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Thread: Insulating Brick home in OK?

  1. #1
    DIY Junior Member Chellayh's Avatar
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    Default Insulating Brick home in OK?

    We recently bought a 1952 home in Tulsa, OK with brick cladding, plywood (I think) sheathing with drywall & no insulation in the exterior walls. We are thinking about using Retrofoam www.retrofoam.com - but their normal procedure with brick cladding is to foam the air gap between the brick and sheathing. I am concerned about the effects of filling the air gap, esp concerning moisture effects on the brick, sheathing and drywall. DO NOT want to cause any mold problems or bigger messes (rotting sheathing, crumbling brick)!

    They can go in from the inside & fill the space between the studs. Not my favorite solution, as we just paid to have the whole inside painted. I am concerned about moisture problems with this also, because as I understand it, Retrofoam acts as a vapor barrier, and I believe in my climate, vapor barriers should not be placed on the inside. But unsure about this, because of the foam sealing both at the back of the drywall AND the inside of the sheathing. The differences in the foam insulation from standard insulation has me confused on the vapor barrier thing.

    If the retrofoam won't work, what is my best option without taking out the drywall? I will reluctantly patch interior holes if needed. The ideal solution would go in through the mortar joints, but I am starting to think that may not work.

    Thanks!
    Cheryl

  2. #2
    In the trades Dana's Avatar
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    How big is the gap between the brick and sheathing? If it's 2" or more filling the gap would give you a reasonable R value even without filling the stud bays and would be relatively safe for the sheathing. If it's an inch or less, the insulating value is miniscule, and there is increased moisture risk to the sheathing.

    The space between the masonry and the sheathing is necessary to protect the sheathing from moisture drives coming from the exterior. It works best if it's vented to the exterior at both top and bottom. The vents don't need to be huge to work, weep holes every 3- bricks or so at the bottom and corresponding slots cut into the vertical mortar between bricks every few bricks on the top layer allows enough convection to purge high moisture conditions. These conditions typically happen in summer. Brick is porous and will absorb & store a good amount of rain & dew. When dew or rain-wetted brick gets heated in the sun the moisture is driven off rapidly resulting in VERY high humidity levels for a few hours at a time. But as long as the sun-heated very humid air in the cavity space is allowed to convect to the outside pulling in drier outdoor air, very little of that moisture ends up in the sheathing.

    When you fill the gap with non-expanding injection foam there is no convective purging taking place, but the foam itself is modestly vapor retardent (about 15 perms @ 1", about 8 perms @ 2"). The 15# felt commonly used on the sheathing in those cavities is more vapor retardent than the non-expanding injection foam, but at 2" or more the foam is at least helping, whereas at 1" or less it's permeance is too high to have any protective aspect at all.

    In a Tulsa climate the resulting higher average moisture content in the poses absolutely no risk to the brick, but in much colder places such as Winnepeg or Fargo, closing up the gap with foam would risk freeze/thaw spalling on the exterior face of the brick.

    The other significant question to answer before filling the gap with foam is how the flashing on the windows & doors are set up to drain. If (as is common) the flashing is using the felt on the exterior of the sheathing as the drain plane, filling the gap with foam could result in higher moisture content in the window & door framing with rot potential, since bulk-water incursions would take an order of magnitude longer to dry.

    In general the safest thing to do is to insulate the stud-bays, and leave the masonry cavity alone. (If the cavity is not already vented, drilling in vents & weep holes on the top & bottom courses is worth it.)

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    DIY Junior Member Chellayh's Avatar
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    Thanks, Dana! From reading other posts, I knew I could count on you for an answer!

    I think it's probably only 1". Need to drill to find out tho. It has no weep holes top or bottom. The bottom brick goes below the soil line - common here in this age of houses. We have talked about drilling weep holes. Not sure about the window drainage, but we are replacing them with high quality vinyl windows, but as inserts, not full replacements, so the wood trim will remain untouched.

    Would it be better to use foam on the inside or try to find a dense packed cellulose installer? I was a little concerned with the foam about a vapor retardant material being on the inside, but wasn't sure.

  4. #4
    In the trades Dana's Avatar
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    The non-expanding injection foam at 3.5" is about as vapor-open than 2 coats of standard latex paint, so it's not like would be blocking the sheathing from having drying path toward the interior entirely. In a 2x4 cavity it's vapor permeance is between that of open-cell spray polyurethane foam (SPF) and closed cell SPF, but much closer to open-cell.

    Injection foam is more air-retardent to infiltration flows than dense-packed cellulose, but not by a huge amount. Unlike expanding SPF, injection foam isn't flexible and doesn't create a glue-like bond. Seasonal changes in humidity can leave micro-gaps between the foam where it meets the studs, since the studs change dimension with moisture content. In practice this is not a big deal, but it's the reason non-expanding injection-foam doesn't air-seal as well as spray polyurethane does.

    For even money I'd go with cellulose (mostly for environmental impact of production reasons), but if injection foam is cheaper go for it- it's pretty good stuff overall, and WAY superior in this application to low-density fiber.

    If the house was built in 1952 it's very likely to have had at least some flashing. If it was flashed to re-direct toward the exterior it was most likely metal flashing, and you'd likely be able to see where it comes out flush with the masonry just below the exterior sill. But it's probably more common to have been a heavy felt flashing directed to the felt over the sheathing in the cavity. It might be hard to figure it out without some major disassembly, but if you vent the cavity to the exterior top & bottom (or if not bottom, 6-8" above grade) it won't much matter- the cavity will then purge accumulated moisture to the exterior.

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