March 10, 2020

The importance of an airtight home

From the perspective of a high performance builder

By: Ian Fung

So what’s all this talk about being airtight?  If you are in the construction industry right now, it’s the most talked about topic, with issues ranging from the blower door test to the materials and techniques used to address airtightness of a building.

So why is it so important now to have buildings airtight?  I would attribute the urgency due to the BC ENERGY STEP CODE standards being adopted by municipalities throughout the province that are causing builders to change the way they build.  But this topic of conversation can be endless and can branch off in all sorts of directions, see the diagram for only some of the benefits of having an airtight building.


I come from a construction background with 28 years experience in the field.  A few years back, I was managing a new home build in Vancouver BC which required a 3.5 Air Changes per Hour (3.5 ACH) maximum air leakage at final inspection.  This requirement was introduced into the Vancouver Building Bylaw as a means to make new homes more energy efficient and is tested and verified during the build process on two separate stages using a blower-door:

  • at Pre-Drywall inspection (meaning that all your insulation and /or poly is installed and the home is ready to begin drywalling)
  • at Final inspection (meaning the final inspection, where the home is finalized and ready for occupancy)

At first, this new requirement seemed like just ‘another annoying step’ added to the building and inspection process; I was always confident in the quality of my builds that I just shrugged it off.  That was of course until it was my turn to satisfy the airtightness requirement.  The Pre-Drywall test required a 5.0 ACH maximum, which I had satisfied, scoring a 4.9 ACH; I then proceeded to drywall and bring the home to completion.

It was on the final blower door test where all my momentum came to a crashing halt, I scored 4.5 ACH, overshooting the final requirement by 1.0ACH.  The Certified Energy Advisor (CEA), administrator of the blower door test, and I had identified several obvious leaky areas but it was ultimately up to me to find (and address) the rest of the leaks before he would return at a later date to perform another blower door test.

For the next six days, my worker and I went through every square inch of the house to search and seal off any possible air leaks; amongst the long list of techniques, we tried:

  • sealing the backsides of electrical boxes
  • sealing where wires poked through the poly boxes behind the low voltage mud rings
  • taping the areas where wires poked through the pot light poly enclosures
  • repairing poly we discovered as being cut in the attic areas
  • sealing around window trims
  • foaming around the holes of penetrations (inside and outside)
  • caulking the bottom plates in the crawlspace, where they were visible

Despite having gone through the home several times, from the basement right up through the attic and back again, I failed the blower door another three times.  It was on the fourth re-test that I managed to pass marginally with a 3.49 ACH; by that time, I was exhausted and completely drained and could not withstand another fail as we nearly disassembled the entire house twice over already.

This task of identifying and sealing leaks had cost me over $3600 in time and materials in addition to the $1000 for re-testing charges, totaling  $4600.  I could tell you a million other things that I would rather be doing and definitely would not wish that burden on anyone.  And honestly, how could one effectively seal the home once all the drywall and finishes have been installed?

So I re-evaluated my construction techniques and details for the next home and scored much better, achieving a final score of 2.50 ACH; at the time, I really considered this to be an outstanding achievement, until realizing what 2.5 ACH really meant:

2.50 ACH = 2.50 x the volume of air within the home that is exchanged under 50 Pascals of pressure

But still, what does that mean? 

A typical new home in Vancouver on a standard lot would be built to approximately 2800sqft and with 9’ ceilings, translating to a volume of 25,200cuft (2800sqft x 9ft).

At 2.50ACH, the home would exchange 2.50 times its volume: 2.50 x 25,200 = 63,000cuft

You are merely renting the heat rather than keeping it!

This is where one can relate to the term “throwing money out the window”; the money you as a homeowner would be paying to heat the air within the home is actually just being expelled outside at a rate of 2.5 times per hour!  Imagine that!  You are merely renting the heat rather than keeping it!  Of course the insulation of the home would play a large part in keeping the heat from escaping, but air leakage is the biggest and quickest transport of heat from the interior spaces to the outside.

air leakage

How much is this costing you throughout the year?  Don’t forget that air leakage also affects cooling just as much as heating; the cool air created from your AC is lost to the outside just as quickly in the summer time as the heat in the winter.

So how do we resolve this?  Make the home more airtight!  As I had described earlier with my experience in fighting air leakage, it is not easy, it takes an extremely dedicated builder to detail the home from ground up and he cannot do it alone, he must have his subtrades thinking the same.

At any rate, we are all humans and despite doing our best, there are other considerations which can limit the work that we propose to do, such as:

  • the weather
  • cost of the materials (specialty tapes, membranes, high performance windows and doors)
  • cost of labour
  • tiny holes throughout the house invisible to the human eye
  • human errors

Two years ago, I came across a technology which held the solution to addressing airtightness:  AeroBarrier

To quickly summarize what it does, basically it is a method of addressing air leakages in a building with the use of micron-sized sealant particles which finds its way to the leaks of the building and seals them when air pressure is applied.  This technology does not require the use of personnel within the building to identify the leaky areas nor does it require any personnel to physically seal the leaks; it is an automated, computer-driven process which yields precise real-time results, all performed within one workday.

Had this technology been made available to me back on that project, it would have been cheaper to apply this technology; furthermore, it would have saved me from all the guesswork and frustrations of addressing something which is basically invisible to the eye: an air leak.

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