Time is running out! We’ve been discussing tips on making your home more energy efficient so that when winter rolls around you’ll be warm and snuggly on our couch without astronomically high utility bills. Part 1 identified common locations of air leaks, Part 2 discussed preparing and gathering materials, and Part 3 got you going in the attic. Have you started yet? Good.
Wait! Don’t take a nap yet! Let’s move on to the next phase.
Seal behind the Kneewalls
If you have a finished attic, then it is likely there are open cavities in the floor framing under the kneewalls. (Kneewalls are the short side walls that drop from the sloped ceiling down to the floor.) Even though insulation may be piled against these spaces they can still leak air. You should plug these cavities in order to stop air from escaping from under the floor of the finished attic.
To do so, cut a 2-foot long piece of fiberglass insulation and put in a 13-gallon plastic garbage bag. Fold the bag over so the batt is folded over on itself and then stuff it into the open joist spaces under the wall. If you’re using rigid foam board instead of batt fiberglass insulation, then cut a piece to fit snuggly in the joist opening, and use spray foam to seal the edges and hold it in place. When you’re done, push the existing insulation back in place.
Seal around Furnace Flues
Gaps around a furnace or water heater flue or chimney can be a major source of warm air leaving your house and moving into the attic. Since the flue pipe gets hot, building codes usually require a minimum clearance to any combustible material, and that includes insulation. The clearance is usually a 1-inch space from metal flues, and a 2-inch space from masonry chimneys, but be sure to check your local building codes to be sure. And BEWARE! They may be very hot right now, so be careful working around them!
How can you keep this required space, but still seal air leaks? For round metal flues, cut out half-circle shapes in two pieces of aluminum flashing so they fit tightly against the flue and overlap each other a few inches on either side. Put a bead of high-temperature caulk on the surface that the flue passes through and press the flashing onto it. If the surface is wood, then and staple or nail the flashing into place. If the flue passes directly through drywall, or some other thin finish material, then staple or nail it directly into that if possible, but be sure not to go all the way through. Then seal the small gap between the flue and metal flashing with special high-temperature caulk. This is NOT a place to use spray foam!
The next step is to build a metal dam to keep insulation from touching the flue pipe. Cut a piece of aluminum flashing that is high enough to stick at least 1-foot above the level of the insulation, and long enough to wrap around the flue plus 6 to 8 inches. This piece should fit around the flue but with the required one inch gap. Then make tabs by cutting 1 inch deep into the top edge every inch and bend the tabs in toward the flue. That holds the dam 1 inch away from the flue. Next make tabs on the bottom edge by cutting 2 inches deep every inch and bend the tabs out away from the flue. Use this to anchor the dam to the surface that the flue passes through. Wrap the dam around the flue and secure the bottom by stapling through the tabs. Now you can put the insulation right back up against the dam.
Have a masonry chimney? Use the same method above, but adapt it to the square or irregular shape of the masonry.
We’re making progress! But stay tuned for the next installment from GAMA Air about sealing the small, hidden gaps that can also be a big energy loss. UPDATE:Read Part 5 here!
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