MIKE DiGREGORIO, Wilmington

A. OSB (oriented strand board) is good for sheathing, far better than particleboard, which, in my opinion, should not be used for sheathing anywhere. OSB has a rating very close to plywood of the same thickness, and has been used successfully in prefab houses. Use one-half inch for walls, and five-eighths inch for roofs. For floors, I suggest using plywood, whether you put down one layer or two.

Q. I plan to remove the insulation between the rafters in my attic and put insulation in the attic floor. There are floorboards in the attic; I plan to blow in granulated insulation under the floorboards. Will that work?

DAVID JERISON, Belmont

A. Taking the insulation from between the rafters (the sloping beams holding up the roof) is a good idea because it is doing little good there; heat is being lost through the floor and is being stored in the attic; in other words you are heating the attic for no good purpose. And that goes doubly if the attic is ventilated.

Blowing insulation under the floorboards is good, but be sure that no insulation gets into the eaves (the underpart of the roof overhang). Insulation in the eaves could cause condensation of water vapor into water, a serious problem in an attic. It also could cover any soffit vents (the soffit being the horizontal underside of the eave), and that is not good.

To prevent this, install baffles at the ends of the joists where they form the eaves. Better yet, bite the bullet, pick up the floorboards (no easy task, admittedly), and install fiberglass batts, or rolls, with the paper backing (a vapor barrier) against the ceiling below. The vapor barrier is important in keeping heat in the house where it belongs. Insulation by itself, while important, is not enough.

Then put the floorboards back. Sure it's a lot of work, but the job will be done right.

Q. I have so much insulation on my attic floor that some of it comes right up to my waist. Is that overkill? I'd like to put some floor boards on the floor for storage.

J.M., Reading

A. You cannot overinsulate, especially on an attic floor, but there is such a thing as a point of diminishing returns. In other words, adding a foot of insulation to 3 feet already there will do very little extra good. And extra thick insulation does more harm than good if it blocks soffit vents or goes into the soffit, which can cause major condensation problems.

So, 18 inches of fiberglass, with an R value of 57, is optimal. But that still does not allow you to put floor boards down. So you can do this: Take out some of that insulation where you want to put the floor boards, then nail 2-by-6s at right angles to the existing joists. Fill the space between the new joists with insulation, then put the boards on. This will provide 12 inches (R-58) under those boards, which is more than adequate.

Q. I have a plague of dust kittens in my bedroom. I had some work done on the house, including insulating water pipes in the attic above the bedroom with fiberglass batts wrapped around the pipes. Also, there were fiberglass blankets put over the pipes. Is this insulation causing the dust kittens?

E.S., Peabody

A. I don't think those kittens are fiberglass, which is usually yellow or pink, although there is some white stuff out there. The fiberglass in the batts, wrapping the pipes, is quite secure, and it would take a lot of abuse (rubbing, abrading and otherwise fiddling with the material) to release any fibers.

Besides, even if the fiberglass were loosened, it is unlikely that any would find its way through the ceiling and into the bedroom. The same goes for the fiberglass blankets, which will remain in position as long as they are not disturbed, and they are not likely to be disturbed in an unoccupied attic.

The kittens might be cellulose insulation, dropping from holes in the ceiling, but if you have no holes, or the holes are sealed, then the cellulose (most likely, if at all, on the attic floor) will stay where it belongs.

I think they are, indeed, dust kittens or dust bunnies, and the only thing you can do is sweep or vacuum them up.

Q. My 70-year-old house has insulation in the attic floor and also in the roof, the ceiling of the attic. I was told that such insulation in the roof could cause decay. It has been up for five years, and I have found no moisture in or behind the insulation. There are no vents in the attic. Must I vent the house?

JOHN WASHEK, Dedham

A. You don't have to vent inside the house, unless you have a lot of moisture condensing on windows, walls, and ceilings. While insulation in the roof (the attic ceiling) is generally not recommended in Northern climates, if it continues to be dry, be thankful that it is dry. Insulation in the attic ceiling will not do much in winter, but in summer it could keep the attic a lot cooler. This is especially so in the long hot summers of the South. Without moisture, you will get no decay.

Normally insulation in the attic ceiling, between rafters, is installed with an air space between insulation and roof boards. This space is also ventilated, with soffit vents (under the eaves or roof overhang) at the bottom and a ridge vent at the top.

If you vent the attic, the insulation would be doing even less good, although I repeat that in summer it will work to keep the attic cooler. It would not hurt to vent the attic; this is best done with soffit and ridge vents, as suggested above or, less effective, with large louvers at each gable end of the house. Whatever you do, inspect that insulation for moisture twice a year. You never know when moisture shows up. And when moisture comes, can decay be far behind?

Q. I have a laundry on the second floor of a new Cape-style house, with the trap of the washer drain in the crawl space behind a low knee wall. It was insulated against the cold of the crawl space, but not enough, because the trap froze. The contractor returned to reinsulate the trap and drain, and wrapped polyethylene over the new insulation. Will this poly be a problem? Will it cause condensation?

ROBERT CARON, Rye, N.H.

A. No. There's not enough air in the space behind the poly to create a problem. But be sure there is enough insulation on the trap and the drain, although it is most important to insulate the trap, because it holds water, while the drain does not have any water in it except when the washer is emptying.

If the present insulation is not enough, the best way to insulate it is to build a box around it and stuff it with insulation, making sure there are no air leaks through the box.

Ah, those stopped-up dishwashers, and the problem one reader had. The handyman suggested it might be a kinked or blocked hose. Fran Hintsa of Newton called to tell us she had the same problem, but a different cure. ``I wasn't running the dipsosal when I drained the dishwasher. It drained when I ran the dipsosal. Also, the strainers can get clogged. The strainers are under the wand at the bottom of the dishwasher, and they can be cleaned.''

It sounds weird that the dishwasher won't drain when the disposal is not on, but I suppose weird things happen. It sounds as if the dishwasher drain goes through the disposal, which is interfering with the drainage. Have a plumber check it, because there is no reason that I know for such an arrangement.

Q. I replaced my wood double-hung weight-balanced windows with vinyl windows, and I like them very much, but I fired my carpenter because he did not fill the weight pockets with insulation. I still want to fill those weight pockets, which lose a lot of heat in winter. One man suggested spraying in a foam sealant, but another said the foam expands too much and could distort the window frames. A third man suggested drilling two holes in the weight pocket and blowing in insulation. What is the best way to go?

PAULINA ROBINSON, Chestnut Hill

A. One of the main points of replacing windows (just the movable sash, not the whole window and frame) is to fill the weight pocket with insulation. If that is not done, the replacement window is no different from the old window plus a storm.

While blowing in foam is an excellent way to insulate that pocket, because it fills every nook and cranny, it can over-expand if the installation is not just right. Therefore, I would go with blowing in standard insulation such as cellulose or fiberglass.

Q. I plan to rebuild the 2 x 4 walls in my basement, but do not plan to put in insulation. A man at the store suggested putting up a vapor barrier on the inside of the studs (facing the room). Would that be a good idea without insulation? I also am not very good at toenailing the vertical studs into the base plate and the top plate. Any shortcuts?

E.H., Hudson

A. If you keep the walls uninsulated, I would not suggest putting in any vapor barrier; moisture could get caught behind it and condense, not a good situation. I think it's best to fill the space with insulation; then you can put on the vapor barrier.

As for toenailing (driving nails at an angle through the studs and into the floor or top plate), there are shortcuts. First, drill angled holes in the stud to ease the hammering. Then cut a 2 x 4 15 1/2 inches long and set it on the floor plate. Butt the first stud against it; it will act as a block to keep the stud from moving when you whack it. You have to step on the block for the first stud. For succeeding studs, the block also acts as a spacer, making it easy to space the studs 16 inches on center.

Q. Will mildew make fiberglass insulation less effective? Some of my insulation got wet, and mildew grew.

J.B., Marblehead

A. Mildew will not reduce the effectiveness of fiberglass. Even dampness will not affect the fiberglass' ability to insulate. After the fiberglass dries out (and that may be a while inside a wall cavity), the mildew will go dormant, but is still likely to smell funny. Of course, if the insulation sags and collapses inside the wall, it is useless.

Q. My house is only eight years old, and I am getting a lot of cold breezes into it -- through wall outlets and especially around recessed light fixtures in the ceiling between the beams. The ceiling is sloped.

D.B., Hingham

A. Even in new construction, insulation can get left out, but that probably is not the case with your house. As for the breezes through the outlets, it may be a matter of sloppy installation of insulation around them. You can check this way: Turn off the power first, then remove the outlet plate and pull out the outlets as far as possible (they are hooked onto wires, of course) and check behind the box to see the condition and location of any insulation. It may be difficult to rearrange the insulation so that it covers the box and opening, but that is what should be done. If there is much of a space between the edge of the box and the opening in the wall, you can caulk it. Do not use caulk inside the box. Another partial cure is to cover the outlets with foam covers. If push comes to shove, you can cover the box and opening with a foam cover; this will stick out beyond the outlet plate, which may look weird, but it will stop the breezes. If that works, you can devise an extra large outlet cover.

As for the recessed light fixtures, they may be the old-fashioned type that cannot be covered with insulation because of the danger of heat buildup; in fact, insulation should be kept 2 inches away from them, with no insulation over the top. Checking will determine this. If they are the old-fashioned type, replace them with the no-clearance fixtures, which will allow insulation to be put over and around them. Such fixtures are labeled ``no clearance.''

Q. I plan to Sheetrock the outside walls of a closet in the basement. There is a vapor barrier on the other side of the wall, behind the inside cedar lining, but there is also one on the outside of the wall, next to the insulation. Should I remove that vapor barrier?

JOE MARTIN, Centerville

A. The rule with insulation and vapor barriers is that you should have only one vapor barrier; with two you could trap moisture in the wall, which would be bad. So, the best bet is to take that extra vapor barrier off.

Q. I must be losing heat someplace in my house bcause I get a a lot of icicles on the edges of the roof. I have 6 inches of insulation under the attic floor boards, and 6 inches on top of the boards. Shouldn't that be enough? There is plenty of snow on the roof, and it stays quite a while.

STEVE AZARIAN, Albany, N.Y.

A. It's enough, but it might be in the wrong place. If there is a gap between the insulation under the boards and the boards themselves, then the insulation on top is doing very little, because cold air gets between the two layers of insulation. And, if you have soffit vents (vents in the underpart of the roof overhang), you may be getting even colder air into that space. To correct this, remove the floor boards and put that top insulation directly on the lower insulation. If you need a floor, you could install 2 x 6 joists at right angles to the existing joists and put the floor on those joists. Finally, make sure the soffit vents allow air to come into the attic.

The fact that you have icicles doesn't always mean that you are losing heat; the snow on the roof indicates that you are not. Icicles can occur any time snow melts, and that snow might be melting from the top down, the way it is supposed to. And, if you don't have any leaks, you should be OK, even without relocating the insulation. The only hazard the icicles cause is falling on someone. So, knock them down when they get big enough to be a hazard.

Q. My storm windows are steamy on the inside, and when that ``steam'' turns to ice I'm in big trouble. I thought everything was tight, but something is fishy. What is it, and how can I fix it? I'm 90 years old, so don't make it too difficult. Most of the affected windows are on the second floor.

MARIE LOCKE, Lexington

A. The handyman is impressed by a 90-year-old who does a lot of things around the house. Maybe they keep you young.

The fix is relatively simple. In fact, this answer is also for Angela, who called with the same problem.

The cause: But before fixing it, let's get to the bottom of such condensation, why it happens and where.

We manufacture water vapor in our houses by breathing, cooking, washing, and bathing. This water vapor builds up in the house because it can't escape to the outdoors (usually in tight houses). Finally it saturates the air and condenses into ``steam'' when it hits a cool surface.

The water vapor condenses on the inside of the storms because the inside windows are loose. This plague occurs on second-floor windows more than first-floor windows because warm, humid air rises.

The cure: So, weatherstrip the inside windows, whether they are new or old, because new windows can leak air, too, although they are not supposed to. Sometimes the water vapor doesn't go through the window or even around the edges, but rather sneaks around the casing, the wood frame around the window. In that case, you can caulk the edges of the casing. It might not look so hot, but usually windows are covered by curtains or draperies, so it should be OK.

The easiest way to weatherstrip windows is with Mortite, a flexible rope type caulking. Press it into all edges of the window: sides, top of the top sash and bottom of the bottom sash, and particularly at the check rail, where the two sashes meet. Of course, you have to pull this stuff off in the spring when you want to open the windows. The Mortite claims to be re-usable, but often it gets too hard to re-use. But it is inexpensive.

You can apply a weatherstripping such as spring bronze or a vinyl bulb-type stripping for a permanent fix. It is more work to install and more expensive, but it is at least as permanent as windows seem to be these days.

One more little thing. The storm windows normally have small weep holes at the bottom of the outside aluminum frame, one about four inches in from each side. These serve two purposes: 1. To allow moisture to escape. 2. To allow any water that gets between the storm and inside window (usually happens in the summer, when the screens are up) to drain.

Without this drainage, the water sits there and can rot a wood sill in a matter of months. Make sure the storms have those weep holes and make sure they are open. In fact, you can drill 1/8-inch holes at the top of the frame to allow faster escape of the water vapor. (Remember, moist air rises. The weep holes, plus any extra ones you drill, will not affect the insulating quality of the storms.

Also, at a change of season (from warm to cold weather), we have to contend with excess moisture in the house built up during the summer, and it takes time for it to dissipate, usually by heat. The steaming might be less (and tolerable) by Christmas.

Finally, if the condensation is really excessive, you can open both storm and inside windows to allow it to escape. Just a few mintues a day will help.

If all these fixes don't work, you'll have to live with the condensation. The handyman has minor condensation on his windows (on the second floor), which he is able to live with.

If you are able to reduce the water vapor, that's great, except by the time the water vapor is reduced enough to eliminate the ``steam,'' the house is too darned dry.

Another plague (In fact, the handyman received questions on this subject just last week): ``steam'' on the inside of the inside windows, including old ones and brand new insulated (double glazed) ones.

The cause: Excessive water vapor in the house, condensing on the cool glass, and the glass of insulated windows can be cool enough to cause condensation.

The cure: Reduce the water vapor in the house by opening windows twice a day for 5 or 10 minutes. You will not lose much heat at all, but you will reduce the water vapor, perhaps enough to eliminate or reduce the ``steam'' to tolerable levels.

Q. I am considering insulating my basement ceiling. The basement is not lived in. Will insulating the ceiling make the basement too cold? And will it really save heat? What insulation is best put in the ceiling, and how can I install it so it doesn't fall down?

JOE JOYCE, Arlington

A. Some good questions you have there, but all answerable. Insulating the basement ceiling will not make the basement too cold; an unheated basement will rarely get below 40 degrees even in extreme cold. One thing to guard aginst is freezing of water pipes that are within a foot or so of the foundation. The handyman's basement ceiling is insulated (of course), so every fall to protect against freezing of pipes (it has happened in the past) he hangs a 75- or 100-watt trouble light over one of the pipes. Works well. You could also insulate all water pipes with foam tube-type insulation, which will help prevent freezing.

Insulating the ceiling also will save heat. How much? It has never been checked. Some people say that because warm air rises, there is little point in insulating the ceiling. That may be true as far as it goes, but it is a fact that warm air (in the house) will be lost through an uninsulated barrier (the basement ceiling) to a cold area (the basement).

A good insulation to use is called Polywrap, 8 inches of fiberglass wrapped in perforated polyethylene. The polyethylene is there to keep you from coming into contact with the itchy fiberglass, and to make it easier to handle. The perforation is to make sure the poly is not a vapor barrier. But before installing it, create a vapor barrier against the ceiling by stapling regular polyethylene plastic to the ceiling. Cut the plastic so that it drops down a few inches along the side of each joist. Install the Polywrap with insulation hangers: sharp, pointed wires that are stuffed between the joists. Place them every 24 inches.

Saving heat
and lowering the heating bill is a high priority for most of us as hints of winter keep coming our way.

Even with this glorious October weather, we know the cold and snow and sleet and hail are coming, sooner or later.

The best way to save heat is: insulate, insulate, and insulate some more.

But that is only part of the picture. There are many other ways to save heat. These are the things you can do, not in any particular order of priority:

-- Seal all leak paths.

-- Change furnace filters often.

-- Lower the thermostat.

-- Cover outlet and switch plates.

-- Weatherstrip.

-- Check your storms.

Now for some details on how to do all these things. You certainly don't have to do them all at once, or do them at all. Pick and choose your projects as you go along.

-- Just what are those leaks paths, and what is used to seal them? There are a lot of them: 1. Where wires and pipes enter the house. 2. Around air ducts and exhaust fan openings. 3. Window and door frames. 4. Along baseboards.

Seal the paths with caulk. Contemporary caulks are inexpensive and very effective, and more important, they are flexible and easily dispensed from a caulking cartridge in a caulking gun.

While wire and pipe openings are best sealed on the outside, door and window frames are best done on the inside. This is tricky because such a bead of caulk is likely to show, especially if the caulk is white and the walls and woodwork are dark, or vice versa. One's helpmate might not approve, but generally draperies and/or curtains will cover such beads of caulk.

Even caulking around baseboards can be effective because air can flow through a uncaulked baseboard joint into the uninsulated cavity of an interior wall. Not only does this lose heat, but it also creates a draft.

Caulking a baseboard can be pretty unsightly, so you can simply avoid it or caulk in such a way that it is invisible. For instance, remove the shoemold (the quarter-round trim at the base of the baseboard, caulk the joint and replace the quarter round.

-- Furnace filters are only on hot-hair systems, and changing the filter once a month in winter will make the system more efficient.

-- Turning down the thermostat will save heat, no matter who tells you otherwise. In other words, you will save more heat during the down time than what you will spend bringing the heat back up.

Do this when not at home, or at night; the more degrees you turn down (5 is good, 10 is better) and the longer you keep it down, the better.

In fact, it's OK to turn the system off completely, or the thermostat down far enough so the heat won't come on until morning. A well-insulated house will not cool off much more than 10 to 15 degees over an 8-hour period, and there should be no concern over freezing water pipes, even at below-freezing temperatures outside.

-- Stores sell foam switch and outlet plate covers, and it's easy to unscrew the plate, slip on the foam cover and replace the plate. Do this on all outlet and switches, including those on inside walls.

Buy plastic plugs for plugging into an outlet; they will help reduce air loss and also keep curious little fingers out of them. Use these plastic plugs on outlets on inside walls as well as outside walls.

-- Weatherstripping all windows and doors will not only save heat but could save you a bundle of money; a well-weatherstripped window and a good storm window are essentially as good as a double-glazed replacement window. So you don't even have to think about replacements. Of course, if your present windows are ``hopeless,'' replacements make sense.

The same goes for doors. A steel insulated door is not necessary when you have a quality wood door, well weatherstripped, and a good, tight-fitting storm door.

-- Storm windows are always good to have, and most of the time they do a lot of good in saving heat. But a lot of storms are cheap or just old and loose.

So, inspect them to make sure they are tight, and the frames are caulked. Try to wiggle the sashes (the glass panels that move up and down) back and forth. If they give even 1/4 inch, it is too loose.

Then it's time to buy new storms, and consider a quality, airtight storm at $100 to $125 each rather than a cheapie at $35 to $50.

That $100 figure may sound a little high, but it cannot be helped. And, you can go easy on the budget by buying two or three storms at a time rather than all 25 (or whatever number) all at once.

Insulation is the key
On insulation: Never in the field of construction has so inexpensive a material done so much good for so many people.

That's insulation, all right, and the good it does is lower your heating bills. It applies equally in cold and warm climates.

Despite the campaign to insulate houses, and the fact that houses built in the last 30 years are proeprly insulated, there are plenty of houses wihout insulation, and more that are underinsulated.

It's prudent to check out your own house to see if there is insulation in the walls, in the attic floor, and on the basement ceiling. And, to see if it is enough.

Fiberglass comes in batts and rolls, in various widths and thickesses to fit in various places. It also comes ground up, for blowing onto attic floors or into walls.

If you are doing it yourself, the batts or rolls are best to use.

Cellulose is another insulation, made of ground-up newspaper treated to make it fire resistant. Cellulose is the ground-up type, good for blowing in walls and attic floors.

Then there are rigid insulations: Styrofoam and polyisocyanurate (isn't that a great word?) that come in sheets (4 by 8 feet) in thicknesses from 3/8 to 4 and more inches. These insulations are used in special applciations. You don't have to wrap that long word around your jaw when you ask about it; brand names include High R Sheathing and Thermax.

But instead of worrying about R factors, consider thickness instead. Generally, 12 to 18 inches (of fiberglass or cellulose) on the attic floor, and 8 inches (of fiberglass) in the basement ceiling are reccommended.

Add another 6 to 12 inches on top of that; lay the rolls or batts at right angles to the joists. Or, blow insulation up to the tops of the joists, then add the batts or rolls. Check out Owens-Corning's new Polywrap; it is 8-inch-thick fiberglass with a plastic cover that has holes for ventilation. This Polywrap not only is easy on the hands, but also makes it easy to slide it over exposed fiberglass. Other companies make batts similar to Polywrap.

If there is insulation already on the attic floor, between the joists, add to it; add enough to reach the tops of the joists and another layer at right angles to that.

Why bother with the basement ceiling? Doesn't warm air rise? Of course it does, but you will still lose heat from the warm area of the house to the cold area, if the barrier is uninsulated.

These pros take off certain clapboards or shingles, drill holes in the sheathing, usually one at the top of a space between studs and one at the bottom, blow insulation into the cavity, and replace the clapboard or shingle.

The blown-in insualtion is packed in under pressure, so there is no settling of the insulation or gaps.

Sometimes walls will have a thin piece of insulation or even plain aluminum foil set in the middle of the wall space. While these types of insulation are not as good as a wall filled with insulation, don't fiddle with it; the gain in protection is minimal.

Everything insulated, and your work is done. Hold it! What about a vapor barrier? Yes, sir, a vapor barrier is every bit as important as insulation, because a vapor barrier is an air stop; it stops the passage of air, and in the case of a heated house (heated with all that expensive fuel), it stops the passage (loss) of heat.

Where to put it? The rule is: The vapor barrier goes toward the heated area.

If you are putting insulation in the attic floor, the vapor barrier goes against the ceiling below. Fiberglass batts and rolls usually have paper or foil backing (the foil has pretty well disappeared; it is almost always paper these days, but the paper is a vapor barrier, so you install them with the backing down.

The same thing applies to blown-in insulation; you can install a vapor barrier of 4- or 6-mil polyethylene on the ceiling (that part of the ceiling that is showing in the attic between the joists).

In basement ceilings, the batts or rolls are installed with the paper up.

If you are adding insulation to the attic floor, and there is no vapor barrier under the stuff there now, you have two choices: 1. Lift the old insulation and throw it away, and proceed as if there were no insulation in the first place. 2. Forget about the vapor barrier and add the unbacked insulation. The point is, never put a vapor barrier between thicknesses of insulation.

It is impossible to put a vapor barrier in an existing wall that you fill with insulation. However, you can paint the walls (and the ceilings, for that matter) with a vapor barrier paint, or a paint that has a high resistance to the passage of water vapor. Latex primers are pretty good vapor barriers, so is eggshell finish latex wall paint. Vinyl-coated wallpapers are excellent vapor barriers.

Those certain areas are the attic and the basement. The attic should be ventilated to prevent buildup of moisture in winter and heat in summer.

Attics are ventilated with louvered vents. The old-fashioned way is with vents in each gable (end). If the roof is hipped (sloping down on all four sides and, therefor, without gables), vents are located in the soffits (the under part of the roof overhang), and sometimes with roof vents.

The modern way is with a ridge vent and soffit vents. Simple as that; and just as you cannot overinsulate a house, you cannot overventilate an attic.

The soffit vents allow air to go through them into the attic, and up through the ridge vents. Because of this type of venting, any insulation on the attic floor (between the joists) should not go into the overhang; that would not only block the soffit vents but also could cause major condensation problems.

The basement should also be ventilated, but it is necessary only in late spring, summer and early fall.

Simply opening windows and screening them will vent the basement adequately. If there are no windows in your basement, make sure there are at least small vents, preferably one on each wall.

1. The slanting ceiling on the second floor of a Cape Cod-style house is one tough area to insulate. The second floor of these types of houses has no vertical walls except at the gable ends; the other parts of the rooms have sloping ceilings.

To provide living space on the second floors, a knee wall is built on each side, ranging from two to six feet high. These knee walls provide a crawl space behind them. The knee walls and the floor should be insulated.

Those slanting ceilings are particularly difficult to fill with insulation. Trying to stuff flexible insulation into the space between ceiling and roof boards is like trying to get your kid's spaghetti foot into a shoe.

This is where rigid insulation comes in; use two-inch-thick insulation, cut it to fit between the rafters, and push it into place. If the rafters are evenly spaced, you can get a good fit. Add a second layer.

2. A cathedral ceiling is equally difficult to insulate. In fact, in an existing cathedral ceiling, it is impossible without removing the ceiling finish. Fortunately, most contemporary cathedral ceilings are insulated, and, it is hoped, the right way.

Sloping ceilings, whether in a Cape Cod-style house or a cathedral ceiling, must have an air space of about one inch between insulation and roof boards. And, to make that air space works, there must be ventilation at the top and bottom of these ceilings: a ridge vent at the top and a soffit vent at the bottom.

Done at last, done at last. And if you do everything, you can cut your heating bill up to 50 percent. Scout's honor.

Q. I know that two walls are the best way to insulate against sound transmission, but I have 3 inches of room for the extra wall. I have heard two theories: 1. Dead air space. 2. Insulation. Can you help?

S.K., Brookline

A. Both theories are valid, but insulation, if any, should go in the new wall, not between the walls. In other words, you need that dead air space.

Since you have only three inches to play with, I suggest this: Build a wall of 2-by-2 studs (actually 1 1/2-by-1 1/2 inches) and set it a half-inch from the original wall. Fill the stud wall with fiberglass insulation. The studs and space total 2 inches; then add half-inch sound-absorbing board and half- or three-eighths-inch plasterboard. Caulk all joints. That stud wall may be a little flimsy, but it will hold together well enough once the coverings are on it. And, once it is up, you could screw a couple of steel angle irons connecting the two walls.

Q. I plan to have insulation blown in the front wall of my house, but will it cause buildup of moisture and peeling paint.? The house is 30 years old and there is only an inch of mineral wool faced with foil in the attic floor, so there might be similar insulation in the walls.

DON MURPHY, Westwood

A. I don't think added insulation will cause peeling paint or moisture buildup any more than the walls have done in the past. One problem you might run into is the location of that insulation already in the walls. In the past, this thin insulation was stapled in the walls with the thought that it was adequate. Later it was discovered, particularly with increases in the cost of fuel, that it was far from adequate.

The problem is the location of the insulation. If it is on the inside wall, then more insulation can be blown in from the outside. If it is on the outside wall, insulation would have to be blown in from the inside, which is also possible. If it is in the middle of the wall cavity, one thing that might be done is to blow in insulation from the outside, forcing the thin insulation to the inside wall. An insulation installer can tell you if this is possible, practical and/or cost effective.

You can determine what is in the walls, and where, by pulling a double outlet from its electrical box in the wall. Turn off the power first, then take off the outlet cover, and pull out the outlet. You can peer through the holes in the box, or poke with a coat hanger to feel what's there.

Q. I bought an old clapboard house with no insulation. I thought of having the insulation blown into the walls, but I don't like the idea of drilling holes in the clapboards (to allow insulation to be blown in), then patching them, because the patching will show. Could I take the clapboards off, drill holes and insulate, then put them back?

R.R., Newburyport

A. Removing selected clapboards, drilling holes in the sheathing and blowing in insulation is the way it's done. I have not heard of drilling holes in the clapboards because it is not necessary, and if you find someone trying to do it, stop him fast. To be sure, insulation contractors usually split the clapboards to remove them, but when they put them back, the splits don't show.

Q. Blown-in cellulose insulation in my attic floor is dusty, and I'd like to use part of the attic for storage, putting plywood on the floor where needed. What can I put over the cellulose to keep the dust down -- poly or Tyvek?

ERIC YOUNG, Concord

A. Use Tyvek, or Typar, similar materials that allow water vapor to go through it but not air, making it ideal as a dust cover. Staple it loosely on the joists to keep it from billowing. The plywood can go on top of the Tyvek. Polyethylene is a vapor barrier, and in that position; could trap moisture under it. Nail the plywood lightly, to keep it from moving as you walk on it.

Q. My house is a year old and has vinyl siding. We call it the Tupperware House. It has three steel doors, and the mud room is 50 percent glass, another is all glass. I am feeling cold air where the doors meet their frames, and the windows I think are also losing a lot of heat. I paid $139 for gas heat in December. Is there any way I can stop those cool breezes and perhaps shield the windows against all that heat loss?

L.S., Framingham

A. The Tupperware house is probably pretty tight with all that plastic wrap around it. The doors should be tight, being insulated and factory-weatherstripped.

Let's tackle those doors first. They may not be leaking air, and the way to find that out is to place a match flame near the seam where door meets frame. If the flame moves either way, toward the seam or away from it, you have an air leak. If the flame continues straight up, then the door is as tight as it will ever be.

If there are leaks around the door, you can apply self-sticking weatherstripping around the frame on the outside. It will give added protection, at least.

If the doors are tight, confirmed by the match-flame trick, they may be creating their own draft. Huh? Yes, if the door is cool, warm house air will cool off when it hits the door and, as it cools, it drops, replaced by more warm house air to continue the downard cycle, creating the draft. There is little you can do about that on a steel door.

As for the windows, rooms half glass or all glass are big heat losers, even with double-glazed windows. You could install Window Quilts, widely sold in stores, on the windows. They fit tightly, and you can get opaque or translucent Window Quilts, which will make a big difference.

Regular draperies, especially insulated ones, will also work, but they must be secured to the frame on all four sides: top, sides and bottom. If they just hang against the window, with space between drapery and frame, they can make things worse. If there is a space between drapery and frame, warm air in the room can flow into the space and cool off. As that air cools, it pulls more air down into the space.

An alternative to Window Quilts is storm windows, interior or exterior. You can put exterior storms on a vinyl frame. It might be easier to put in the inside storms because the casing (frame around the windows) is wood, so the storms are more easily mounted.

Q. My living room is on a concrete slab, padded and carpeted. Is it worth trying to put anything on top of the slab, as insulation, maybe?

M.C., Framingham

A. Probably not. If you think the floor is cold, and there is no radiant heat in the slab, try this experiment to see if there is any heat loss through the concrete: Put your hand on the slab, if you can find a bare slab to touch. If not, put your hand on the carpet. Hold it there for a minute or two. It will feel cold at first, but if your hand warms up, or what you're touching warms up, it means that the slab is insulated; even the carpet and padding provide some insulation. If your hand feels as cold after a minute or two as it was when you first touched the floor, it means that the slab is not insulated and is pulling heat out of your hand, just as it is pulling heat out of the house.

Trouble is, it is difficult to insulate that slab. If you are comfortable in the living room, and are not paying excessively for heat, then live with it. If the house is less than 20 years old, it may have insulation under the slab. At least it should.

The only way to insulate the slab is to take up pad and carpet, put down 6-mil polyethylene, put down 2-by-4-inch sleepers on their wide side, 16 inches apart (have them gunned in professionally), then install 1 1/2-inch Styrofoam insulation between the sleepers, cover them with plywood and finally replace the pad and carpet. You have to do this because it's the only way to stop water vapor from coming up through the slab. You can't do this if there are heating units in the slab.

Of course, this will raise the floor by 2 inches, and if you have baseboard heating units, you have to move them, too. In a nutshell, try to live with the situation if it is not too troublesome.

Q. My living room is on a concrete slab, padded and carpeted. Is it worth trying to put anything on top of the slab, as insulation, maybe?

M.C., Framingham

A. Probably not. If you think the floor is cold, and there is no radiant heat in the slab, try this experiment to see if there is any heat loss through the concrete: Put your hand on the slab if you can find a bare slab to touch. If not, put your hand on the carpet. Hold it there for a minute or two. It will feel cold at first, but if your hand warms up, or what you're touching warms up, it means that the slab is insulated; even the carpet and padding provide some insulation. If your hand feels as cold after a minute or two as it was when you first touched the floor, it means that the slab is not insulated and is pulling heat out of your body, just as it is pulling heat out of the house.

Trouble is, it is difficult to insulate that slab. If you are not uncomfortable in the living room, and are not paying excessively for heat, then live with it. If the house is less than 20 years old, it may have insulation under the slab. At least it should.

The only way to insulate the slab is to take up pad and carpet, put down 6-mil polyethylene, put down 2-by-4-inch sleepers on their wide side, 16 inches apart (have them gunned in professionally), then install 1 1/2-inch Styrofoam insulation between the sleepers, install plywood and finally the pad and carpet. You have to do this because it's the only way to stop water vapor from coming up through the slab. You can't do this if there are heating units in the slab. Of course, this will raise the floor by 2 inches, and if you have baseboard heating units, you have to move them, too. In a nutshell, try to live with the situation if it is not too troublesome.

Q. I had an 18- by 18-foot addition built last year; the floor joists over the basement are 2 x 10s with 6 1/4 inches of fiberglass insulation, with a vapor barrier up against the floor above. There is still plenty of space for more insulation; can I install 3 1/2-inch backed insulation in that extra space? Or is a second vapor barrier taboo?

CHUCK SANTORO, Millbury

A. A second vapor barrier is, indeed, verboten. But there are ways to beat it. One is to put up the backed insulation, stapling it the bottom of the joists. Then, make lots of holes in the backing paper with an awl, ice pick or other pointed tool.

Or, take down the insulation hangers on the insulation already there, put in 3 1/2-inch unbacked insulation, and reinstall the hangers. If you are concerned about exposed fiberglass, you can staple Tyvek to the bottom of the joists. Tyvek is not a vapor barrier; it allows water vapor to go through it, which is good, but stops the passage of air, which is also good because it will add to the effectiveness of the insulation by preventing heat loss. The Tyvek, being white, will also lighten up the basement by reflecting light.

Q. I am buying a house with 2 x 3 studs against the concrete foundation, with friction-fit insulation between the studs. I know there should be a plastic vapor barrier on the wall, but where should it go: in front of or in back of the insulation?

CHRIS CLANCY, Natick

A. Any vapor barrier -- plastic, paper, or foil -- always goes on the wall facing the basement, or in the words of insulators, facing the heated part of the room. Put the plastic on the face of the studs, so that when it is installed and you are in the room looking at the wall, you will see the plastic. Cover the plastic with plasterboard or any other wall finish such as paneling, and you will be done with that wall.

The 2 x 3s instead of 2 x 4s are OK, because a room below grade does not need as much insulation as a wall above the ground.

Q. I plan to remove the insulation between the rafters in my attic and put insulation in the attic floor. There are floorboards in the attic; I plan to blow in granulated insulation under the floorboards. Will that work?

DAVID JERISON, Belmont

A. Taking the insulation from between the rafters (the sloping beams holding up the roof) is a good idea because it is doing little good there; heat is being lost through the floor and is being stored in the attic; in other words you are heating the attic for no good purpose. And that goes doubly if the attic is ventilated.

Blowing insulation under the floorboards is good, but be sure that no insulation gets into the eaves (the underpart of the roof overhang). Insulation in the eaves could cause condensation of water vapor into water, a serious problem in an attic. It also could cover any soffit vents (the soffit being the horizontal underside of the eave), and that is not good.

To prevent this, install baffles at the ends of the joists where they form the eaves. Better yet, bite the bullet, pick up the floorboards (no easy task, admittedly), and install fiberglass batts, or rolls, with the paper backing (a vapor barrier) against the ceiling below. The vapor barrier is important in keeping heat in the house where it belongs. Insulation by itself, while important, is not enough.

Then put the floorboards back. Sure it's a lot of work, but the job will be done right.

Q. Is urea formaldehyde insulation against the law? My son wants to buy a house in Michigan and the owners disclosed that they think U-F is in the house. What should he do?

ANXIOUS CALLER

A. It is not exactly against the law, but installation of U-F is; and it is no longer installed. Houses that already have it are not breaking the law, but some states require that it be removed before the house is sold, even if it is not causing problems. The reason for the controversy dates back nearly 20 years, when some U-F was defectively installed, causing allergic reactions to people who were sensitive to it. So, it was banned.

Your first priority is to have the insulation checked; if it is not U-F, there's no problem. If it is U-F, it should be removed and safe insulation installed, but at great cost; if your son can reduce the house price by the amount needed to remove the U-F and put in new insulation, that might be a good idea. Short of that I suggest he look elsewhere.

Q. I have a garrison Colonial with a large overhang in front, with soffit vents in that overhang. I found some bees behind the vent, and then discovered a 10-inch-high space between ceiling of the first floor and floor of the second. I can see between the joists all the way to the back of the house. Isn't that space quite cold and causing excessive heat loss? It doesn't seem cold indoors and the heating bills are not high. What can I do about that space? I took care of the bees.

S.S., Pepperell

A. First of all, chances are that your insects were hornets or wasps, and if so, they die off in the winter, unlikely to occupy the same nest next year. If they were honey bees, they could be making a hive, which could actually bulge the walls.

At any rate, you are, indeed, losing heat because of that open space between ceiling and floor; the vents aggravate this loss of heat. I suggest filling the entire cavity, back to front, including the overhang, with 10-inch-thick fiberglass insulation. No vapor barrier is needed in this case. Normally you would not put insulation in an overhang, but since this is not a roof overhang, it is OK. And I don't think the vents are necessary there; you can leave them as is, or cover them. If you did not fill that overhang with insulation, the vents would allow cold air to go right against the floor above the overhang, not a good situation.

Q. The insulation between the rafters of my attic is coming down, and when I went to put it back in place, I noticed the roof boards are wet. I certainly don't want to put insulation against wet boards, but what is causing that wetness? I checked, and the roof is not leaking.

J.McK., Northborough

A. The wetness is condensation, caused by moisture being caught between the insulation and the roof boards and condensing against the cold boards. It is cured by removing the insulation and putting it, or other insulation on the attic floor, between the joists. I suggest enough insulation to fill the space between joists right to the top of the joists. Also, put a vapor barrier (kraft paper-backed insulation or a separate piece of polyethylene plastic) directly against the ceiling below. Another part of the cure is to ventilate the attic, with soffit vents (the soffit is the underpart of the roof overhang) and a ridge vent.