One of the strongest recommendations from the energy audit guy was to properly seal the underside of the overhang to stop drafts. The floor at the front of the house on the bedroom level overhangs by about a foot. He recommended removing the plywood that covered the underneath to expose the joists, then add some rigid styrofoam that was properly caulked to seal the drafts and add a bit of insulation. Since there was an incredible draft coming into the basement from that area, I really wanted to do that. This is their story. (Apologies to Law & Order.)
This is the underside of the overhang after the plywood was removed. The black stuff there is called Black Joe - it is like pressed fiberboard (made from wood pulp) that is impregnated with some sort of black stuff, tar or something. If I installed the rigid insulation on top of the Black Joe, then the effectiveness of sealing against drafts would be dependent on how the Black Joe was sealed. Due to the age of the house, it was pretty clear that this was extremely unlikely.
This is what I saw after removing the Black Joe. You can see that the insulation doesn't extend all the way to the end of the joist space. Obviously I needed to add insulation before I put the rigid stuff up.
What a surprise! There was absolutely no insulation in the area under the front coat closet. You can see why that is in this photo - there is a piece of blocking across the joist space (at the back left of this photo). Not sure why the blocking was there as it totally prevented anyone from putting insulation in this area.
This photo shows the empty joist cavity was filled with insulation (Roxul). That's the equivalent of R-28 in this cavity now.
This photo shows the joist cavities were filled with Roxul (R-14 per layer, so it is R-28 for the two layers). Then a 1" thick piece of rigid styrofoam was added, on top of a bead of acoustic sealant - that's the black squiggly line on the rim joist at the left.
After the 1" piece was put in, another 1/2" thick piece was added. These two layers fitted above the top row of bricks. This photo shows the two layers of rigid styrofoam.
Looking down the side of the house. You can see it was so nice that we were wearing just t-shirts. Of course, it was a bit chilly if you were in the shade.
We added another 1/2" thick piece of rigid styrofoam under this, for a total of R-10 for the foam, so the total insulation added is R-38.
I had to rip the plywood narrower because (a) the edge got a bit chewed up when it was removed, and (b) the plywood could no longer fit on top of the brick because that space is now filled with styroam. This photo was taken after the plywood was installed - with screws, because it would compress the layers of foam together, helping eliminate any paths for air to take.
Oh, I had exactly enough Roxul to finish this! I only had a little piece about 4" x 5" left. Zowie!