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:
- 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?
- 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.