Important dos and don'ts of insulating walls

It's easy to insulate your walls with fibreglass insulation. But the job still requires attention to detail to get the maximum benefit since every gap and compressed batt could let heat or cold escape. Here are a few important dos and don'ts to help you get the job done right.

• Add about 0.5 centimetres (1/4 inch) to your measurement to ensure a snug fit.
• Use a 10 to 15 centimetre (4 to 6 inch) wide board or strip of plywood as a straightedge to guide your utility knife.
• Line up the edge of the board at the proper width, compress the insulation and cut it with a sharp utility knife.
• If you put a scrap of plywood under the batt, you can protect finished floors and keep your knife's blade from dulling on concrete.

• Crumpling batts to fit narrow spaces creates uninsulated air pockets.
• And packed insulation has a lower R-value (the standard measure of thermal resistance).

• Paper facing makes cutting the batts difficult.
• And it's hard to create a tight vapour barrier with paper-faced batts.

• Put the batt in place, and use scissors to snip around the box.
• Tuck the snipped-out plug of insulation behind the box.
• Don't wrap fibreglass batts around electrical boxes or stuff full batts behind them.
• Doing so creates gaps and air convection routes around the box.

• Do split apart the batts to fit them around wires and pipes.
• Doing this will help you get the full value out of your insulation.

• Compressing full-thickness fibreglass batts decreases their insulating value and creates voids between the insulation and the drywall.

• Do plug holes in the top and bottom plates with expanding spray foam.
• Even small holes can let a lot of air escape.
• Don't leave gaps around wires, pipes or ducts unplugged.
• These gaps create pathways for warm interior air to leak into the attic, wasting energy and causing attic condensation or even ice dams in cold climates.

• Do buy unfaced friction-fit batts and seal the walls with a 4 millimetre (1/6 inch) poly vapour retarder.
• Seal the gap between the bottom plate of the wall and the floor with acoustical sealant or caulk.
• Press the poly into the sealant.
• Use special airtight electrical boxes or seal the poly to your electrical box(es) with acoustical sealant.
• Tape any seams you have in the poly with sheathing tape.

• When you're working with fibreglass, you should wear safety goggles and a dust mask.
• If you're installing a lot of fibreglass, consider wearing a disposable coverall (found at paint stores and home centres).

• Seal around window and door jambs with expanding spray foam.
• The main purpose of the spray foam is to seal the space around the window to prevent air infiltration.
• Use foam that's labelled for window and door insulating.
• This "minimal-expanding" type of foam reduces the chance of warping the door or window jamb.
• If there's still space around a window after the foam cures, lightly stuff the remaining space with strips of fibreglass insulation.

Keep these important dos and don'ts in mind to help make insulating your walls easier.