I have to admit, building an airtight house, it is MUCH more difficult than I thought.  I previously mentioned that my wife had taken to calling me Mr. Foam.  It is a good name for me; I spent a great deal of time and effort making sure to seal every gap I could find. 

I spent a few hundred dollars for cans of sealant foam, and for months, I was Mr. Foam.  I had foam on my skin, and in my hair.  I had foam on my clothes and on my shoes.  When my boys tried to determine what daddy had just foamed, they inevitably ended up with the sticky foam on their skin and clothes as well.  For months, foam was my friend.  Naturally, when blower door test time came, I was prepared to be the tightest house built in the region.  Unfortunately (and disappointingly) this just didn’t turn out the way I expected.

Our ACH @ 50 pascals was 1.18.  This translates to 0.09 natural air changes per hour.

While certainly a “tight” house by any standard, it is by no means a record of any kind.  During the test I was able to locate, but not eliminate, the sources of some of the leakage.  A large amount of air was coming in from the area behind the upstairs blower unit, ductwork, and ERV.  It was difficult to reach and the spray foam contractor missed part of it.  They came back quite honorably, and without giving me any hassle, I might add.  They used a different type of (injectable) foam to reach the area that could not be sprayed directly.  Unfortunately, when this new foam dried, it contracted and lost some of its effectiveness.  I’ve sprayed several cans of expanding foam into this same area and I still don’t think it is sealed to the standards of the remainder of the house.

There were other leaks as well…  I found an open 4” drain under the floor in the attic and a floor drain in the basement.  Even with my air sealing efforts I was still able to find small holes in the insulation.  I can only hope that I got them all after the blower door test.

My advice to anyone – especially those of you using a general contractor for the entire project – do a blower door test. 

Uncontrolled air infiltration adds substantially (much more than most people know) to your heating and cooling loads.  Think of it this way… you spend all this money for insulation.  (In our case, our outside walls are R47.)  Any place where uncontrolled air comes into the house, insulation is defeated – it’s R0.  In addition to adding to heating and cooling loads, uncontrolled air flow through the building envelope can cause moisture issues in the walls.  If you can, get your contractor to agree to the blower door performance.  Get your desired value in writing!  This way he will be responsible for sealing any holes in the building envelope.

Good luck,
Ed