Proper sliding glass door can be more efficient than partial wall
Q. I have an old wide window in my dining room (brick veneer wall). I want to replace it with a sliding-glass door. Does this project make energy sense and, if so, how do I make this improvement?
A. Your plan does make energy sense if you select the proper sliding glass door and install it properly. In fact, I just made the identical improvement to my kitchen several weeks ago. The overall efficiency of an airtight sliding glass door can be better than an insulated partial wall with a large inefficient window above it.
I selected a super-high-efficiency Legance door made by Thermal Industries (www.thermalindustries.com). It uses a steel-reinforced vinyl frame and triple-pane glass panels. Two of the glass panes have a low-emissivity coating and dense krypton inert gas between them. This provides a very high insulation level and less noise transmission. It is Energy Star qualified and meets the federal energy tax credit requirements.
Thermal Industries sent along one of their installation experts, Paul Robinson, to be a helper for me as they do for many installations. After talking a bit, I realized he knew much more than I and I became the helper. I will pass along some of the installation tips Paul taught me.
Spend a few dollars extra and rent a large masonry saw to cut through the brick in one pass. I bought just a cheap masonry blade for my circular saw. It cut through the brick fine, but I had to make both outdoor and indoor cuts to get through the full width of the bricks. This resulted in an uneven cut and unbelievable dust indoors. Wear a good N95 breathing mask.
The width of the brick and the wall framing will be about twice the width of the sliding glass door frame. Paul recommended positioning it out on the brick. This creates a stable base. This also recesses the door in the opening so it is easier to install tight thermal drapes during winter.
The width of the exterior brick opening will be less than the interior rough wall stud opening. Build out the interior opening with studs to the same width as the brick. This will leave an uninsulated gap between the new studs and the brick which must be insulated.
I used Great Stuff low-expansion foam, but fiberglass is also effective. Once the foam is sprayed in, this was covered with 3/4-inch pressure treated plywood. Thermal Industries had custom-sized the door to fit in this final opening size with about one-half inch overall clearance. Make sure to use shims at all the screws and don't overtighten them. The vinyl frame can easily be pulled out of square during installation.
My door frame was placed over pressure-treated lumber trimmed with aluminum flashing to raise it because I had cut the brick too low. Whether being installed over lumber, brick or a precast sill, liberally apply silicone caulk between the bottom of the door frame and the base to prevent leaks.
To see all the project photos and details, visit dulley.com/newdoor.
Q. I was approached by a local company that installs insulation. They said I should install another layer in my attic. There already are about 6 inches up there. How do I know when I have enough insulation?
A. Additional insulation always helps, but the actual amount of savings per inch decreases with each additional inch thickness. At a point, the cost of installing the insulation exceeds its payback potential.
Talk with your local building inspectors or utility company to find out the recommended amount (R-value, not thickness) of attic insulation for your area. As long as you have this much, the payback from installing more would not be worthwhile.
• Write to James Dulley at 6906 Royalgreen Drive, Cincinnati, OH 45244, or visit dulley.com.