Vapor Barrier With Concrete Block Walls? - Insulation - Contractor Talk

Vapor Barrier With Concrete Block Walls?

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Old 04-21-2010, 11:40 PM   #1
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Vapor Barrier With Concrete Block Walls?

In assessing a bathroom remodel that I'm about to tackle, this 1940 home's bathroom in question has 2 exterior concrete block walls. These concrete block walls are not your average 8"X16" block. They are some 1940's robust version, that the homeowner said may be called "diamond" block. I am planning on completely gutting the room to start, and rebuilding with solid foam insulation up against the block in between the 2X4 studs (laid flat against the block wall, which currently the plaster wall is built upon. (currently there is a 1 1/2" or 2" empty cavity between plaster and block with studs laid on flat side for framing.) Now my question.... in between the framing and new drywall, should I be installing a vapor barrier? Location is Los Angeles, but not hot side of's the cool side of LA, maybe 85 degrees on the hottest day of the summer, but usually mild at 60-75. The block wall is painted on the exterior, and nothing else in-between. My concern lies in last summer's remodel at this house. In demo'ing another exterior wall in the same house, I encountered PLENTY of efflourescence which leads me to believe that there's plenty of vapor transmission through the block wall. Now, in this case it could be due to the fact that this wall was partially buried by soil, and was also a wall inside of a laundry closet. My inclination is to leave out the vapor barrier in the bathroom to let it breathe mildly, but installing the foam insulation panels in-between the studs to help keep the inside warm in the winter months (when it's 50 degrees outside) Regularly the block walls transmit so much of the outside cool weather that it cools the bathroom uncomfortably for much of the slightly warmer day....hence the insulation. I'm planning 1.5" or 2" thick (depending on existing stud size) foam panel for insulation, or should I use fiberglass in this case? Which will get me better insulation in this unusually small space?...and VB, or no VB? This area in question is not sub-terranean, and has very low exposure to sun/wind/rain.
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