Step 22 – Air Sealing & Insulation

After passing the HVAC and rough framing inspection, I now had permission to enclose the walls of the house. The first step was to ensure that I had minimal air leakage through the wall. Air in motion is quite efficient at transferring heat and moisture, both of which I want to have tight controls on, so it is very important to ensure air can’t move through the walls of the house. I laid down a bead of spray foam around the perimeter of every stud bay, and also inside any holes where wires or plumbing penetrated the perimeter of the stud bay.

I also applied caulk to any openings in the electrical gang boxes. You may not think about it when you look at them, but every single outlet and light switch in your house is a potential spot for air to move heat out of a room, or move dangerous moisture inside a wall assembly. Every place the wires exit those switches and receptacles must be air sealed with caulking.

The lower 16 inches of the attic must be air sealed as well, since this is the part of the attic that will contain the insulation. Loose fill cellulose insulation like the kind I will be using to insulate the attic performs by trapping air, so it will perform much more efficiently if I ensure there is minimal air movement through it.

The joist bay between the first and second stories of the house must also be air sealed. I insulated this area at the same time as I air sealed it because it would be very difficult to properly insulate it with the dense packed cellulose. I had some extra polyisocyanurate foam from cutting out holes for the windows and doors, so I cut it up into pieces that fit inside the joist bays and foamed around the edges. Then I repeated the process so there were now two layers of foam.

Doors also have potential for air leakage. I inspected all the doors for a nice tight seal between the door and the weather stripping. On one door I needed to add some paper shims behind the hinges to push the door towards the opposite jamb so there wasn’t as much of a gap between the door and the jamb. This moved the door into better contact with the weatherstripping. For the corners of the doors, you can buy small foam pieces that help cover tiny holes between the door and the corners of the jambs.

4 Comments on “Step 22 – Air Sealing & Insulation

  1. Love seeing those electrical gang boxes caulked .Haha I’ve never seen that be done before but I suppose if air sealing is the goal then you are definitely hitting it.

    • Air sealing is important bro. Not only are you reducing heat loss through convection but you are also ensuring that all of the air you breathe has been run through a HEPA air filter. Most importantly, moisture is carried through the air as well and being the most damaging thing to a house, you want to control moisture in every way possible. Here is a good article on air movement through outlets. I should be doing my blower door test this coming weekend! Come on down if you have time.

  2. A pet peeve of mine. Why don’t they design doors with integral weatherstripping so they don’t need those small pieces of foam etc… to seal air tight. ( as they should!)

Advice? Questions? I'd love to hear your feedback or help you out in any way I can!