Before You Insulate

You Must Control Air Leakage

Most homeowners are aware that air leaks into their houses through what seem to be small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawl spaces.

The air travels through any openings in your walls, floors, or ceilings, such as cracks where two walls meet, where the wall meets the ceiling, or near interior door frames.

Other openings may also be found, such as gaps around electrical outlets and switch boxes, recessed fixtures, recessed cabinets, pull-down stairs, furred or false ceilings such as kitchen or bathroom soffits, behind bath tubs and shower stall units, floor cavities of finished attics adjacent to unconditioned attic spaces, and plumbing connections.

These leaks between the living space and other parts of the house are often much greater than the obvious leaks around windows and doors. Since many of these leakage paths are driven by the tendency for warm air to rise and cool air to fall, the attic is often the best place to stop them. It's important to stop these leaks before adding attic insulation because the insulation may hide them and make them less accessible.

Usually, the attic insulation itself will not stop these leaks and you won't save as much as you expect because of the air flowing through the insulation. Sometimes these leak locations are visible because the existing insulation has been stained by dust carried by the air flow. Some of the openings to look for include:

* Top openings of interior partition wall cavities: staple a plastic sheet over the opening and seal it around the edges with a high quality caulking material.

* Around the chimney: pack gaps around an insulated chimney with UNFACED rock wool or UNFACED fiber glass insulation. Do not insulate bare, hot flue pipes.

DO NOT USE ANY COMBUSTIBLE PRODUCTS, SUCH AS CELLULOSE INSULATION OR PLASTIC FOAMS, HERE.

* Around the attic trap door or entry door: weatherstrip the edges.

* Areas above staircase ceilings and dropped ceilings: staple a plastic sheet over the opening and seal it around the edges with a high quality caulking material.

* Around pipes (look under your sinks and behind your toilets) and ducts penetrating a wall or attic floor: pack insulation tightly into the gap. You can also fill the area around them with spray polyurethane foam.

Sometimes joints between walls and floors allow open passage of air between the heated part of the house and the attic area or outdoors. Look for such joints in your attic or in the space over a porch ceiling. This air leakage path is commonly found in Cape Cod-type houses, or if attic space has been converted to living space.

A similar arrangement occurs when the second floor of a two-story house is larger than the ground floor and has an overhang over the outdoors. Another major source of air leakage can be the joint between a porch roof and a side wall.

If you can reach these areas, you can stop the leaks by carefully covering the openings with plywood. If the areas are more difficult to reach, you can greatly reduce the air leakage by blowing high-density insulation or injecting plastic foam insulation into these joints, thus reducing these energy-gobbling air paths.

Back 11.11.2006.