I've been reinsulating some spaces around our house that the very cold winters of recent years have shown are not as tight as they should be.

One thing I've been doing - thanks to helpful advice over the years from Hap Haven, the Germantown-based energy expert - is taking this important preliminary step:

Closing any gaps before insulating.

Use foams and sealants to eliminate any penetration to the outside, such as at the ends of joists at the front and back of the house.

Sealing the gaps - you can tuck white or black plastic bags into the cracks (clear ones decompose) - prevents heat from escaping and moisture from entering the attic, for example, without interfering with the required ventilation.

With that done, you can go ahead and insulate.

The basement is another place where air sealing will reduce heat loss and moisture intrusion by reducing incoming air flow.

I have been using foam to seal the space where our front porch meets the foundation of the house, because the cold air from that space finds its way into the front walls of the room we refer to as the library (because the television is there, it is the place once known as a "den"), as well as our living room (which has a fireplace and the piano but is otherwise unused).

Basement windows tend to be the worst cared-for in a house, so you want to be sure too much air isn't escaping through them. I have new windows, but I use weather stripping to tighten them up a bit.

Still, you can't make a basement too tight, Haven said.

"The basement is the source of replacement air," he said, especially in houses in which stud-wall cavities run from basement to roof.

"It is better to seal spaces that run from the basement along interior walls and out, such as utility chases and other openings, so that the heat doesn't escape."

When you work with foam insulation, or insulation of any sort, for that matter, wear a mask, gloves, a hat, and loose-fitting clothing.

Foam insulation in your hair is worse than bubble gum, by a long shot.

aheavens@phillynews.com or write him at The Inquirer, Box 8263, Philadelphia 19101. Volume prohibits individual replies.