Hi! We have a client who has a conditioned apartment over a garage. We are adding rigid foam insulation with 1/2" gyp in the interior, the garage is unconditioned, but there is an exterior finish and insulation between the two floors. On two of the 4 exterior walls, the CMU is just painted. I am a little worried about there not being a proper moisture/vapor barrier on the exterior. Is this concern unreasonable? Is there a particular type of paint that we should use to ensure a water tight envelope?
"I am a little worried about there not being a proper moisture/vapor barrier on the exterior" - Just a little worried?
"Is this concern unreasonable?" - A little worried =/= concerned in my book... but regardless, no. your concern is most certainly reasonable
"Is there a particular type of paint that we should use to ensure a water tight envelope?" - Paint? No. That's not how building envelops work... Sure, plenty of self-adhered or torched-on membranes are available and perhaps you could get away with a proper stucco assembly but no. There is no quick and easy (and cheap... and pretty) way to turn the exterior of a CMU garage wall water-tight.
Pro-tip... never a good idea to create a situation where you might trap water/vapour in an existing wall assembly. Plenty of fun things happen when existing walls are suddenly forced to dry-out in new and unpredictable ways.
How thick do you make the waterproof paint layer in your revit wall assemblies? Perhaps a separate wall family all-together so that you can accurately trim it around openings. Probably best also to model each CMU individually.
Specifically, Figure 22 (the last assembly in the article).
Jan 5, 23 11:41 am ·
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Non Sequitur
"Water control layer Painted stucco rendering on CMU. The CMU wall behaves as a “mass wall,” storing moisture during rain events, then drying during more favorable periods."
We're currently in our 2nd flash-freeze/rainstorm of 2023. Such an assembly would last less than a hockey period in my area...
Jan 5, 23 12:02 pm ·
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t a z
For a Mid-Atlantic climate stucco may survive, but mold could be more of a persistent issue if the wall is shaded for considerable amounts of time. Still, agreed, I'd try to find something better than stucco to act as water/air control layers on the exterior.
Jan 5, 23 1:39 pm ·
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CMU walls - conditioned inside, exposed outside
Hi! We have a client who has a conditioned apartment over a garage. We are adding rigid foam insulation with 1/2" gyp in the interior, the garage is unconditioned, but there is an exterior finish and insulation between the two floors. On two of the 4 exterior walls, the CMU is just painted. I am a little worried about there not being a proper moisture/vapor barrier on the exterior. Is this concern unreasonable? Is there a particular type of paint that we should use to ensure a water tight envelope?
Thanks!
Aubrey
"I am a little worried about there not being a proper moisture/vapor barrier on the exterior" - Just a little worried?
"Is this concern unreasonable?" - A little worried =/= concerned in my book... but regardless, no. your concern is most certainly reasonable
"Is there a particular type of paint that we should use to ensure a water tight envelope?" - Paint? No. That's not how building envelops work... Sure, plenty of self-adhered or torched-on membranes are available and perhaps you could get away with a proper stucco assembly but no. There is no quick and easy (and cheap... and pretty) way to turn the exterior of a CMU garage wall water-tight.
Pro-tip... never a good idea to create a situation where you might trap water/vapour in an existing wall assembly. Plenty of fun things happen when existing walls are suddenly forced to dry-out in new and unpredictable ways.
You're not that guy pal, trust me
which guy am I not?
I have seen people do a fluid applied coating on the interior face of the CMU and the apply the insulation, furring and gyp. board over it.
You will need to do some homework to find out if this would work properly in the climate where the building is located.
We've done similar application to CMU walls in high humidity spaces like public pools and saunas.
What climate zone are we talking about here?
Temperate Climate Zone, Delaware by the beach.
No moisture there.
Details! Sketch up some details.
How thick do you make the waterproof paint layer in your revit wall assemblies? Perhaps a separate wall family all-together so that you can accurately trim it around openings. Probably best also to model each CMU individually.
Yes and yes.
^ We had staff in our office that modelled 1mm thin assemblies for paint.... walls and ceilings. It was a bloody nightmare.
So no one ever heard of split face and then paint then?
They did not. They also work elsewhere.
I would poke around here to investigate relevant guidance:
Building Science Corporation | Consulting & Architecture
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-120-understanding-walls
Specifically, Figure 22 (the last assembly in the article).
"Water control layer Painted stucco rendering on CMU. The CMU wall behaves as a “mass wall,” storing moisture during rain events, then drying during more favorable periods."
We're currently in our 2nd flash-freeze/rainstorm of 2023. Such an assembly would last less than a hockey period in my area...
For a Mid-Atlantic climate stucco may survive, but mold could be more of a persistent issue if the wall is shaded for considerable amounts of time. Still, agreed, I'd try to find something better than stucco to act as water/air control layers on the exterior.
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