+ Reply to Thread
Results 1 to 5 of 5
  1. #1
    Join Date
    May 2012
    Posts
    1

    Question 30" stone walls - opinions on insulating on interior

    My daughter just bought a 150 yr old farm house with 30" fieldstone walls. They want to redo on room (remove lath and plaster and drywall it). They feel that they should insulate before putting up the drywall. I feel this will defeat the "U" factor which provides a heat/ cold sink. The house is in Wisconsin and we get 0 degree in winter and 90 degrees in summer.

    Any advice on this project??

  2. #2
    Join Date
    May 2009
    Location
    Elyria, Oh.
    Posts
    245

    Default Re: 30" stone walls - opinions on insulating on interior

    Using the standard insulation value for stone or concrete of
    R-0.08 for each inch of stone or concrete you would end up with an insulation value of about R-2.4 for your 30 inches of stone. Masonry has one of the lowest R values per inch of any material.
    Even 1 inch of a standard insulation board that you can pick up any any big box store or lumberyard would at least triple the R value by itself. Most basement in the north have been insulated by adding insulation boards on the outside for decades because it is well known that masonry, stone, etc is a poor insulator.

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,683

    Default Re: 30" stone walls - opinions on insulating on interior

    Stone is a giant heat sink, it will suck the heat right out of the room. If you want it for a thermal mass, you must insulate it from the outside, but even then if it has ground contact, you wont heat much above the ground temperature.

    Let her insulate it. The trick is going to be venting the insulation. Try to get some outside airflow through the insulation if at all possible, otherwise spray a closed cell foam right on the rocks.

  4. #4
    Join Date
    May 2011
    Posts
    251

    Default Re: 30" stone walls - opinions on insulating on interior

    I think we're underestimating the thermal mass. IF you have enough thermal mass, you only need to be concerned with average daily temperatures. So in winter that means you can size a HVAC system in WI similar to one in Seattle. A northern home with stone won't need AC< just a whole house dehumidifier with ventilation.

    However, even insulating it form the inside you'll still have the similar affect of the thermal mass because if you for example add 3" of spray foam between 2x4's, you get an R-value of 15-18, but the delta T will be based more on the average daily temperature plus any solar heat gain. The BTU's gained or lost are based on the stone temperature and divided by the R value of the foam.

    I get some of this sme effect even with just stucco walls and plaster inside my house. I basically have 1" of light concrete providing thermal mass wiht two 1/2" pieces of beadboard for insulation. People are shocked at how low my ulity bills are for a oild house this size.

    What you don't want is air movement between the insulation and the stone. You will get condensation and mold... guaranteed. Either keep it sealed or let it breathe. That's why spray foam is the best choice IMO.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  5. #5
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,683

    Default Re: 30" stone walls - opinions on insulating on interior

    "What you don't want is air movement between the insulation and the stone. You will get condensation and mold... guaranteed. Either keep it sealed or let it breathe. That's why spray foam is the best choice IMO."

    What you don't want is INSIDE airflow against the stone. I don't know how you would do it, but if you have OUTSIDE airflow between the interior insulation and the stone, it will keep the stone dry. But short of finding a way to get outside air into the cavity, I agree with the spray closed cell foam.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •