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Old 03-09-2013, 08:45 PM   #1
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Can you insulate timber frame wall cavity with brick fascad?


I am remodeling my bathroom. There is 1 exterior wall in the bathroom with no insulation. I am taking down 75% of the drywall/plaster on this wall so I can install new tile. I think it makes sense to take the remaining 25% down and fully insulate the 2x4 cavity. But I have some concerns regarding vapor barriers and potential for water damage/mold.

The current makeup of the wall from exterior to interior is as follows:
  1. brick, 4" thick
  2. air space, (not sure how big)
  3. tar paper
  4. tongue and groove wood clapboard
  5. 2x4 stud cavity
  6. drywall
  7. plaster
I think the tar paper is a vapor barrier.

I guess my options are:
  1. Install kraft faced fiberglass insulation in the 2x4 stud cavity with the paper facing the interior.
  2. Install un-faced fiberglass insulation in the 2x4 stud cavity.
I am concerned both options are not good. In option 1, I would be sandwiching the fiberglass insulation between two vapor barriers. I believe that is a no-no.

In option 2, the tar paper is on the wrong side of the insulation so as warm humid air from inside makes it way through the fiberglass it will cool and condense when it hits the tar paper.

Is there a right way to do this?

http://stevebouza.com/images/house/demo1.jpg

Another thing to consider, I will be tiling most of this wall because part of it is an alcove tub/shower. I will be applying a liquid membrane (hydroban) to the cement board underlayment. I think the hydroban is another vapor barrier, do I need to factor that into the insulation equation?

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Old 03-09-2013, 09:57 PM   #2
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Can you insulate timber frame wall cavity with brick fascad?


Best way I would say spray foam, dura rock then tile.

You could fiberglass, 4 mil plastic then dura rock ( green board at a minimum)

Don't worry about trapping moisture. the tar paper has long since been a good barrier and the brick is going to suck up the moisture.

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Old 03-10-2013, 12:05 AM   #3
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Can you insulate timber frame wall cavity with brick fascad?


The building paper (Water Resistive Barrier) has a perm value of 30, very open when wet. Your wood sheathing boards are 10 perms, open also. pp. 3. Your location, Zone 5, does not require/want a vapor barrier/retarder on the inside as it is now a "flow-through" design. NO plastic or asphalt paper-faced batts, period, pp.11, fig. 3a, because it is so vapor open; http://www.buildingscience.com/docum...nd-wall-design

No poly/plastic sheeting or paper-faced batt behind "greenboard"; http://publicecodes.cyberregs.com/ic...002_par013.htm

Hydoban on inside is fine, nothing else behind the board. Always check with local AHJ.

Gary
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Old 03-11-2013, 09:33 PM   #4
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Can you insulate timber frame wall cavity with brick fascad?


Thank you for the replies.

That was quite the read Gary. Doing my best to follow it. I do have one question. In my original post I mentioned using fiberglass insulation. Upon further research I found a better product to use. Roxul ComfortBatt R15 stone wool batts (available locally) at a small price premium to fiberglass.

Now my question is, is this ComfortBatt still permeable enough for my wall cavity? I had difficulty finding exact specs for the product but the manufacturers website, however they did state "Roxul insulation is moisture resistant yet vapor permeable." Key word there being vapor permeable.
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Old 03-13-2013, 12:07 AM   #5
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Can you insulate timber frame wall cavity with brick fascad?


I'd check locally with the Inspector may let you slide due to wall make-up (coating) or ... they may require a Class 2 vapor retarder/barrier; http://publicecodes.cyberregs.com/ic...001_par003.htm

As you are in Zone 5; http://publicecodes.cyberregs.com/ic..._11_par002.htm

Good one is C.T.'s "Membrain" (Class 2) as it is variable perms, unlike plastic. http://www.bestofbuildingscience.com...3-4_p37-40.pdf

Gary
PS. Roxul is way better than F.G., IMO
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Old 03-13-2013, 09:25 AM   #6
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Can you insulate timber frame wall cavity with brick fascad?


Gary nailed it.

Membrain to the interior is a great option and be sure to detail out all your drywall for an airtight wall assembly.

While remodeling the bathroom, be sure to include plans for a fan (on a time preferably) for moisture control.

+1 on using Roxul or similar mineral wool in lieu of Fiberglass.

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