INSULATING STONE WALLS OF A HOUSE

QUESTION FROM JOHN:  

Can I pour insulation into my walls from the enterior directly against my exterior stone walls. My house is 140 years old and is constructed of 18  inch thick stone walls. The only option is to insulate from the inside.

My thoughts were to drill holes and blow in from the inside. The stone wall does not have a vapor barrier so the insulation would drop between the slats and the stone. Is this a good option?

ANSWER FROM THE INSULATION DOCTOR:

Thank you for your inquiry, Tim. Sorry I took so long to respond but because of the weather lately I have been over-whelmed with questions.

My first suggestion would be to check and see if you have insulation installed in what is commonly referred to as the "bond plate". The bond plate is the space between the rafters at the end of the joists that sits on top of your basement block walls. It is recommended that you have a minimum of R-19 unfaced blanket insulation, cut to size, in each rafter bond space cavity. The insulation should be placed down the back of the bond, facing the inside, and then come over the top of the block to the end of the block so that the insulation forms an "L". This should be done in every bond cavity in your basement.

Rather than insulating the floor between the basement and the main floor, I would recommend that you first try minimally heating the basement area. Because heat rises, this will cause the heat that you use to heat the basement area to rise up and thru the floor and be helpful in heating the main floor.

If that does not help solve the problem I would recommend insulating the walls of the basement. The reason I usually do not recommend insulating the ceiling between the basement and the main floor is because it will isolate the basement and the floors will actually become cooler.


Regarding using styrofoam sheets on the basement walls, you would normally have to use at least 3/4" furring strips between the sheets in case you ever decide to drywall it. It is against the BOCA construction code to leave any Styrofoam product uncovered. It is also a fire hazard. Foam will burn vertically. The other problem with Styrofoam is that it has a low R-factor density. For example, normal density on closed-cell (Owens or Dupont) 1" foam is R-5. If you were to stud the walls out and install 3-1/2" R-13 blanket your cost would be approximately the same due to the fact that foam is very expensive.

You would also have to cover the R-13 blanket insulation to conform to the fire code. There is one other application that you could employ and that is to drape a commercial grade fire-proof (FSK-25) insulation down the walls. This product does not have to be covered because of the covering is on it but, again, this is a commercial product, expensive and hard to find. Hope this helps you.

Bruce Jones
 The Insulation Doctor

Additional Info:
Hello Tim, Good luck on your project this weekend. I was looking for the FSK-25 insulation I mentioned to you for the walls of your basement since it has been very hard to find in the past. I discovered they sell it at Menards if there is one near you.