Are vapor barriers (e.g., Tyvek) and weep screeds required for stucco on ICF as they are for conventional stick construction under IRC 730.6? Thanks.

What is the material being applied over the EPS? Is it vinyl siding, stucco, brick?

> Are vapor barriers (e.g., Tyvek)
I suggest that Tyvek is specifically designed to not act as a vapor barrier.

I've always applied mine directly to the icf

Concrete walls are exempt from the requirements for secondary weather barrier that wood buildings have.
See IRC 2009 Section 703.1
or IBC 1403.2, Exemption #1.
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Are you spec'ing this personally for your own house or is an Architect designing for you? An Architects Association has had concerns regarding this matter and if he designs and stamps it, it will most likely require a drainage layer of some sort, or his E&O will not cover it.

There is a difference between the "secondary weather barrier" (i.e.; Tyvek or building paper) and a "drainage layer". The drainage layer is actually a small gap created between the finish material (stucco or cladding) and the sheathing (or ICF). This "gap" technology is sometimes referred to as a "rain-screen", and actually provides a gravity-driven escape path for bulk (liquid) water.

In the coastal areas of BC, we are required to strap the exterior of buildings with a 10mm (3/8") furring strip over the top of the building paper that creates this rain-screen gap. This idea is gaining traction in other areas that are prone to wind-driven moisture intrusion in buildings.

The stucco (EIFS) guys use a recycled plastic matting that sort of looks like steel-wool under a microscope. The mechanically fasten the mat to the building and then apply their base-coat.

One might think that this would be a silly idea in an area that is hot and dry most of the year......wrong on two accounts: 1) Those areas sometimes have short, but quite intense, periods of heavy precipitation, and 2) the air gap behind the cladding allows for venting of heat that can build up in cladding materials, which can cause expansion and warping.

All in all, the notion of multiple (or redundant) means of increasing the building's "Drying Capacity" is a good thing.
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BTW: I see earlier posts refer to Tyvek as a "vapor barrier"..... it isn't that at all. The secondary weather barrier (Tyvek or building paper) is a back-up means to keep bulk (liquid) water out of the building if (when...) the cladding fails. These materials are quite permeable in terms of water vapor.

IF (yes....if..) a vapor barrier is employed, it typically is on the warm side of the wall (in heating climates), and consists of a membrane or paint that carries a very low permeability rating. This layer is designed to stop airborne moisture (vapor) from being driven through the wall by pressure differential. We all know what happens to a cavity wall loaded with "pink" when moisture enters the cavity. This is the beauty of ICF..... no cavity.....no vapor drive.
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Just checking but:

"2) the air gap behind the cladding allows for venting of heat that can build up in cladding materials, which can cause expansion and warping. "

Really? How are you going to get any significant cooling of the EIFS skin with 10mm of (fairly insulating, but air permeable) plastic fiber matting, even if you DID vent the top & bottom of the rainscreen cavity to promote convection?

The air doesn't have to move very fast to purge moisture but it needs real cfm to provide any convective cooling. I'm not buying that argument, but if you have data, I'll consider it.

Also:

"We all know what happens to a cavity wall loaded with "pink" when moisture enters the cavity. This is the beauty of ICF..... no cavity.....no vapor drive. "

Huh? You seem to be confusing the differences between vapor pressure drives and air leaks driven by air-pressure differences. They're not the same thing, not even close!

Water vapor pressure has nothing to do with air permeabilty or air-volumes or air movement. The presence of cavity neither creates nor mitigates a vapor pressure difference, whether it's air-leaky or not. The vapor pressure is all about the differences in the absolute humidity of the air on either side of a boundary or assembly. The pink stuff (and all other fiber insulation) is highly permeable to water vapor, so it's the vapor retardency of the interior & exterior cladding stackups that allow a vapor pressure to develop, and what determines the rate of moisture transfer through the assembly via diffusion. While there can be a temperature difference across the fiber, the high permeance means there is never a substantial absolute moisture difference between the two sides.

That's not dramatically different from an ICF- the center material (concrete) is highly permeable to moisture, and the moisture content at the interface with the EPS on either side is identical. EPS is modestly vapor permeable- a 2.5" skin of Type-II EPS runs about 1.5-2 perms- not much tighter than standard latex paint, a Class-III vapor retarder. With an R21 ICF (2.5" + 2.5") that still only drops to about 1 perm, a minimal Class-II vapor retarder against exterior moisture drives, but it's still only a Class-III vapor retarder against ground moisture wicking up the concrete from the footing. (Capillary breaks between the footing & wall are important, even with ICF.) The interior claddings will often be susceptible to moisture damage.

But the air-tightness of stick built assemblies matter. Gross bulk-air leaks into the wall cavities in a stick-built assembly that is poorly constructed can move a lot more moisture into the assembly than vapor diffusion due to vapor drives through even unpainted wallboard. A square inch of air leak can transfer a whole wall's worth of vapor drive moisture through standard latex paint. But that's an air leak. Not a vapor drive.

The advantage to ICF moisture resilience over stick built has nothing to do with vapor drive,it's the fact the at the structural elements (concrete) isn't susceptible to damage by moisture the way wood sheathing & framing is. But that doesn't mean you don't have to air & water seal the structure, and manage ground moisture to not damage the parts of the stackup that ARE susceptible- the interior-side finish wall materials. (And yes, vapor permeance is still an issue, cavity or no.)