by James Dulley
Engineering ConsultantReplacing a window with a door can make energy sense if done rightQ: In my dining room I have an old, wide window in a brick veneer wall. I’d like to replace it with a sliding glass door. Does this make energy sense? If so, how do I make this improvement?A: Your home improvement plan does make energy sense, but only if you select an efficient sliding glass door and install it properly. I made this improvement to my own kitchen last year.
The overall efficiency of an airtight sliding glass door can be better than an insulated partial wall with a large inefficient window above it. My double horizontal slider window had double-pane glass, but the gap seal failed on one panel and all the weather-stripping was worn out, creating air leaks.
Although homes are constructed differently, you’ll generally find a lot of reinforcing lumber framing around window openings. This is great for structural strength, but leads to inefficient thermal bridges and leaves little room for insulation. Once I removed the drywall, I found the sill plate had not been sealed properly and air was leaking in at the bottom of the wall. Seal as much of the sill as possible to the foundation.
I selected a super-high-efficiency sliding glass 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 high insulation level and cuts down on noise. Always select a door which is Energy Star® qualified and meets federal energy tax credit requirements.
Another option is double-swinging French patio doors. If you have clearance in your dining room for swinging doors, these are more efficient. Swinging doors close on compression weather-stripping, so they seal better over the long term than a seal on sliding glass doors. Also, when you open both swinging doors, there is more open area for natural ventilation.
Thermal Industries sent along an expert to help me with my installation. Here are some of the tips he taught me.
Spend a few extra dollars and rent a large masonry saw to cut through the brick wall in one pass from outdoors. I bought a cheap masonry blade for my circular saw. It cut through the brick, but I had to make both outdoor and indoor cuts to get through the full width of the wall. This led to an uneven cut and an unbelievable amount of dust indoors. Wear a good N95 breathing mask whenever you cut masonry.
With a brick veneer wall, the width of the brick and the total wall framing thickness will be about twice the width of the sliding glass door frame. The installer recommended positioning the door out on the brick to create a more stable door base. Indoors, this also recesses the door, making it easier to install tight thermal drapes during winter. The Warm Company makes good thermal drapes for this application.
For the simplest installation, cut straight down from the existing window opening. You will have to build out the interior opening with studs to the same width as the brick, but this is still easier than resizing the entire opening. This will leave a 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 and expands, the insulation 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 for all screws and don’t over tighten them. The framing on a large door can easily be pulled out of balance during installation without supportive shims.
My door frame was placed over pressure-treated lumber trimmed with aluminum flashing to raise it because I mistakenly cut the brick too low. Whether you’re installing a door over lumber, brick, or a precast sill, liberally apply silicone caulk between the bottom of the door frame and the base to prevent leaks. There are weep vents in the door track to prevent water collection.
To see all the project photos and details, visit www.dulley.com/newdoor.James Dulley is a nationally syndicated engineering consultant based in Cincinnati.
If you have a question about energy use or energy-efficient products, send it to: James Dulley, Electric Consumer, 6906 Royalgreen Drive, Cincinnati, OH 45244; or visit www.dulley.com.