Looking for the perfect setup for the Pac NW new house I've read many articles and manufacturer guides related to different materials, installation methods, .... that prevent moisture transfer into the building structure.  SIPs, ZIP Systems, wrappings, taping, ....  Wrapp manufacturers like DuPont and ZIP System put lots of stress on proper installation and taping.  My question is" since the house will receive stucco and stone finish the walls and the wrapping will be punctured thousands of times when fastening metal lathe.  Will the water/moisture not come slowly through these holes and penetrate into non vented wall cavity?  I know that the wrapps, ZIPs, .... slow down the moisture penetration but considering the amount of rain we get in here and the longer period of time the house is intended to stay I don't see how any walls punctured this way will hold against the moisture.  Am I oversensitive in this area?

You should have an air gap between your exterior stucco or stone and the wall. Perhaps in the form of a double layer of stucco wrap. Or something bigger.

Posted By jonr on 13 May 2013 08:37 PM
You should have an air gap between your exterior stucco or stone and the wall. Perhaps in the form of a double layer of stucco wrap. Or something bigger.

air gap sure thing but what about thousands of holes from the staples or nails that penetrate the wrap?  What good is the air movement if the water, in even smallest amounts, gets into the wall cavity?  Manufacturers of wrap, ZIP systems, ... stress that taping of any holes and gaps is critical - great, and so you do it and after all is beautifully taped the mason punctures the entire wrap fastening the lathe.  I just don't get it.

I don't have the answer, but to some extent, a hole filled with a staple or nail isn't really a hole. Now if someone is pounding in nails and then pulling them back out, you have a real problem.

BuildingScience Corporation, the preeminent building forensic scientists in America has ton of information on their website about the proper way to install Stucco. read it all. http://www.buildingscience.com/search?SearchableText=stucco

Moisture transfer from siding to the sheathing happens in two ways, bulk water wetting/capillary draw, and vapor transfer. The housewrap/felt is supposed to shunt the bulk water penetrations, but some are better than others in terms of capillary draw & vapor transfer. Crinkle-type housewraps are a much lower capillary break than the smooth types or felt, and are highly vapor permeable (unlike felt). An array of 10,001 fastener holes increases the capillary draw slightly but not much. Vapor transfer is a permeance x area kind of deal, and the net cross sectional area of the tiny rips around staples & nails is still miniscule. The air gap is a HUGE capillary break, and the housewrap is unlikely to get a sustained bulk wetting, and though there can be periods where sun-driven moisture siding can condense for a time on the housewrap (or sheathing), under most siding types those events are shallow and brief.

But under reservoir claddings like stucco or brick the vapor transport can dominate the moisture transfer picture where ever it gets direct sun, and it's useful to have a somewhat lower permeance product or variable permeance product there. The capillary break of maintaining sized gap is more critical, as is the moisture-purging capacity of the gap being fully vented so that it can convect easily when heated by the sun.

Now this is some great info. many thx guys.I feel much more confident in the entire process now. Cheers

Vapor transfer is a permeance x area kind of deal

I think it is most accurate to talk in terms of vapor diffusion and vapor transport via air in/ex filtration. Ie, 3 ways that moisture gets in (liquid water being the third and even that has sub types).

Not to hijack the thread but! Just a question out of curiosity, what kind of material (stucco?) is acceptable on an ICF foam exterior? Isn’t it applied directly to the foam? John

Just about anything can go on ICF. You can attach directly to the ICF anchor points. Stucco can go on directly over the foam, so it is easy and popular. There is usually some attachment of the stucco mesh that holds the base coat to the anchor points.

Posted By jonr on 14 May 2013 01:50 PM

Vapor transfer is a permeance x area kind of deal

I think it is most accurate to talk in terms of vapor diffusion and vapor transport via air in/ex filtration. Ie, 3 ways that moisture gets in (liquid water being the third and even that has sub types).

It's a bit squishy when you're talking about air-transported moisture through the compressed micro-tear at the nail penetrations of a highly permeable housewrap though.  The concern here is the exterior moisture drives of the stucco, more so than the interior side air leakage.

But you make the important point that if it's a studwall you can't make the exterior of the sheathing too vapor tight without running into mid-winter moisture accumulation in the sheathing from interior-side air leaks, even in that very temperate climate.

I agree. Warm, wet stucco can create a layer of high dew point vapor next to (or near) a layer that is there to protect the wall. Either diffusion or air/vapor infiltration can allow the moisture through that barrier layer. The former is something that you usually don't want to block, but ventilating away the stucco's moisture works. Air/vapor infiltration is usually the more significant concern . And of course capillary action and bulk water flow can let liquid water into a wall.

I have heard that films like Tyvek are susceptible to having staple and nail holes enlarged by wind.