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Best approach to deep energy retrofit the stud bays in a brick home?

W. Timothy Ward | Posted in Energy Efficiency and Durability on

I have a three-story brick home in climate zone 5 with interior plaster walls on both wood and metal lathe-at least 2 inch thick in many areas based on prior renovation of a bedroom. Home was built in 1920 without stud bay insulation.

I am considering retrofitting the stud bays with dense packed cellulose. Is there a general preference to do this project from the exterior by drilling through the brick and plywood sheathing or is it better to do internally by drilling through the plaster and lathe? What are the pros and cons of the two approaches ? Internally would seem to require the services of the cellulose installer, drywall crew, and painters while externally would require a brick mason crew and cellulose installer. Is it typical for an insulation company to offer total job service from either the interior or exterior or does one always have to piece meal the job?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Timothy,
    Insulating an older brick building with cellulose is risky, and is usually not recommended. To read about all of the risk factors that need to be considered before settling on an insulation strategy for an older brick building, I suggest that you read this article: Insulating Old Brick Buildings.

  2. W. Timothy Ward | | #2

    Martin
    As always your response is most helpful. I read the article and the comments. It appears that if the brick is non structural (one or two layers thick) and in my climate zone (Pittsburgh) then the drawbacks are felt to be minimal. I understand that there is always judgement involved but is the practice generally felt to be safe and acceptable from your standpoint for non structural brick in zone 5? There are many houses that fall into this category where the homeowner would like to improve the efficiency of the walls without covering them up with EIFS

  3. Expert Member
    Dana Dorsett | | #3

    Take a hard look at how much eave & rake overhang you have- if it's less than 1" of overhang for ever foot of height above grade you have the potential for rain-wetting of the cellulose through the brick on the lower part of the wall during rain events as the brick gets saturated. More overhang is of course better, but anything less than 1" per foot would be imprudent. For a 3- story that's going to be some overhang!

    Sometimes it's possible to insulate much of the wall from the attic & basement without drilling either brick or the interior side. On balloon framed structures you may need to block joist bays between floors with a feet-bag inserted into hole drilled in the ceiling then dense-packed with cellulose first, or you'll end up pumping 3-5x the volume of cellulose into the house, filling up the the stud bays.

    If it's only ~4" of cellulose depth on the walls broken by studs it's not exactly what most in the industry would call a "deep energy retrofit", but it might bring the U-factor of the wall to nearly code-min for new construction. IRC 2012 code min for zone 5 is 2x4/R13 + R5 c.i., or 2x6/R20, which is about R14-R15 whole-wall. Full-dimension 2x4s balloon framed 16" o.c. might have a framing fraction of as low as 15% (in our dreams- 20% is more likely), which would yield a whole-wall R of about R12. That's a huge improvement over the ~R3 or whatever it's current performance, but "deep energy retrofit" usually refers only to something 2x code-min or better on all sub-assemblies. (A DER I was involved with a couple years ago on a 3-story 1890s building in zone 5 hit around R40-ish whole-wall, which took about 4" of exterior rigid foam over the plank-sheathed balloon framed structure.)

    A 2" shot of closed cell spray foam on the exterior brick as insulation and with 1/4-1/2" of rainscreen gap under some fiber cement wood siding would bring you close to 2x code-min for wall performance. Closed cell foam is it's own weather resistant barrier, so it simplifies it a bit. Some analysis of the condition of the ties between the studwall and brick might allow you to fasten the furring for the siding to the brick-only, not all the way through to the studs.

  4. W. Timothy Ward | | #4

    Thanks Dana, very helpful

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