The Cost of Air Sealing — When is it Tight Enough?
Part 1: New Builds
Knowledge preface: the Canadian Home Builders’ Association defines airtightness as “the degree to which unintentional openings have been avoided in a building’s structure.” A more airtight building will leak less air, thus losing less heat (which you’ve paid for!). Think about all the joints, cracks, and holes in your home, around your windows and door frames, at vent openings, the attic hatch, etc.
When considering energy efficient construction, Energy Advisors are looking for the lowest cost and greatest savings changes. We’re trying to get the biggest bang for your dollar first, because we all know the law of diminishing returns.
We are often asked “How tight should I try to make my home?” To answer this, we must look not only at the energy saved, but also at the cost to reach that airtightness.
Energy Advisors conduct blower door tests, which measure the airtightness of a building. Through this test, the Energy Advisor can find out where air leakage is coming through the building’s envelope and can make suggestions on how to improve the airtightness.
Energy savings from airtightness is a linear relationship, meaning that the tighter the home, the more energy saved. Lower air changes per hour (ACH) within the house means that less heat is required, which saves energy.
Costs of Airtightness
Looking at that graph, you could say, “You might as well just make the home as tight as possible.” However, that statement fails to consider that there are increased costs of making the home tighter. Following that pesky law of diminishing returns, there is a higher cost for a more airtight building that saves energy.
How far should you go?
For new homes, 3.2 ACH is the default air tightness, 1.5 ACH is tight, and 0.5 ACH is very tight. In our experience, 0.2 ACH is the tightest house we’ve ever seen! It’s important to note that none of these numbers are ‘magic’, they’re just targets set by industry.
You (or your Energy Advisor) will have to play with the numbers a bit, but in general spending an extra $500 to air seal a new building makes sense with the cost of future energy savings. If you’re at a lower ACH, it might even make sense to spend $2,000 to seal to an even lower number (such as 0.5 ACH). However, it isn’t as economical to spend $500 to reach 1.5 ACH and then spend another $2,000 to reach 0.5 ACH.
These numbers are only an example, but they show the importance of using energy modelling and good costing. An experienced Energy Advisor is an amazing resource in planning energy efficient renovations.
For more information, reach out to us at 4 Elements or check out the Canadian Association of Consulting Energy Advisors. And stay tuned for next month’s blog about airtightness — Part 2: Existing Homes.