ACH@50Pa. we chose this target based upon previous experience and knowing that this project has many goals and a budget. so, the thinking was let’s not over-reach on every goal. nonetheless, we have been OBSESSIVELY attentive to tightness with every intention of smashing our energy model goal!
so, how’d we do????
frankly, we did NOT smash our goal. yes, we did better than 1.5 by a little more than a third. and, this is only the building shell blower door test (we can work toward improvement before the final blower door test at completion). so, i’m satisfied with our work, but not ecstatic – no chest-pounding! of course, the shell blower door should be considered a diagnostic tool – a learning opportunity. yeah, so, what did we learn????
well, our uber-tight entry doors aren’t so uber! the good thing about the uber doors is the hinges are nearly infinitely adjustable and we think we can tighten up the door seals through hinge adjustments. we also found a few small breaches in the SIPs shell incurred by some electrical wiring (MORE spray foam!). and, we have a few very minor leaks at window installation clips. the uber windows are indeed uber – no air leaks there!
BTW, leaks are discovered through the use of a smoke pencil. it’s just what it’s called, a “pencil” that emits smoke. if the smoke leaks out of the building, then that means air is going out, too! pretty cool, VERY effective, LOW-tech device!
one final thought. i’ve always found the best way to think of this whole air leakage thing is in terms of “how big of a hole does this ACH@50 number equal?”. think of it like this….if we added up the area of ALL the holes in the building shell (shell area = 5667 square feet), then the total would equal a 6″ diameter hole.
we plan to re-test in the next week, or so, after the above listed remedies have been employed. i will report any improvements worth noting.
now, if i can just GET THE ROOFER TO SHOW UP!!!!
ps: here are the calcs, for those number freaks amongst us….