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Community and Q&A

Approach for adding insulation to existing concrete walls?

seekingsun54 | Posted in Energy Efficiency and Durability on

We just purchased a new (built in 1951) home and are working on some renovations before we move in. One major issue is the lack insulation in the entire house. The exterior walls are built of concrete block with full brick on the outside. Then looks like the interior plaster was put right up against the concrete block. The house used to have a flat tar roof, the previous owners added engineered trusses to create an attic space. Only insulation we have found is between the interior ceiling and old tar roof, nothing in the walls or the new attic. For the walls, the approach that has been suggested so far is to frame out the walls with 2x4s, add insulation and then drywall. Moving our switches and electric out as needed. Need some advice please!

1. Is this our “best” approach to increasing the efficiency of the walls? (We are adding attic insulation also and I know that will give us some huge efficiency gains.)
2. Is there any way to accomplish this other than with 2x4s to not eat up so much interior square footage?
3. What type of insulation would perform best?
4. I found a few articles that had concerns about the effect of adding interior insulation to the exterior masonry product (freeze/thaw, etc.). Would that be a concern here?

We are in zone 4A/5A (on the border).
Thank you so much! We are overwhelmed with everything that needs to happen in this house! It is planned to be our forever house so we want to make sure we get the most possible efficiency long term.

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  1. Kevin_in_Denver | | #1

    If the brick is deteriorating or painted, you might consider going with "outsulation" attached to the outside of the house. Staggered layers of taped foam may give better airsealing, you don't lose any floorspace, and you get the benefit of the thermal mass of the existing wall.

  2. GBA Editor
    Martin Holladay | | #2

    If there is any way you can follow Kevin's suggestion of installing foam insulation on the exterior side of your brick walls, that is always the best approach to insulating a building with uninsulated masonry walls. The easiest way to do this is with EIFS (synthetic stucco over rigid foam). If you decide to go this route, you should call up some EIFS contractors to get estimates.

    If you really want to keep your brick exterior, you'll need to install interior wall insulation -- either closed-cell spray foam or rigid foam installed on the CMUs. For a variety of reasons, including possible problems with inward solar vapor drive, I don't recommend that you use air-permeable insulation like fiberglass or cellulose.

  3. seekingsun54 | | #3

    Thank you for the feedback! The brick is in great condition and we do not wish to cover it. Sounds like we are going with internal insulation solution. Thank you for the advice on the type of insulation.

    We do however have a smaller guest house on the property of CMU which does not have any other exterior materials. So we can go the external rigid foam route for that building.

  4. user-1061844 | | #4

    I would first check that the house is managing rain well - has good gutters, lintels, sill that direct water away from the wall. Then check for any spots that get soaked during a rain storm. If the brick stays dry, and is relatively hard/non-absorbing (Probably since there is CMU on the inside, so it is not 125yr old brick). It is probably pretty save to insulate on the inside. At, we like to stay away from foam for various reasons (sustainablility, off gassing, shrinkage) - avoiding foam will also allow the wall to dry inwards if needed, but does require a smart vapor retarder like the INTELLOmembrane that we supply. Please see our blogpost the possibilities and dangers of interior insulation in masonry buildings for more details, tips to get make the envelope airtight which gets the most out of any insulation (also around your floor beams) and let me know if you have any additional questions (and don't forget to insulate your roof..)

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