Insulating the Attic over the garage

19 Sept 2009

Too wet outside to dig, so it's back to working in the attic.

I had an Energy Audit on 31 August. The audit was by Green Footprint Solutions who came in and tested the A/C ducts (less than 10% leakage), and a blower door test, as well as checking out the insulation of the windows, doors and in the attic. The audit pointed out that I had not quite finished the insulation and radiant barrier installation in the attic.

The missing insulation was mainly over the garage. Since the attic is uninsulated and the garage is uninsulated, it wasn't clear to me that it mattered, but the suggestion was that it would help cool the garage.
The supports for the garage ceiling are split into two halfs, left and right, by a beam running the length of the garage. I added 6 inches (R-19) in both the sections. This was John Mansville insulation from Lowe's. It slid inbetween the ceiling joists just about perfectly. I needed 3 packs, about 270 square feet.



This area is behind the knee walls that I installed previously. I was careful not to push it too far out, so that there is still ventilation from the soffits up to the ridge vent. There had been some plywood flooring tacked down that I had to remove to get it fully insulated.



If you look at the end of this section, where it abuts the attic area over the utility room, you can see that this is much less insulation than the rest of the house has.



So the next project will be putting up radiant barrier on the roof joists and then adding more insulation to really seal this area off. I have the materials. I had to buy more radiant barrier -- they don't make the kind that I used on the rest of the attic -- and I have R-30 batts to roll out over the new R-19 in this area. This
will bring this area up to R-49, better than the R-38 that is "standard" for this area. Most of the rest of the attic has another R-30 over this, which I guess would make it about R-80.



The R-19 (3 packs 87.18 square feet each) was $61.48 from Lowe's on 6 Sept 2009; the R-30 (9 rolls of 15 inch x 25 feet each) was $115.74 on 17 Sept 2009. The radiant barrier (2 rolls of 4 feet by 50 feet) was $95.99 on 19 Sept 2009.