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Community and Q&A

Breaking thermal bridge between concrete porch and brick wall?

Paul Gorcey | Posted in Green Building Techniques on

I have a concrete-floor porch that replaced an original wood-floor porch. It butts up right against the double-brick wall of the house (built in 1905). The house is uninsulated, so I am insulating the brick wall with rigid foam board. While I’m at it, I am thinking it is a good idea to saw-cut a 1″ or 2″ slot of the concrete floor right along the base of the brick wall (in other words, the floor-wall joint) to get rid of the thermal bridge that might exist, then to backfill the slot with rigid foam. Does this sound like it would make a significant difference to heat conductivity? I’m in Toronto. Thanks.

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Replies

  1. Richard Beyer | | #1

    Sounds like a lot of work and a very bad idea. Brick breath's or it rots. Block those weep holes and there will be severe consequences to pay.

  2. GBA Editor
    Martin Holladay | | #2

    Paul,
    It sounds like you are adding rigid foam to the exterior side of your brick wall. Is that correct? (If so, that's the right way to do it.)

    What type of new cladding will you be installing on the exterior side of the new rigid foam?

    Assuming I have guessed correctly -- that you are adding a layer of rigid foam on the exterior side of your brick wall -- then it makes sense to cut a slot in the porch slab to interrupt the thermal bridge at that location.

    For more information on this topic, see Insulating Old Brick Buildings.

  3. Richard Beyer | | #3

    "Many older and historic homes were not designed with insulation, so it requires great care to select compatible insulating systems and materials. Older buildings, or those built before modern HVAC systems existed, were actually built to deal with the movement of air naturally through special design features. If your building was constructed before 1950, you need to give careful consideration before upgrading insulation. All systems – new and old – need to work in harmony."

    http://www.preservationnation.org/information-center/sustainable-communities/buildings/weatherization/insulation/

    http://epa.gov/region5/sustainable/pdf/Energy-advice-for-owners-of-older-homes.pdf

    http://energy.gov/sites/prod/files/2013/12/f5/expt_mtg_mass_masonry.pdf

    And, don't forget about termite prevention should you elect to follow Martin's advice... Regardless of the foam they are susceptible to termite damage.

    http://www.cbc.ca/news/canada/toronto/spray-on-insulation-a-highway-for-termites-experts-warn-1.1392079

    https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/coping-termites-and-carpenter-ants

  4. Paul Gorcey | | #4

    Thanks for the replies and the concerns. Just to clarify- the brick is exposed on the inside of the house, so it is able to breathe. I already covered the back wall of the house in this way- I also exposed brick on the inside. I attached 2x4 strapping to the outside wall surface, then rigid foam, then wood siding screwed through the foam into the 2x4. This leaves air channels between the brick and foam.

    I'm only insulating the front and back walls of the house (west and east walls) because these walls face the predominant wind directions. The north wall is tight to the neighbours, not a lot of exposure, so I'm leaving it for now, and the south wall is shared with the neighbouring semi-detached house.

    I don't think it will be a lot of work- the brick is only in the porch-covered area. I would need to saw-cut the porch for about 12 linear feet along the base of the brick wall.

  5. Paul Gorcey | | #5

    .

  6. Paul Gorcey | | #6

    Also - the rigid foam I installed on the back doesn't go all the way to the ground, but stops about 12: above. Hopefully termites wouldn't hop up a stone foundation looking for some fun further above.

  7. Richard Beyer | | #7

    Paul said; " I attached 2x4 strapping to the outside wall surface, then rigid foam, then wood siding screwed through the foam into the 2x4. This leaves air channels between the brick and foam."

    Do I understand you correctly? The air passage (1-1/2") is between the foam and the brick?
    Termites and carpenter ants will climb everything to get to food and shelter unless you install a termite shield and treat the soil. With ants, good luck stopping them. I suggest you read the links provided above because what you described, if I understand you correctly, sounds more like you created a wind shield rather than creating insulating properties.

  8. Peter L | | #8

    Just follow the recommendations and don't lose sleep over the termites or ants. Millions of people have EPS and the homes and insulation is perfectly fine. Rigid foam is not gloom and doom. Plus you live in Toronto and they don't have a termite issue like that of the Southeast USA or the Desert Southwest. Use borate treated foam and spray a termiticide every year around the home.

  9. Richard Beyer | | #9

    "TORONTO :) = TERMITES ;) = $$$$$$ DAMAGE("..... In this case $20,000 in damage!

    http://www.cbc.ca/news/canada/toronto/spray-on-insulation-a-highway-for-termites-experts-warn-1.1392079

    A wise tradesman once told me.... "It's never a problem as long as it's not your problem."

  10. GBA Editor
    Martin Holladay | | #10

    Paul,
    You wrote, "I attached 2x4 strapping to the outside wall surface, then rigid foam, then wood siding screwed through the foam into the 2x4. This leaves air channels between the brick and foam."

    This air channel between the bricks and the insulation caused Richard to worry about insects. I have a different worry: thermal performance.

    It certainly would have been better if you had installed your insulation tight to the bricks.

    If there is any movement of exterior air through the air channels you have created, then the value of your insulation is compromised. You might just as well have hung your insulation on a clothes line in your back yard.

    If you have managed to make the air space close to airtight -- by making sure that the bottoms and tops of the channels are tightly sealed to prevent any exterior air from entering or leaving the air space -- then the performance won't be seriously compromised. But it would have been far better to install the rigid foam directly against the bricks.

  11. Paul Gorcey | | #11

    Thanks again for the concerns. Re the 2 main ideas:

    1) if the cladding system doesn't come within 2 feet, or even 1 foot of the ground, leaving only brick, how are termites any more likely/inclined to access them than before, when there was only a brick wall? I know little about termites; can termites actually suss out wood or styrofoam?

    2) the cladding system is quite air-tight, at top, bottom, and around windows. I am fairly certain the air would be quite static. Also, I didn't want to put the foam directly against the brick because it would have been awkward to fasten 2x4 straps to a soft surface like foam, to ultimately anchor to the brick wall.

    Anyway, maybe I'll get proactive with termite treatment at the bottom of the wall, to be safe. Thanks all.

  12. Richard Beyer | | #12

    "I know little about termites; can termites actually suss out wood or styrofoam?"

    Read the links provided above. Your answers are there.

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