GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

How do I “best” insulate my 8″ brick exterior wall 1 1/2″ air gap wall?

GBA Editor | Posted in Energy Efficiency and Durability on

I am in trhe process of renovating a home built in the early 50’s. The exterior is 8″thick red brick, looks as though they coated the interior with a painted on mortar slurry of some sort. then attatched 1 1/2″ furring strips followed by rock board 1″ thick followed, by 3/4″ plaster. The bricks are the load bearing wall that the rafters sit on. Anyway, with basiclly no “R” value to speak of, I removed the plaster and furring strips on the inside the home on all exteriorfacing walls and was planning on building 2″x4″ interior walls with insulation and then drywall. as I search the web I found this site and am at somewhat of a loss as to what best to do to complete it. I do intentd to install a hybird heatpump/ propane furnace A/C system and I live in central Ohio
Would it be best to spray foam the walls 2″ thick then fiberglass bats then drywall, or could I put tyvec on the brick for a vapor / air infiltration inhibitor, then fiberglas then drywall. I am not saying cost is no object but I would like a safe mold free wall system when finished.
Thanks for listening. John Walter

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Insulating a brick wall makes the bricks colder, and therefore wetter. In some cases, insulating a brick wall makes the wall more vulnerable to freeze/thaw damage.

    It takes an experienced building science consultant to assess the risk factors in such cases. Do roof overhangs protect the walls from rain? How cold does it get during the winter? Are the bricks and mortar very absorptive or only somewhat absorptive?

    There is no simple answer to your question.

    By the way, Tyvek is not a "vapor inhibitor." Tyvek is permeable to water vapor.

    You should use the search function of the GBA Web site to research this issue. I suggest you use the search terms "brick insulate."

    You might want to check out these pages:

    In addition, I strongly advise you to read "Insulating Residential Masonry Buildings In Cold Climates" by Chris Benedict (in the the current edition of Home Energy magazine, March / April 2010).

  2. Anonymous | | #2

    I did read the links you gave to me appreciate the advise. To further explain the home, It is a single story with a good 14" overhang on all sides, the brick is smooth tight and according to the neighbor , has been sealed every 3 years for many years. There are no cracks noticable and all the window sills are concrete and tight ,no major weep marks. In our rea of Ohio it seldom gets below Zero,and the home sets in an area protected from the northern winds by hilly wooded areas.
    By what I have read so far it seems feasable to sray foam the brick two inches then set the 2x4 walls and 3" of fiberglass batts then drywall. According to the "Foamit green" site Flash & Batt is a very popular way to insulate walls and buildings. It's a great way to get the benefits of spray foam and save money on insulation at the same time. You use 1 or more inches of Foam it Green and then fill the rest of the cavity with fiberglass or another form of insulation. You get the high r-value and tight building envelope from Foam it Green. The fiberglass adds some r-value without having its performance destroyed by air flowing through it. They recomend 2" of Foam and 1 1/2 to 3" of insulation. According to them
    •2x4 walls = 3.5 inches of space.
    2 inches of Foam it Green = R-14, 1.5 inches fiberglass = R-5 The Dew Point will be in Foam it Green and thus minimize moisture issues.
    •2x6 walls = 5.5 inches of space.
    2 inches Foam it Green = R-14, 3.5 inches fiberglass = R-12.25 The Dew Point will be in Foam it Green and thus minimize moisture issues "
    This seems plausible to me , however I am not an expert, but it does address the issues I thought You raised.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |