If your home has a finished basement that was completed more than 10 years ago, chances are it wasn't insultated. So now it's costing you more than it should to heat.

Insulating could solve that problem, but if you use the usual techniques (insulating the basement from the inside) you'll create a whole bunch of new problems.

Examples: If your basement walls are paneled, you'll have to rip off the paneling, install insulation between the existing studs or furring strips, then reinstall the paneling (if it hasn't already been destroyed during removal). If your walls are covered with drywall, you'll have to go through essentially the same process, and then replace the drywall, retape it and repaint it.

One way around all these problems is to insulate the besement from the outside. This will let you leave the interior of the basement exactly as it is. You won't have to tear anything down, or put anything back up.

Insulating from the outside has other advantages, too. By putting the insulation outside, you turn your basement walls into a thermal "flywheel" that helps to stabilize the temperature in the basement, even when outside temperatures change. During the winter, the walls can hold a great deal of heat, releasing it slowly to the room whenever the air temperature starts to drop. In the summer, the exact opposite happens. The cool concrete walls soak up heat from the basement air, keeping you comfortably cool.

This type of temperature stabilization can't take place effectively if the indoor air is separated from the walls by a layer of insulation, as it would be if the insulation were installed inside the home. o

How do you go about insulating a basement from the outside? One common technique makes use of rigid tongue-and-groove foam plastic panels. The foam is fastened to the outside of your basement walls using either a special mastic suited for use with plastic foam, or with large-headed masonry nails.

The foamboard should cover the basement walls from their tops all the way down to the frostline in your locality. Covering the walls to the frostline will involve digging away the soil to a depth of three feet or more.

If that sounds like too much work, you can insulate from the siding to just a few inches below ground level. Then run a 24-inch-wide band of foamboard horizontally away from the wall, and cover it with a few inches of soil.

To prevent rainwater from running between the foam and the basement walls, you can install an inverted metal J-channel, caulked against the bttom edge of the siding.

Since plastic foam doesn't stand up well when exposed to the weather, some kind of protective covering is called for. One of the easiest to apply is a double coat of liquid latex cement. It goes on with a brush.

For specific instructions on this insulation technique, write to Dow Chemical, Styrofoam Brand Products, 2020 Dow Center, Midland, Michigan 48640. Ask for "How to Insulate the Outside of Your Basement, Crawl Space or Foundation Walls wit Styrofoam TG." QUESTIONS FROM READERS Q: I would like to build platform-type seating in my living room. I want it to look built-in, but for practically it should be free-standing and movable. I would also like to cover it in carpet and use separate seat cushions and throw pillows for the backrest.

What would be better for this, plywood and particle board? How should the unit be framed, and how can I attach a canted backrest to the seat platform? Also, are there standard measurements for the height and depth of such seating, and how can I best attach the carpeting? A: I'd suggest you cut out the bulkheads first, using 3/4" plywood or particle board and cover them with pieces of the same material, fastening everything together with white or yellow glue and 2" #10 screws.

Either particle board and plywood will do the job. Particle board will be about half the price of plywood, but is heavier and harder to handle and cut. Plywood will be stronger and lighter, an advantage if you want the unit to be movable.

The seat cushions should be about 3" thick. The carpeting can be attached with a mastic, or with carpet tacks, but you will have to do some stitching to join the edges together at the corners. It might be a good idea to have the carpet work done by a professional. Q: My wooden windows slide in metal frames and are very hard to move. What can I use to make them slide more easily? I have already tried wax, soap and furniture polish. None of these has solved the problem. A: You might try a silicone spray, but I'm not sure it will help. If it doesn't, you problem is more than a simple lack of lubrication. Either the windows are stuck to their tracks by accumulations of paint, or the tracks themselves have been painted, or the tracks are simply too tight.

Look for accumulations of paint first. If you find any that could be interering with smooth action, remove them with a stiff putty knife.

Most metal slides or tracks come either anodized or factory painted. They should not be painted by the homeowner. If yours are, the paint is probably causing the trouble. Try rubbing the tracks with steel wool. You may not have to remove all the paint. Just polishing it and wearing away may free things up.

If paint isn't the problem, suspect an overly tight fit between window and track. Most metal tracks have a lip that wraps around the window and provides enough friction to hold the sash in any position. Often this lip can grip the window too snugly. You can usually loosen it by slipping a thin putty knife between it and the window and prying. But sometimes there is a wooden molding called a window stop nailed up against this lip. If nailed too tightly against the strip it can create too much friction. To solve that problem you will have to remove the strip, then replace it with enough clearance to allow free action. An easy way to do this is to temporarily place a thin cardboard shim (matchbook covers work well) between the stop and the metal white nailing the stop back in place.