Crawlspace vents should be kept closed

Q.  In a recent column you recommend closing the vent openings in a crawl space. I thought in the past you recommended to keep the vents open all year round. Ventilation is needed in the crawl space for health reasons. So what is the correct procedure: Close the crawl space foundation vent openings or leave them open all year round?

A.  If you read that crawlspace vents should remain open, it was not in one of my columns or blog posts. Ever since the 1970s I have recommended that crawlspaces not be vented, if the soil is thoroughly covered with plastic or other vapor retarder.

During that time, national research demonstrated that vented crawlspaces had far more problems than non-vented ones. But, again, the soil must be completely covered with a vapor retarder.

Wasps invade crawl space

Q.    We have a house with a cement tile roof and a vinyl type stucco siding. Wasps seem to be attracted to the siding and yellow jackets recently entered our crawl space through a small hole behind a copper sheathing.   Recently  we’ve had several enter our living space and we were stung while we slept.

We taped all possible entrances such as light fixtures and fans and have now noticed several in our basement. Initially we sprayed with RAID but could not reach the hive from any direction and it left stains on the bottom of the plywood-stucco eaves. We then placed a strong vacuum in front of the hole and have now siphoned off thousands but there is still activity. Will those remaining bees continue to hunt for a means of escape if I plug the hole? Will steel wool work best as a plug? What else can we do?

Wasp Trap
Raid brand wasp trap

A.    In the fall, the yellow jacket queen comes out of the nest to mate before hiding for the winter, and the workers die. This is the time to set a RAID pheromone trap that attracts the males, thus interrupting the mating cycle. You should be able to find these traps in garden-supply stores and some supermarkets.

Once cold weather has set in, and after you have either vacuumed the rest of the nest or had a pest-management professional deal with the hidden nest, seal the hole they use to get in and out with an appropriate material. If the hole is small, caulking may be the best way to do so. Use a polyurethane caulk of a color closest to the synthetic stucco or copper flashing.

Considering the severity of the problem, I would advise you to hire an independent, locally-owned professional pest-management firm.

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.

Pipes freeze after furnace is moved from crawl space

Q.  My wife and I recently bought a small ranch that had an old, inefficient furnace in the crawl space. During the fall, we disconnected the old furnace and decided to install a new furnace in our attic space and run new ductwork. Things seemed to be fine until we had a sustained cold and windy period which froze our water pipes. We did not take into consideration that the old furnace in the crawl space was emanating enough heat to warm the space and keep the pipes from freezing.

I purchased an electric heat tape and fiberglass insulation, and applied it to the area that I believe to be most susceptible to the freezing (along the foundation wall running almost the full length of the house). We again went through a cold spell and the pipes froze, despite the heat tape.

I have received many recommendations for fixing the problem ranging from heating the space to re-piping with technology that has the heating element within the pipe. Any suggestions you may provide will be appreciated.

A.    It was a mistake to put the new furnace in the attic. The heat it generates will cause snow on the roof to melt, thus causing ice dams to build up at the eaves. This can result in leakage inside the walls, wet attic insulation and damage to wall and ceiling finishes. There is also a loss of efficiency as the furnace is in a cold space that is presumably ventilated; any benefit from the furnace’s stand-by losses is lost. If the furnace had been left in the crawl space, its stand-by losses would warm the crawl space, keep the pipes from freezing, and warm the first floor.

Since it is unlikely that you will go to the expense of returning the furnace to the crawl space, and if the insulating you have done is not as described below, I suggest that your first step be to seal any cracks admitting cold air anywhere around the foundation; this will keep the wind out. You should caulk them.

If there are any vents in the foundation, please close them and place insulation over them. If you haven’t done so, this is how the crawl space should be insulated: put R-19 fiberglass between the band joists with a vapor retarder facing inside the crawl space; insulate the walls down to two feet below grade with either fiberglass or rigid insulation.

It is not safe to go below the two-foot level as it could result in walls cracking under the influence of deeper-penetrating frost. This should prevent further freezing of the pipes that are surely just under the first floor joists, as the earth’s warmth and the heat loss from the first floor should keep them above the freezing point.

You should also insulate the water pipes with neoprene insulation you can buy in hardware or building supply stores; they are easy to install. However, if you have already insulated as described above, and insulated the pipes, you may need to provide a modicum of heat. I know of old stone cellars in which pipes used to freeze until a simple 100 watt light bulb was kept on during cold weather and proved to be sufficient to keep the pipes from freezing.

Water condenses in crawl space

Q.    I have a split-level with a crawl space under the main floor of the house. The crawl space has a cement floor, with rigid pink insulation foam board covering the cinderblock walls.

There is R-19 in the rafters with the paper facing the floor of the room above the crawl space and three 6-inch x 9-inch screened openings to the outside for venting. Every year the rafters and the insulation get so damp that water droplets form on them. Water actually drips off of the gas pipes, water lines and insulation in the crawl space.

I put a large fan in the crawl space and after a few days it seems to dry everything out. Why does this happen and what can I do to prevent it from happening again?

A.    The outdoor, humid air of summer gets into your crawl space that is kept cool by dint of its being in contact with deeper, cooler soil. Some building codes still erroneously specify crawl space ventilation, although it is well-documented that in most climates — and particularly in warmer, more humid areas such as the southeast — this ventilation has been responsible for major structural-rot problems.

Newer science recommends not ventilating crawl spaces as long as the floor is protected from soil moisture by a sheet of 6-mil plastic or a concrete slab. Since your crawl space has a concrete floor, there is no need for additional measures. Close all vents and see if it solves the problem. You may need to put a dehumidifier in the crawl space until the moisture level is greatly reduced.

Installing radiant heat in crawl space

Q.    I live in a 25- to 30-year-old, 1600-square-foot ranch.  I have been trying to improve the energy efficiency over the two years that I have owned it, including adding insulation and replacing windows.

One room is the width of the 2-car garage, located at the back of the garage and about 10 feet deep. It has just a crawl space under it and is on a different zone on the forced hot-water baseboard heat. I am thinking of converting to radiant floor heat as everything is exposed in the cellar. Can I do that in the cold crawl space? How would I insulate and protect it in there?

A.    I don’t see any reason why you can’t convert to radiant heat in the crawl space. If it is properly installed by experienced contractors, it should work fine. But select the contractor carefully. I have seen an installation where the contractor used nails and staples to fasten the radiant tubing in spite of the fact that the manufacturer expressly warned against it. The tubing was drooping and leaks were not far behind.

The tubing needs to be straight, held about 1-inch below the subfloor by approved fasteners that are spaced according to the instructions to avoid sagging. Reflective pans are installed below the tubing, and the rest of the floor joists’ depth is filled with fiberglass of the recommended R-factor, considering the make-up of the floor above. The tubing should also be installed so that it avoids as many concealed couplings and joints as possible. This is not a job for amateurs.

Avoid organic mulch around foundation

Q.    In a recent post you said it is best not to put mulch next to foundations because it attracts bugs. What about cedar mulch? I’ve been under the impression cedar mulch deters insects and is OK to use next to the foundation.

A.    Any organic mulch will hold moisture and eventually decompose. This is an ideal breeding ground for all kinds of bugs including earwigs. It is also best not to have any material that holds moisture against the foundation as it can lead to basement or crawl space water problems.

I have always recommended sloping the ground away from the foundation and planting grass as the vegetation of preference. Grass has deep roots and continually draws moisture out of the soil which is what you want. However, if you want to use a mulch, the best kind is the recently available rubber mulch made from shredded tires. It won’t hold moisture or rot, and it is not unattractive.

Will humidity in a shore area damage laminate flooring?

Q.    We are having a pre-fab house built in a shore community. The houses are built around a series of lagoons. The house will be built on 4-foot pilings. My husband would like to install Pergo laminate flooring throughout the 2-story house. A floor dealer told us that the humidity from the shore area may cause the floor to buckle or lift. We had been shopping around and had not heard that before.

My husband called the Pergo company and was told to put a 6-mil vapor barrier underneath the crawl space before installing the floor. Would you please advise on this?

A.    If your house is built on 4-foot pilings and the area underneath the house is kept open, I don’t see how the flooring can be affected by the humidity. There should be enough air circulation. In that case, putting down a vapor retarder on the open ground is worthless. However, you mention a crawl space. Does this mean that there will be a skirting around the perimeter of the house? If so, you should definitely cover the crawl space with 6-mil plastic and do so thoroughly.

I also assume that the floor of the house will have some insulation. If the area under the house will remain open, there needs to be some fabric covering stapled to the bottom of the floor joists to protect the insulation from animals. Mobile homes have such fabric called “road fabric”. A housewrap will also do. I suggest that even if the house will have skirting around, housewrap should be stapled to the bottom of the joists.
It would be advisable to check with one or more other installers of Pergo flooring and get their opinion. They are familiar with the local conditions and may have had bad experiences which they are not anxious to see repeated. Or perhaps, the one you spoke with is extra conservative.