I am always hearing about the Perm Rating of walls and wanted to know if perm rating of masonry walls is something that is a big concern in Florida?
The Perm rating of stucco is a red herring. Climate zones 1 and 2 strictly LIMIT the perm rating of vapor barriers because you don’t want to trap moisture in the wall. Standard stucco is a Class III Vapor Barrier with a perm rating between 5 and 10 which would also make it a Vapor Permeable which is better yet in Florida. Stucco is accepted as a suitable weather barrier throughout the code – and that is what you are looking for in climate zones 1 and 2 – a weather barrier – not a vapor barrier. Check out 1405.3.1 and 1405.3.2. The code is RESTRICTING the perm rating of vapor barriers – not requiring low perm barriers. Stucco, and CMU, serves as a good weather and air barrier. If you are keen on low perm vapor barriers then move up North. We don’t need them in Florida.
This was a comment by a Florida Building Official on waterproofing block walls.
"Masonry is by it's nature porous and is not a good vapor barrier. My assumption is that in addition to the Tyvek, some sort of siding, brick or other finished material is planned other than stucco. " What are your thoughts?
You would never put tyvek on a masonry wall. I have never heard or seen such a thing. The code does not require a “vapor barrier” on cmu . Your block either has integral water repellent in combo with an exterior sealant/paint ----- or ------ it is stucco’d in which case the stucco and paint in combo with the cmu becomes the water/vapor barrier ------ or---------- you put brick on the outside with a roll on barrier ------ or---------- if you are using direct adhered stone or thin brick you use a product that seals the wall and adheres the stone or thin brick.
In all cases, other than at cracks - which need to be addressed in the design, the wall is water tight and sufficiently vapor tight to keep the interior dry.
Jerry Painter, FASTM
Don Beers, PE, GC