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How to insulate brick over cinder block?

jcresko | Posted in Energy, Heating & Insulation on March 19, 2008 06:34am

Guys,

I’ve been reading FH for a decade, but totally new to the website.

I have a 1950-ish ranch house constructed of brick over cinder block that I’m getting ready to put a 2nd floor on. The first floor will remain largely untouched. Does anyone have advice on insulating between the brick and block (about a 1 inch space)?

Once the current roof comes off, I’ll have some access to that space from the top. However there are several rows of bricks that stretch the gap to the cinder block, so blowing in foam will only reach down about 3-4 feet. To insulate the rest of the way I would need to have access from the brick side (holes through mortar) for access.

Is it worth it? Problems closing of this air gap? Closed cell or open cell? Any other suggestions (no, I won’t build interior stud walls, too late for that……)

Thanks!

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Replies

  1. User avater
    FatRoman | Mar 19, 2008 02:09pm | #1

    Welcome to BT.

    I don't have an answer to your question, but I've got a house constructed in the same fashion and would be interested in the same idea. So this will help bump your message to the top of the queue.

    And since you'll get information better tailored to your situation, make sure you fill out your profile. Your insulation needs in Florida are a little different than they would be in Ottawa.

    Best,
    Steve

    'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb
  2. User avater
    McDesign | Mar 19, 2008 02:15pm | #2

    I think you need that 1" space as a drainage plane - brick's pretty porous.

    Forrest

  3. Piffin | Mar 19, 2008 05:03pm | #3

    That space is what we cal a drainage plane. It is there so that water that blows in through the brick can migrate to the bottom and drain out the weep holes.

    Filling it with insulation will cause more problems than it solves.

    The two ways to insulate this wall are to use pourable perlite or soft foam in the block cavities, or to insulate to the inside. usually that means taking the sheetrock off, setting foam panels, strapping over and then new drywall.

    two more hints for you to pay attention to -

    one - you only think the first floor walls will remain largely untouched. Odds that your ceiling joists can handle acting as floor joists are slim to none. And you need a stairwell to get up there, right?

    two - you need to make sure that your foundation can handle the extra load of another floor. R U in an area that requires such engineering?

     

     

    Welcome to the
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    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

    1. jcresko | Mar 20, 2008 06:47am | #4

      Guys,Thanks for the input. The house is in Arlington, VA, so summer cooling is as important winter heating.....Regarding the air space (as drainage plane) - yes, that is my essential concern. However, when I replaced the windows (which I enlarged by removing masonry below allowing for taller windows), I noticed that the bricks were back buttered with a relatively thick layer of mortar. My understanding is that this was done to increase water penetration resistance, and I believe it works very well. I guess the basic question I have is - why not insulate that space with closed cell foam? It cannot absorb water, and would act as a vapor barrier, right?Regarding 2nd floor addition structural issues - joists are 2x8 and this will be improved, likely by adding an additional floor deck. 2nd floor additions are very common here- the masonry walls make for a solid base. The stairs will be located in a small addition on one side of the house, that will also act as the entryway from driveway, mudroom, etc.Joe

      1. Riversong | Mar 20, 2008 06:55am | #5

        Both brick and block can absorb large amounts of moisture, whether from interior diffusion or from exterior rain.  They need to breathe.  That space is there for a good reason. 

        Riversong HouseWright

        Design *  * Build *  * Renovate *  * ConsultSolar & Super-Insulated Healthy Homes

        1. DaveRicheson | Mar 20, 2008 07:38pm | #6

          We commonly use foam board over block and then a brick veneer in new commercial construction in this area. On retros and remodels the foam is most often added on the interior.

          We are in a mixed climate much like Virginia's, so there are fairly even heating/cooling cycles. With the porosity of both the brick and block I have often wondered which direction the water and vapor is being driven, depending on the season. The loose applied foam panels would not cause much of a change, but like you, I think a close cell spray foam would definitely change the physics of were the water of vapor is headed.

      2. reinvent | Mar 20, 2008 10:02pm | #7

        Maybe these guys have a suggestion we dont know about.http://www.imiweb.org/index.htmhttp://www.masonryconstruction.com/

      3. Piffin | Mar 20, 2008 11:43pm | #8

        "I guess the basic question I have is - why not insulate that space with closed cell foam? It cannot absorb water, and would act as a vapor barrier, right?"No
        The kind of foam that is pourable to get down into a less than 1" space 8' tall would be an icynene which is open celled and acts like a sponge when it gets wetted.Polyurethene foam is sprayed on instead of poured. It is waterproof, but it expands as it cures so it could conceivably push the brick veneer away from the block.And you would then have no drainage plane. As much as it might seem that you have no need for it, instances of water damage due to eliminating it are common.
        Tho I admit that your block would be less likely to grow mold and rot out than a framed wall would."2nd floor additions are very common here- the masonry walls make for a solid base. "Not really - the footing is what makes your base 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  4. User avater
    CapnMac | Mar 21, 2008 12:40am | #9

    Does anyone have advice on insulating between the brick and block (about a 1 inch space)?

    Yes, leave it alone.  If that space was detailed correctly (and it sounds that way from your description), that area is there to collect any moisture that either of the masonry surfaces collects, and pass it down to the bottom of the wall where it escapes to daylight by way of weeps (either an actual gap between bricks or an embedded fiber in the mortar).

    Ok, so that's not getting you any additional insulation.  If the CMU (concrete masonry unit, aka "cinder block") are hollow, you could gain some R value by filling them--but you will have places you just will not be able to reach from the top (under window sills especially).

    What that leaves you is going to some form of rigid foam either over or upon lath/sleepers/strapping on the inside of the walls.  Your speciific climate would then determine what perfomance improvement that would net you.

    Occupational hazard of my occupation not being around (sorry Bubba)

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