Rigid Foam insulation R-6 with Stucco

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Old 08-20-14, 06:47 PM
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Rigid Foam insulation R-6 with Stucco

For stucco walls, isn't it common practice to use rigid insulation as underlayment to prevent cracking of the stucco?
 
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Old 08-20-14, 08:20 PM
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Foam can be installed beneath stucco systems or EIFS (exterior insulated finish systems) but it certainly is not a requirement for crack resistance. A significant number of stucco jobs today are installed as traditional three coat stucco systems consisting of a scratch coat, brown coat and finish coat all over expanded wire mesh or wire lath attached directly to the sheathing.

The finish coat can be either a pre-blended synthetic material or portland cement finish or a site blended cement finish coat.

Foam has nothing to do with the ability of the stucco assembly to resist cracking, it is there to provide the added R-value in a stucco assembly. If it is used in a thin coat assembly such as "Dryvit", then it serves as a base to which the coatings are applied but crack resistance is provided by the inclusion of a mesh material into the base coat of the assembly.

The R-value of the foam is not important to the integrity of the stucco or synthetic finish system.
 
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Old 08-20-14, 08:57 PM
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attached directly to the sheathing.
well, not "directly"... (over 2 layers of Grade D or 15 lb felt, according to code)

Foam has nothing to do with the ability of the stucco assembly to resist cracking
exactly!
 
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Old 08-20-14, 09:58 PM
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So the Foam is not a requirement for stucco walls?
 
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Old 08-20-14, 10:35 PM
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It depends on what "you are calling stucco".

Re-read Calvert's reply and clarify whether you are talking about traditional masonry three coat stucco or whether you are talking about EIFS, which is always installed over foam.

Foam "can" be used under masonry three coat stucco, but nothing says it HAS to be used.
 
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Old 08-21-14, 05:00 AM
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Thanks X for that note about about the water resistant barrier behind the stucco.

Believe it or not, there are really manufacturers that do not require EIFS to go over foam. I have seen it applied directly to wood based sheathing materials.

Do I agree with that approach....hell no, but I have seen it, questioned it, been told it's OK, then seen it fail. But, it may work in some climates. Maybe someone else has seen and can attest to the sensibility of doing it.
 
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Old 08-21-14, 05:14 AM
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Locally, I've seen a lot of 'dryvit' exteriors where the stucco was applied directly over cement board. I've also painted for some builders that had the stucco guy install stryfoam in select areas to build it out for design features.
 
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Old 08-21-14, 04:00 PM
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Yes I have seen the EIFS materials used directly over wood OSB in fact. I figure it is only a matter of time . . .
USG used to have a system using their Durock cement board and some of their matirials for the base and finish. They don't market that system any longer.
It can probably work over cement board with the joints taped and an acrylic/Portland dement basecoat. I sure would be wary until it is proven.

There is another tread in this section about installinf stone tile over stucco. We are still wanting to know what kind of stucco the OP has on his walls. There are a lot of things called "stucco" these days that are not.
 
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