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Q. We have a 25 year old house with an unfinished basement. The ceiling is insulated with batt insulation with the paper side to the ceiling. There are also large sheets of plastic that have covered the insulation (stapled to the floor joists). Over the years mice and snakes have gotten in and left their excrement on the plastic and surely in the insulation. We plan to remove the insulation, but am wondering the wisest way to re-insulate. I read somewhere (This Old House?) that one only needs to insulate the perimeter. We do have ac/heat ducts in the basement, but it is still quite nippy in the winter. Of course, once the insulation is gone we will try to find the holes where the animals are getting in. We have caulked and used canned foam insulation to fill any obvious holes but there is still a hole somewhere! Would greatly appreciated your insight.
A. The insulation may have been installed properly with the foil or kraft paper side to the living area of the structure but whoever stapled that plastic moisture barrier directly onto the joists and under the insulation may have had their hearts in the right place but not their head. The moisture barrier located where it is can, if conditions are right, become a condensation plane within the joist spaces and create wood rot. Back in the 1970s when folks started to retrofit insulation into older homes they sometimes did just what was done at your house to houses on crawl spaces that sometimes got wet. The moisture migrated upward and was trapped in the joist bays and held by insulation and the occupants didn’t know what was going on until the floors got spongy underfoot and by then it was too late.
The atmosphere in the enclosed space is vacationland for mice, snakes and I’m sure several species of insects and they have been there for a very long time. When you go to remove this material you need to take special care to protect yourself and the rest of the house from the contaminants trapped in that space that removing the barrier and insulation will liberate. Get yourself a set of those Tyvek coveralls, gloves, eye protection-- the type that fits tight to your face- and most importantly a quality particulate respirator-- not one of those useless little white things. Don’t go cheap on this safety equipment because the person you are protecting is you and the dust you’re going to kick up doing this is hazardous. The next thing to do is to get at least one or more inexpensive box fans and place them in open windows and blowing out turn them on high. Open windows on the other side of the basement and one upstairs. This will move air from the basement to the exterior carrying a great deal of the airborne contaminants with it. After you’ve taken all the insulation down and placed in large plastic bags sealed for disposal you’ll want to go over everything yet again with a shop vac while still leaving the fans on. You’ll want to change the filters in your air system, too. You probably have a heat pump so when your house was built the unfinished basement was not considered a conditioned space and for the calculus of the heating and cooling system was outside of the building’s thermal envelope and had to be insulated that way. If you have ducts down there I recommend cutting a register or two into them to deliver some heating and cooling to the space if for nothing else but for dehumidification. If your plan is to finish off the basement then studding up a wall on the inside of the exterior foundation walls and insulating those walls is the way to go. Then you can run wiring for outlets, cable etc before placing a wall finish over that. The one unanticipated benefit of insulation between the joists was sound deadening. If the plan is to use the basement space for a playroom or home theater then re-installing even just four inches of fiberglass insulation would restore that feature and wouldn’t affect what you do on the sidewalls. Good luck sealing the exterior one hundred percent against invading critters. They have an uncanny way of getting in. Reducing their number is achievable but elimination almost impossible.*end