An existing basement wall is not insulated on either side. Humidity inside is causing significant sweating on the cold wall in the winter months. Outside, the top 4 feet of wall are exposed above the ground. I am less interested in insulating for energy savings and more interested in avoiding the condensation problem as the basement space is actually a garage. Will I solve the condensation problem by insulating only the outside wall to a depth of about 2 feet below grade. If not, then what is the best way to insulate the inside with a proper vapour barrier to isolate the humid air from the cold wall?
Should I insulate the exterior foundation wall above grade or insulate the interior basement wall
condensationfoundationinsulation
Related Solutions
Insulation is always installed as such:
Warm side | Vapor/ Moisture barrier | Insulation | Cold side
You ONLY want a moisture barrier between the warm side and the insulation, because warm air holds onto more moisture than cold air, and when warm air meets cold (air, wall, whatever), the air has to let go of that moisture as it cools, forming condensation. The moisture barrier prevents that moist air from getting into the insulation where cold and warm meet.
If you put insulation on the wrong side of your barrier, the moisture will form in the insulation, and as Shirlock said, if you create TWO layers of barrier, you create a potential moisture trap.
There is a rigid polyisocyanurate foam core insulation, often sold under the brand name Super Tuff from Dow that has a higher R value than XPS. It is R-13 in 2 inch panels and is higher if you trap a small air barrier behind it (around R-15).
The foam has a foil vapor barrier on the back.
You could
- mount this on the existing furring foil side out, using glue and screws
- seal the edges with foil tape
- reinstall paneling with glue and screws throught the foam, into the existing furring.
HOWEVER: The paneling could hold itself up when mounted this way, and you could mount lighweight things, such as pictures. The walls would NOT be suitable for mounting shelves, fixtures, heavy mirrors, etc. You would need to take care and inform any subsequent owner that the walls were not intended for bearing any signifciant weight!
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Best Answer
Insulation slows the loss of heat, it will not raise the temp of the wall above the dew point unless there is a source of heat inside. (Heater, leakage from another source, or a day/night average temp above the dewpoint.
You may be best looking for a way to lower the humidity in the space. Removing standing or leaking water, finding vapor leakage from the conditioned space or other sources of moisture (clothes dryer vented into the space). You may want to contact a basement specialist contractor. Concrete is porous, and if the wall were not sealed with a watertight membrane before backfilling moisture can be leaking through the walls. If you do not wish to heat the space, adding ventilation to get the wet air out will help.
Once that is done you can think about insulating. The easiest, though expensive, solution is to spray cold cell polyurethane spray foam on the wall. This will act as a vapor barrier and insulation, and it has no air space behind it for condensation. Second best is solid foam board insulation outside, from top to bottom of the wall (even underground).