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.

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.

Frost causes cracks in foundation

Q.    I have a room in the basement that was built as an addition afterwards by previous owners. Above it is a cement parking area. The area is damp in the summer so I use a dehumidifier. With this long winter in Canada, with thaw and freeze cycles, I have noted cracks in the foundation bricks. Prior it was treated with Zinsser WaterTite Waterproofing Paint.

The ideal situation is to excavate from the outside but it is not my property and the expense is high for a non-used room.


  1. Should I continue to use the Zinsser WaterTite for repair?
  2. Should I look at supporting inside foundation with cement brick foundation on 3 sides?
  3. What do the cracks indicate?

See attached photos [reproduced below]. Any suggestions would be appreciated!




A.    The cracks indicate that frost pressure from outside has pushed the walls in slightly. This may have been caused by extensive water penetration, perhaps from a negative-grade condition outside, which could include the parking area. If the ground and the concrete slope toward the foundation, rain and melting snow in sufficient amounts can saturate the soil, and frost does the rest.

A dehumidifier is fine to use in the summer to lower the relative humidity, which could cause molds to grow.

Painting the inside of hollow block walls with waterproofing coatings is a bad idea. Water can accumulate in the blocks’ cores and cause serious moisture problems in the living areas. I would not recommend using any of these coatings.

The photos you sent do not show that the situation is very serious at this time. But recurring yearly events are likely to aggravate the situation.

The outside grading should be examined carefully, and so should the slope of the parking area. Adding soil to change the slope of the grade is relatively simple, but the concrete area is more involved. Discharge from downspouts should also be checked to make sure that it does not remain close to the foundation.

Since this is not your property, any repairs should be the responsibility of the owners.

Types of insulation to use in a cinderblock basement

Q.    I know you’ve given advice in the past about basement insulation but I have some questions. I’m working on a ’60s ranch house with a typical cinderblock basement. Lately I’ve read and heard that it’s better to insulate rim-joist pockets with rigid insulation versus batt insulation because of moisture and dampness from the cold. Is that right?

Then my next question, is it better to use rigid or batt insulation between the studs and to complete the work with vapor barrier and drywall?

A.    Rigid insulation at the rim joists is fine as long as it is installed very tightly and caulked around its perimeter to prevent moisture by-pass. R-19 or greater fiberglass insulation with a plastic vapor retarder applied over it and stapled tightly all around also works well.

I do not recommend insulating any foundation, especially cinderblocks, lower than 2-feet below grade unless you are certain that:

  1. You have a functioning foundation drain;
  2. The backfill around the foundation was done with coarse, well-draining material and, most importantly;
  3. The grade slopes away from the foundation for the water to drain away quickly.

It also helps to have a healthy stand of grass to draw moisture from the ground. Insulating deeper without these conditions risks cracking the walls from deep frost penetration.

The choice of which insulation to use on the walls is up to you. Rigid insulation is applied directly to the walls with adhesive, and the studs are set against it. If fiberglass is chosen, the studs should be set 1-inch from the walls, strips of insulation cut to fill these spaces, and unfaced insulation pressed in place between the studs to fill the entire spaces between the walls and the inner faces of the studs. A 6-mil plastic vapor retarder should be stapled to the studs and drywall applied over it.

Improvements to a dirt-floored foundation in an old house

Q.    We live in a home built about 1880. The basement foundation is of stone upon which is a post and beam framing. We covered the dirt floor with some sand, for cushioning for a thick polyethylene sheeting, out to the base of the walls. We patched up holes and cracks in the interior walls, and also in the exterior walls to the extent we could access it without digging.

The dehumidifier runs constantly at a setting of “5.” We have an electric baseboard heater on low in the area of the water system.

My questions are:

  1. We wanted to cover the fiberglass insulation, which is around the sill board, for appearance but also for heat retention. How helpful would it be to cover it and the stone wall with a thick polyethylene sheeting?
  2. As the floor boards are cold on the ground floor, would it make sense to attach some material to the underside of the floor in the basement?

A.    The poly sheet you propose to install over the fiberglass insulation at the sill will provide a vapor retarder to keep moisture from migrating through the fiberglass, causing condensation to form on the cold wood. So this is a good idea.

However, the plastic will not do much for the stone walls. The best thing you did was to install a thick sheet of poly on the floor as a lot of moisture comes from the ground. I would not recommend adding insulation between the first floor joists. In an old house, the old wood members must be kept open in order to dry.

The best procedure to make your first floor warmer is to take a page from the old-timers: get some mulch hay bales from local farmers and stack the bales tightly against the foundation. Cover them with plastic so they won’t get soaked if it rains a lot. Remove them in the spring and store them safely so they can be reused next fall.

Repairing foundation problems that were hidden by house seller

Q.    I purchased a house about 8 years ago. After I moved in, I discovered the basement retained water, this was a question I asked the seller before I purchased the house, who said it did not get water.

I had an inspection done before purchasing, but the seller did a good job of hiding the fact. In any case, I finally saved enough money to have French drains put in.  The contractor advised me to take the drywall off the wall in the basement, in case there was any mold (putting up this wall was one of the ways the seller hid a defect in the foundation).

When I took the drywall down (it was the only wall the former owner had drywall on), I discovered a bulge and a shift in the foundation of approximately 3 inches out and approximately 6 feet long. How do I go about repairing this problem?

A.    First, you have a claim against the former owners; sellers are required by law to divulge defects, and not only did they not divulge the leakage and wall problem, they lied when you asked them! The real estate agent may also bear some responsibility but that is questionable. Finally, did the inspector miss something — such as water stains at the base of the gypsum wall (unless the wall was installed just before the sale and no leakage occurred after that).

There could also have been some other signs but, unless you have photos taken at the time of the inspection, it may not be possible to prove that there was something suspicious on the wall after eight years. The training and experience of the inspector are always very important in hiring one.

The surest way to get an experienced inspector is to look for one who is a fully certified member of ASHI (American Society of Home Inspectors). To find one, visit ASHI”s Web site at: and follow the prompts under “Find a Home Inspector.”

A 3-inch displacement in what I assume is a block wall is quite serious. If it is on a bearing wall, it can lead to structural collapse. This is not something for you to fix yourself. You need to have an experienced contractor (or an experienced mason) investigate the best procedure for repairs. The fact that the bulge and shift are only six feet long is a plus, and it may make the repairs easier and less costly. When you have all the answers, decide whether or not it is worth talking to an attorney.

Crack between sidewalk and foundation comes back yearly

Q.    There is a crack between the house foundation and the sidewalk. I keep filling this crack with cement almost every year but it comes back again. A contractor told me that there is nothing that can be done about it. The problem is that I see moisture on the foundation walls inside the basement. Any advice, please?

A.    There is obviously seasonal movement that breaks down your repair. It sounds to me as if your sidewalk is slanted toward the house foundation so any rain water gets into the crack and wets your basement wall.

The ultimate solution is to have the sidewalk redone to slant away from the foundation. This can be done by adding a new layer of concrete (if your sidewalk is concrete) or covering it with brick pavers or flagstones, or by removing it and starting all over. A potential problem with covering an existing concrete or other masonry sidewalk is what happens if there are any steps to the house, etc. An experienced masonry contractor should be able to advise you and make the necessary corrections.

However, if the slant is minimal and you do not, or cannot easily, make the changes to the sidewalk – and the crack is small enough — you could try this: Thoroughly clean the crack as deep as you can. Carefully insert in it a backer rod of the right size without breaking its skin so that the depth of the crack left for caulking is half the size of its width. Buy polyurethane caulking (nothing else) and caulk the crack with it. You can buy backer rods and polyurethane caulking from firms specializing in construction supplies.

Water seeping into corner of basement

Q.    We have a finished basement that has water seeping in at one corner. We looked into having an interior drainage system put in, but it is cost prohibitive.  Someone recommended we install an exterior sump pump to draw the water away from the house. Have you ever heard of doing this and is it effective? Are there any other alternatives?  And most importantly, how do we find a contractor that has experience with this kind of work?  We would really appreciate your advice.

A.    The first thing anyone with basement leakage must do is to check (or have checked by a knowledgeable person) the grade around the house. That includes any appurtenances such as patios, walks, driveways, etc. All flat or negative (sloping toward the house) grade must be corrected to shed water away from the foundation. This may require quite a bit of work if appurtenances need to be altered.

Not knowing your site, I can only say that whoever suggested an exterior sump pump has a great imagination. I have never heard of that before. Condo projects do have deep drainage systems if there is a lot of water to dispose of, but they generally lead to a ditch, a storm drain, or some other outlet.

Recommending a contractor to do corrective work is harder to do. It needs to be someone who understands these principles. It can be an excavator (I have worked with some who are savvy), a general contractor or a landscape contractor.

You may need to have a civil engineer or highly qualified home inspector survey your property and come up with recommendations and a plan of action. It is a good idea to have this person supervise the work as I have been involved in situations where I had written a very clear report with sketches and photos only to find out later that my instructions and design were not followed and needed corrections.