When setting out to build an efficient house, the elephant in the room is air tightness. Industry is resisting mandated air tightness testing if thresholds are introduced meanwhile building codes are ratcheting up efficiency on all fronts except air tightness. Having debunked the myth that “a house needs to breath” its becoming painfully obvious to any building scientist that the lowest hanging fruit on the efficiency tree isn’t geothermal but simply producing a more air tight home. You'll have to do it eventually, why wait and make homeowners pay more for heating and cooling their homes? Not testing your builds just reflects badly on you and your reputation.
No stranger to regular air tightness tests pre or post occupancy, Ed Marion shatters his air tightness target and is being congratulated by Shervin...again.
Our field testing on new homes show that even new homes can be super leaky, in fact as much as 7 Air Changes Per Hour at 50Pascals*. To put that air leakage rate in perspective, the sum of heat lost in winter and summer humidity let in by air leakage will be greater than the energy lost through the entire wall surface area. It begs the question, why spend more on an iota of wall insulation when the house is so leaky? Adding insult to injury these homes typically all have Heat Recovery Ventilators installed and this device requires an air tight house to earn its keep.
Don't be scared...
The heart of the matter lies with potentially "failing" to make the air tightness threshold and what that might mean to scheduling issues in production or profit loses that might occur, but in our experience, the fears are overblown. The costs are negligible if the testing is done at the right time, beside once a builder sees where the leakage takes place, they typically don't make the same mistake twice. This brings us to the crux of this blog; if you could invest in only one air tightness test; pre-drywall or pre-occupancy which would be more crucial?
Hands down, the pre-drywall test is the best stage to have your house tested so that a) you can adjust what you’re doing on future builds and b) you can remedy the problem. In our experience, repairing air leaks before the drywall is up usually stacks up to less than a half day of labour and less than $50 in airsealing materials. That’s low cost and low risk for significant benefits like reduced call-backs and the potential for situations like an “ice dam” or mould in the attic or humidity driving into the envelope.
"What could possibly co wrong?" A pre-drywall blower door test would have saved this homeowner $10G to fix the problem. The above clip isn't from a roof leaking rain, this is condensation. In this 3rd floor attic of a $1.7million house built in 2013, 'Stack Effect' drives moist conditioned indoor air up through pot lights and a pocket door and into the cold attic. The moist air condenses on the aluminum of the roof vent and drips on the attic floor and into the master-bedroom ceiling. Note municipal inspectors check to see if the house meets the minimum standard; they don't check for air leakage and don't assume that spray foam gives you immunity either.
Everything is pointing to higher efficiency and to build a house that’s leaky is just too much of a risk. The next code cycle are going to raise the bare on envelope R-values and mechanical efficiencies not to mention the fact that the way we calculate heat loss (F280) in buildings starting in 2017 will include the option reduce the air leakage rate from 4.8 to the lower leakage rate you plan to build your house to**!
*The homes in question were tract-built, town homes being built in 2013 in Brampton slated to be ENERGY STAR® which has a maximum of 2 ACH50. Stunningly, most of the air leakage was from the garage - think carbon monoxide in the living room. Let’s just say, it’s a good thing they investing in pre-drywall blower door tests so that they could remedy the air leakage in order to make the ENERGY STAR® grade. 7 air changes per hour puts this house with a weatherised 1920 uninsulated house.
** For perspective, we’ve tested new homes with air leakage rates lower than 0.5 ACH50 and renovations of 50 year old homes to less than 0.6 ACH50 and 100 year-old brick homes to less than 2.0 ACH50.
*** Offer valid if booked before June 1, 2014 and may be subject to geographic restrictions, call for details.