Moisture Barrier for Partially Below Grade Grouted CMU Wall

sequoia_2007July 5, 2009

We gutted our kitchen as part of a repair to our foundation. While removing the drywall from the wall separating the kitchen from the garage we discovered the sole plate for the wall rested 24â above the floor and the drywall was not fastened to the grouted CMU wall. We asked the contractor who rebuilt our floor to use a moisture barrier between the plywood and the grouted CMU wall and he left us the rest of the roll. The moisture barrier is the black sheet material rising from the floor in the photo above.

The soil under the garage slab starts about 12â below the sole plate. We thought we would add another section of the moisture barrier from the sole plate down to the floor. Does the moisture barrier need to overlap the layer of moisture barrier below and by how much? Next we would fur out the wall with 1x4. Do the furring strips need to be pressure treated? Finally we would cover with 5/8â moisture resistant, fire code drywall.

Is this the best code compliant approach under the 2006 International Building Code?

Thank you for taking the time to read my post and consider my questions.

Howard

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manhattan42

5/8" fire rated drywall is not required under the 2006 IRC. Only standard 1/2" drywall is required between the garage and habitable interior space.

The moisture barrier should also not be required on the interior side of the CMUs provide they had been dampproofed or water proofed on the garage/soil side.

2006 IRC requires any lumber that comes into contact with masonry walls below grade to be preservatively treated.
This means your furring strips would need to be presevatively treated.

    Bookmark   July 5, 2009 at 10:45PM
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sequoia_2007

Thank you for taking the time to respond.

Since we have to use 5/8â fire code rated drywall on the wall to the right we decided to use it on all the kitchen walls.

Based on the original drawing for our home there is a moisture barrier shown below grade on the garage side of the CMU wall. It appears to be intact since we get heavy effloresce on the surface of the garage slab, but the interior side of the wall does not show effloresce. Also, when we removed the kitchen drywall that was in contact with the CMU wall there was no sign of moisture.

Regarding the use of pressure treated furring strips. It sounds like we only need them if a moisture barrier is not provided. If a moisture barrier is provided then we can use untreated lumber?

Howard

    Bookmark   July 6, 2009 at 2:02AM
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manhattan42

"Regarding the use of pressure treated furring strips. It sounds like we only need them if a moisture barrier is not provided. If a moisture barrier is provided then we can use untreated lumber?"

Yes.

Only when lumber is in 'direct contact' with masonry walls below is preservatively treated lumber required.

As long as you place the impermeable 'moisture barrier' between the furring strips and CMUs, no treated lumber furring strips are required.

However, if this 'moisture barrier' will also be a 'vapor barrier', it will be located on the wrong side of the wall assembly and could cause unwanted condensation problems.
(A 'vapor barrier' should be install on the warm-in-winter side of a wall assembly immediately under the drywall and immediately over the studs or furring strips.)

It is likley a better "code compliant" installation to simply use treated furring strips and no mositure barrier at all.

But for such a small area, should not matter much either way you choose to do it.

    Bookmark   July 6, 2009 at 10:12PM
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sequoia_2007

Sounds like our best approach is to use pressure treated 1x4 furring strips running from ceiling to floor. We will use insulation in the stud bay above with the vapor barrier facing the drywall. No insulation between the drywall and CMU wall. Do you recommend any type of coating for the interior side of the CMU wall before we attach the furring strips?

Thanks,

Howard

    Bookmark   July 6, 2009 at 10:48PM
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