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.

Insulating a basement

Q.  My basement is basically unheated. Would it be advantageous to put insulation around the ductwork or to insulate that particular space between the floor joists where the ducts are? Also, I notice that above the foundation where the end cap 2×10 is for the floor joists, it seems colder than the rest of the basement. Can I or should I put some sort of insulation against this end cap? Could I use rigid foam?

A.    If your basement has any appliances such as the furnace or boiler, a clothes washer and dryer, or you use it as a workshop, it is best to insulate its walls, but do not do so lower than three feet below the outside grade unless you are sure that the foundation has a working drainage system and that it has been backfilled with coarse material for good drainage.

Insulating a basement or crawl space all the way to the floor is taking a risk that frost may go down deep and crack the walls unless the steps mentioned above are in place.

If your basement is not used at all, insulating between the floor joists is an option. You should, however, case the ducts and pipes into a chase and insulate the exterior of the chase so that heat from the first floor can keep the pipes and ducts warmer.

Regardless of what you decide to do, you should insulate the band joists (which you call the end cap), as there is a great deal of heat loss through them (one percent or more of the total house losses in such a small area, according to some authoritative studies.) You can do so with fiberglass batts with an integral vapor retarder, or unfaced batts that will need to be covered with a plastic vapor retarder.

Or you can use rigid foam. If you choose  foam, use boards that are two inches thick and caulk their perimeter once you have set them in place. If you choose fiberglass, cut the batts one inch longer than the depth of the joists (to ensure a tight fit), push them in against the band joists without squeezing them, and staple the edges of the integral vapor retarder or the plastic to the floor joists. Be aware that if you do not use a vapor retarder, moisture will migrate through the fiberglass and condense against the cold band joists; this will lead to potential rot.

Home inspector misses problems

Q.  My husband was in the attic recently solving a few problems with our SpacePak AC in the attic. He found that both of the bathroom fans in our 1956 ranch home vent directly into the attic – in fact, there are no vents from the fan. In the attic, he found one just had a bag over the fan.

We bought the house in 2006 and we did have the home inspected. I dug out the inspection report, found the “attic”section, and this is what it said in the section labeled (1) “Exhaust fans exhaust outside” – the “cannot view” was checked. My husband saw them, why couldn’t the inspector? (2) He made comment at the end “Vermiculite insulation in the attic.”

No mention of possible asbestos was ever mentioned verbally or under the “general comments” summary review of the inspection.  If the word “asbestos” had been uttered, remediation would have required for me to buy this house or the deal would have been killed.

I wondered about the vermiculite comment and Googled it. It took two seconds to connect to the EPA and info on how 70% of vermiculite insulation in the country came from the mine in Libby, Montana and how asbestos was also in it – up until 1990, when the mine was shut down. “Assume vermiculite insulation has asbestos in it” was the general idea.

The other question I have is if the Space Pak AC with its vents in the ceiling can blow any of the air from the attic into our living space.

If you are wondering, yes, the home inspector was recommended by the real estate agent of the owners.  We were not represented by a real estate agent.  We had the home inspected, and a lawyer represented us at the closing.

Was the home inspector negligent in not mentioning this insulation and its possible connection to asbestos?  My husband was with him during the home inspection and does not remember even going into the attic. I am now wondering if he saw the vermiculite insulation in there and didn’t really enter – perhaps the reason why the “Cannot view” comment regarding the exhaust fan vents from the bathrooms.

Where should I send the insulation to be tested?  I am not sure how to proceed with this.

A.    It does look as if the home inspector was not thorough or attentive to details on his own reporting form.

If he could not see the outlet jacks of the bathroom fans on the outside of the house, and  reported that by checking the “Cannot view” box, he should have been especially careful to inspect the attic to see how they were vented, if at all.

He should also have mentioned the possibility that the vermiculite contained asbestos.

If the SpacePack system was properly installed, and the ceiling cutouts caulked around the ducts, there is low probability that attic air is entering the conditioned spaces.

Your experience with the real estate agent-recommended home inspector is familiar. In my professional experience, I have seen quite a number of cases where the real estate agents recommend less-than-thorough inspectors because they “find” fewer problems. On the other hand, there are many real estate agents who only recommend the top inspectors. So it’s a question of whom the sellers chose as an agent.

It is far better and safer for the buyer to choose the inspector after doing some research. The wise course is to choose an inspector certified by one of the two prominent professional associations: ASHI and NAHI.

To have the insulation tested, if you feel it necessary, call environmental firms listed in your Yellow Pages. You might simply assume that it does contain asbestos unless you plan on having it removed and replaced – a huge expense.

An alternative is to have it covered with blown-in cellulose after the bathroom fans have been properly vented to the outside.

Adding insulation to crawl space

Q.    We have a crawl space underneath one room and it has batt insulation and only chicken wire covering it. One question is can this insulation get mildewed? Sometimes we can smell an odor in this room but not sure if it is coming from underneath. Not sure how long this insulation has been there but it is fairly dirty and I assume that some moisture would be present in it.

Also, along with replacing it with more batt insulation, can a rigid board cover the new one for better protection? Thank you.

A.    Is the crawlspace floor covered with 6-mil plastic to contain the soil’s moisture? If not, it should be. The perimeter of the plastic at the foundation should be weighted down with either a bit of the soil, a few brick batts, or pieces of pressure-treated wood scraps. All seams should be generously overlapped by at least two feet.

If there is some leakage from outside, the plastic should be brought up the foundation walls to a line above the outside grade and taped or otherwise fastened to clean walls. The plastic must be laid so that water leaking is directed below all seams in the plastic. For example, any plastic laid in the center, over the plastic around the perimeter, must be laid on top of the perimeter pieces.

If the existing fiberglass batts are dirty, it indicates that they may have been subjected to air movements. Do you have crawlspace vents in the foundation, and are they open permanently? Once the soil is thoroughly covered with plastic, you should close or seal these vents to keep air out. You can install pieces of rigid insulation in them.

From time to time, give the crawlspace the nose test; it should smell OK. If the fiberglass batts feel dry, there should be no need to replace them, as they are non-absorbent. Any moisture on the fibers would be there simply as a result of surface tension.

Once you have made the suggested corrections, there is no need to replace the chicken wire with a rigid board. Unless the rigid board material you would choose is moisture permeable, it could trap any living space moisture migrating through the floor system in the joist cavities and cause problems.

Caulking the bottom plate of walls

Q.    I think our house leaks – both cold air in and warm air out — at the area where the structure and siding sit on the concrete slab (no basement). I believe there is nothing to seal the exchange of air at the 200 feet of this contact. Is there a product like a putty to build up an insulation barrier? I realize I would have to work with my head on the ground to install whatever product is recommended.

A.    It does sound as if there is no sill sealer under the bottom plate of the walls. You can try to caulk the perimeter from outside, but it may be a lot easier to caulk the joint between the concrete slab and the wall plates from inside, if you have access to it.

Use polyurethane caulking, which you can buy in construction specialty houses like A.H. Harris:

Insulating a home built with terra cotta blocks

Q.  We have an old house made out of terra cotta block from top to bottom. We recently insulated the inside walls with R-13 and drywall. Then we had our outside done in vinyl siding and the foam insulation 3/4 inches thick. Our house is still a little chilly at 69 degrees. Any suggestions on how to keep our house warm? Also we were going to invest in a pellet stove. Any suggestions on this?

A.  I assume you studded the inside of the house’s exterior walls and put R-13 fiberglass between the studs. That, together with 3/4-inch rigid foam, gives you  walls with only R-17 – not too exciting for a cold climate.

There is also the possibility that convective currents within the terra cotta blocks rob you of some of the R-factor. This is difficult to overcome unless the blocks had also been filled with insulation.

It would have been preferable to apply 1-inch thick rigid foam insulation directly to the terra cotta walls and then stud the walls, if you have the space, with 2-inch by 6-inch studs and R-19 fiberglass insulation. Then outside, I would have used 1-inch thick rigid insulation instead of 3/4-inch. This would have given you an R-29 plus.

Now it seems as if your only option is to get warmer with a pellet stove. Pellet stoves are very effective and, as long as pellets are readily available at reasonable prices, they are a good way to go.

Insulating a stone foundation

Q.    I was going to insulate a stone foundation on an 1830s farmhouse with spray foam. but I seem to remember you answering a similar question and suggesting using fiberglass insulation instead. I was going to insulate from the sill plate to 18” – 24” below grade, 1” thick spray foam. What would you recommend? And if fiberglass, should it be 3 inches or 6 inches thick and faced or unfaced? Thank you for your help.

A.    Spray foam is fine if you can afford the cost. The walls would have to be very clean for the foam to adhere to them, and if there is occasional moisture seeping through them, I wonder if the foam would delaminate from the stones.
Fiberglass would not require that the walls be clean, and moisture would not hurt it, as fiberglass is hydrophobic. Any actual water would run down to the floor.

If your cellar floor is dirt, I would not recommend insulating the band joists with fiberglass, which would prevent any drying in case moisture from the ambient air comes in contact with the sills and is not allowed to dry; they need to be exposed to the air. However, you could insulate them with spray foam, but is it worth the cost to have a foamer come simply to do the band joists? Keep in mind that the canned foam you can buy in hardware and building-supply houses is for sealing cracks and has very little insulating value, but it would be better than doing nothing if you put a lot of it on.

If you decide to use fiberglass, staple the top of the batts to a pressure-treated 2×2, 1×3 or 1×4 screwed or nailed to the bottom of the sill beam and let it hang down to the 18″ or 24″ inches below grade you have in mind.

You should find a way to staple the bottom of the batts to a pressure-treated wood strip fastened to the stone walls to make it more effective. If the stones in the walls are mortared, and the mortar is sound and in good enough shape, it may be possible to use masonry nails, but it might be best to clean the most prominent stones and use a construction adhesive to fasten the wood strips. It does not need to be very regular. You can insert some batting to close the spaces between the wood strips and the stones if the gaps are large.

R-15 (4-inch ±-) batts are easier to handle and should be sufficient. Faced with aluminum would be preferable. Staple the flanges of adjacent batts together.

If the floor is bare soil, it should be thoroughly covered with 6-mil plastic. If there is some leakage through the walls or at their base, try to deal with that from outside to eliminate it, but also dig a small trench around the inside perimeter. Use the dirt to make a small berm and wrap the berm with the plastic, but not the bottom of the trench.

Re-siding an old farmhouse

Q.    My husband and I recently purchased an 1820 farmhouse and plan to put in new windows, plus new pre-primed cedar clapboards. We will use the Home Slicker with Typar. Our question concerns the following: The house is built with vertical planks, two to three inches thick, which are essentially slabs of wide trees. There are gaps between the planks, as they are irregular in shape. Do you suggest that we cover these planks with plywood before using the Home Slicker?

A.    There is no need to use plywood over the planks unless the gaps are very large; anything up to an inch should not matter. The Typar is a windbreaker and the gaps will help the house breathe if there is no air barrier/vapor retarder on the inside of the exterior walls.

You haven’t mentioned insulation or the inside finish. Is there any insulation on the living space side of the planks? If not, and there is no way to do so from the inside, you may want to consider installing 2-inch thick rigid insulation over the planks followed by 5/8th-inch CDX plywood sheathing onto which the Typar/Home Slicker can be stapled. Even though clapboards should be nailed onto studs, since you will providing a rain screen behind the clapboards, they should be OK nailed to the plywood.