Q: I have an older home with a stone foundation. I would like to insulate the walls and was wondering what you would recommend. They are mostly dry but get a little damp in the spring. I do run a dehumidifier set at 60 percent humidity. Also, there are bricks mortised in between the floor joists so I cannot insulate there.
Thanks for any suggestions.
A: I believe what you are describing is a cellar or basement. While I would always suggest insulating the exterior side of the walls below grade, sometimes it is not feasible.
In your case, dealing with the moisture on the walls is a critical step before insulating. You will need a system that will allow the moisture or water that transfers through the foundation wall to be directed to a drainage system and then removed.
For a stone foundation I would suggest a layer of heavy plastic to create a moisture barrier. The moisture barrier should be sealed to the top of the foundation wall, loosely laid over the stone foundation walls and extended to a drainage system at the base of the foundation walls. The drainage system at the base of the walls will need to be directed to a covered sump pit with a pump that directs water to the exterior and away from the foundation.
Once the system is in place to deal with the moisture, closed-cell expanding spray foam can be sprayed directly over the plastic moisture barrier. Check with your local code officials to determine the minimum R-value required for current foundation insulation. In my area an R-10 is the minimum insulation value. Also keep in mind that the foam cannot be left exposed. In most situations exposed foam is a fire hazard. If you do not plan on covering the foam with a finished wall system, you can use a spray foam that has fire retardant built in.
You can always leave the foundation wall uninsulated. The cost to properly insulate your stone foundation wall versus the cost in energy savings after insulating may not be worth the investment. Consider consulting a certified energy rater in your area to determine the estimated return on the investment. I have found that sealing up air leaks in all areas of the home can provide better efficiency and comfort and have a greater impact than just insulating the foundation walls. The floor joists at the brick walls can be caulked or foamed to restrict air infiltration.
———
C. Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 268, Evansville, Ind. 47702.
About the Author
