Vapor barriers for a cathedral ceiling

Q.  I recommended to a friend that he have his insulating contractor put up a poly vapor barrier over the Kraft-faced fiberglass insulation in his cathedral ceiling. His contractor said that would be a bad idea because it would form a double vapor barrier, bad besides, because the Kraft facing is a good vapor barrier on its own. Who is right?

A.  You are right! The combination of the Kraft paper and the plastic would be on the warm side of the roof, therefore no condensation would occur. The contractor is wrong! Kraft-paper vapor retarders are very poor, and I have seen quite a number of cases where they have caused serious problems in cathedral ceilings.

Your friend should insist on the application of a 6-mil plastic vapor retarder and should thank you for preventing real problems down the line. One prominent case I have dealt with was a beautiful new house with Kraft-paper fiberglass and tongue-&-groove ceiling in which the ceiling had to be torn down to make repairs, as it was “raining” inside on cold days.

The contractor should have used unfaced fiberglass with plastic, or, better yet, fiberglass should not be used in cathedral ceilings at all. The only safe insulation in these confined spaces, with usually inadequate means of  ventilation and control of convective air movements, is closed-cell polyurethane.

Painting ceiling tiles

Q. I would like to know if I have to use a sealer to paint over a ceiling that has 9 X 9-inch ceiling tiles with a swirled texture. I do not know what the tiles are made of but the ceiling has been up for over 30 years and has never been painted before. Ceiling-tiles

A.  The ceiling tiles have probably accumulated dust and other pollutants over 30 years. Vacuum them with the soft-brush attachment. If the tiles are dirty and spotty, you may want to clean them with Absorene Wall Cleaner, a non-toxic dry cleaner that works on ceiling tiles. If you don’t see it in a local hardware or home store, check The site lists stores that carry it as well as filling orders on-line. Special ceiling tile paints are available and can be sprayed or rolled on with care. Check your local paint stores.

Insulating rooms over the garage

Q.  I have two bedrooms over an unheated two-car garage with finished ceiling and 2-inch foil-backed insulation (house built in 1968). I would like to add more insulation since the rooms are cold, but have been told that insulation cannot be blown in over the existing insulation because the blown-in material will “stick” and not fill the void. Others have said that should not be a problem and to go ahead with the job. Who is right?

A.  The rooms above are cold because the joist cavities of the garage ceiling are most likely empty. Insulating the garage ceiling with 2-inch thick rigid insulation did nothing for the rooms above; it only insulated the garage.

There should be no reason why you can’t have cellulose blown into the joist cavities. Select an experienced insulation contractor who will blow in the cellulose carefully to ensure that the entire cavities are filled and make the necessary patch up repairs once the job is done.

Painting over mold stains

Q.    We had a new home built and after we closed, we noticed spotty areas of mold on the ceiling of our unfinished basement. Either the wood used already had the mold on it or it occurred during the construction process when they closed up the basement without adequately drying it out. The builder was pretty responsive and hired a mold remediation company to clean it up. After they completed their process we were left with “mold stains” on the wood. It is a year later and there is not further growth. Should we paint these areas? We do not want any problems selling the house in the future.

A.    The mold developed because of the high level of moisture exuding from the concrete and other components of the building process. You are fortunate in having had a responsible contractor who took care of the problem. You certainly can paint the basement ceiling to make it more attractive. Prime first with a stain blocker like B-I-N.

Insulating bedroom floor over unheated garage

Q.    My bedroom is located over an unheated garage. The unfinished garage ceiling is insulated with two layers of rolled bat insulation. The paper vapor barrier is facing the garage, not the bedroom floor.

I would like to seal off the garage ceiling with foam boards to stop any cold air from coming in through the bedroom floor and to provide some additional insulation. My understanding is that the vapor barrier should be next to, or on the side of, the heated room. Does this hold true for my bedroom/garage situation? Must I reinstall the insulation with the vapor barrier next to the bedroom floor before I put up the foam board?

A.    Ideally, yes but we know that paper vapor retarders are not very effective. Moreover, the addition of at least 1-inch thick rigid insulation will warm the joist cavities and reduce the chance of condensation within them. It will also reduce any heat loss through the floor joists.

And if your sub-floor is plywood, that in itself is an effective vapor retarder. However, pull down some of the fiberglass insulation in a few widely scattered spots, particularly next to the outside walls, and check for any signs of moisture or mold development. If you find any of these, you should seriously consider pulling the insulation down wherever these conditions are visible, allow the areas to dry and put the insulation back (if it is dry) with the paper vapor retarder facing the bedroom floor.

Be sure that the entire joist cavities are filled with fiberglass insulation to prevent heat loss and cold air from infiltrating between the top of the insulation and the subfloor. You are unlikely to find that the entire area has been affected.

Also be sure that you use extruded polystyrene rigid insulation (XPS — blue, pink, grey or green). Remember that rigid insulation on the garage ceiling will have to be covered with fire-code drywall, properly taped.

Nailing molding to ceiling

Q.    What is the best way to nail molding to the ceiling without making hammer marks?

A.    There may be a number of techniques, but here is my suggestion: Don’t drive the nails all the way in; stop a very small fraction of an inch short of driving the nails home. Use the right size nail set to finish driving the nails and countersink them slightly so you can putty over their heads. Use a finish hammer (lighter than a regular hammer) and tap the nail set in gently.

Another way is to use a piece of aluminum (with a hole in it for the nail) that you hold over the molding until the nails are driven almost completely flush with the trim. Finish by setting and countersinking the nails in with a nail set.

Installing light fixture on a ceiling that has heating cable

Q.    We have electric ceiling cable heat. In our living room, we want to add a chandelier but we are concerned if we can do it with ceiling cable. Our house is 30 years old and it does not have any light fixture on the ceiling presently.

A.    I assume that you will have a licensed electrician do the installation, as you should. The safest way to do what you want is to use wire mold, but extreme care must be taken not to hit one of the ceiling wires with any driven fasteners. For that reason, it is best to use adhesive.

Cold air comes in through recessed lights

Q.    My house is only nine years old and well insulated with one exception. The recessed lights that are in many areas throughout the  house allow a significant amount of cold air into the house in the  winter time; in fact, probably as much draft as one would find in a very old house.

I have asked for advice, and all I hear is that you can’t put insulation around these lights, and the only solution, an expensive one, is to replace them with the newer recessed lights that don’t permit air to go into the house. Do you have an inexpensive solution for this?

A.    Those who recommended changing to lights that “don’t permit air to go into the house” are referring to IC fixtures (IC stands for insulated ceilings). These fixtures can be covered with insulation and would be the best solution to your problem.

You didn’t say but assuming that you have flat ceilings and access to the attic, I’ll pass onto you a system a mechanical engineer friend and I devised years ago to solve this very problem. You can build a collar with 24-inch wide stock aluminum coil roll. Make the collar 24 inches in diameter and fasten its ends with sheet metal screws or pop rivets. Place this collar on top of the existing attic floor insulation Put a sheet of aluminum on top of the collar. Wrap R-13 fiberglass insulation around the collar and place the same type of insulation over the aluminum sheet.

This leaves enough air space around the fixture for the heat generated by the bulb to dissipate while blocking cold air from getting through and providing an insulated jacket. Be aware that this is not a procedure recommended by building codes.

However, if you have cathedral ceilings, there are only four solutions: Replace the fixtures with IC fixtures; replace them with surface mounted fixtures after insulating around the new electrical boxes and repairing the drywall; remove them entirely and patch the ceiling; or live with the problem.