Seal Cracks Between Boards for a Tighter, Healthier House

My husband and I purchased a Bungalow-style house built around 1920. When we removed the old ceiling tiles we found tongue-and-groove boards, but the years have left gaps of up to a half-inch between them. The boards also are visible from the attic. How do we seal up the gaps so insulation, dust and bugs don't drop into the living areas? We want to add recessed lights in the ceiling and insulation in the attic.

As charming as old houses can be, they do present some challenges. Preserving the authenticity of your T&G ceiling will be more work than covering it up with drywall or tearing it out and starting over with new lumber. But the house wouldn't be the same.

Making those cracks all but disappear

There's not much you can do about the gaps that have opened up between boards in the ceiling. But you may be able to disguise them. Gaps as wide as a half-inch may indeed allow attic insulation and dust to drift into the living areas of your home. Caulk probably isn't your solution. It's not made to span gaps that wide, it doesn't bond well to dusty surfaces and it can shrink over time.

One possible fix is to rip pieces of quarter-inch plywood into strips, paint them flat black and fit them between the joists in the attic.

This isn't a perfect solution but it should make the spaces between boards less obtrusive. Try a test piece. If black doesn't work you might tinker with a color that more closely matches the color of the boards in the ceiling.

Block air leaks into the attic

Before you insulate, you'll need to create an effective air barrier between the house (the "conditioned space") and the attic. In extremely cold climates, you would add a polyethylene vapor barrier on the warm side of the ceiling -- that is, right over the ceiling boards -- before installing attic insulation. That would serve as both an air and vapor barrier.

But an impermeable barrier like polyethylene can cause problems, too, especially if you run air conditioning in the summer. If you can block up any and all air leaks, the amount of moisture getting into the attic will be minor. So that's where I'd put my efforts.

Go through the attic thoroughly and identify any opening that might allow warm air to escape from the house. Look for gaps between the chimney and framing and for plumbing and electrical chases. Check for gaps around ventilation fans.

Seal all these leaks with expanding polyurethane foam. For very wide gaps and holes, use pieces of rigid foam insulation and seal them in place with foam. Around the chimney, use a non-combustible material.

Be careful with recessed lights

If you install recessed lights (cans) in the ceiling, make sure they are IC rated, meaning they are designed to come into contact with insulation. Newer designs are airtight, which is even better.

If you have old style cans, insulation must be kept at least 3 inches away from the light housing. You'll have to build a "hat" for each fixture. You can use 1-inch thick duct board faced with foil and allow plenty of room between the board and the light.

Now add insulation

With all of this out of the way, you're ready for insulation. Blown-in cellulose or fiberglass will make your house a lot more comfortable and save you money. Just make sure to follow local energy codes by adding a sufficient amount (you can check at www.energystar.gov).

Insulation and air sealing is complicated. If you want to do more background reading, try the web site for the government's Energy Efficiency and Renewable Energy office (www.eere.energy.gov/consumer) or a book by Bruce Harley called Insulate and Weatherize from The Taunton Press.