WRB Behind Cement Board Stucco
Hi everyone, looking for any insight you can provide on this..
Climate Zone 7A – Wall in question faces East (very slightly SE)
We are scheduled to have our stucco install start next week. Currently our front of house is wrapped with Tyvek HouseWrap WRB over OSB sheathing and our contractor will be applying cement board stucco (Durock/Permabase) starting next week.. However, after doing some research I’ve noticed many concerns raised re. Tyvek housewrap behind a stucco application.
I’ve read up on the rainscreen approach, unfortunately no one in town carries the product in stock and I cant get it in prior to our install date.
With that being said, any recommendations or advice to better prepare WRB for stucco?
– Would a second layer of Tyvek be of any benefit? OR would there be any downside to two layers of Tyvek?
– #15 Paper over the Tyvek WRB?
– Would the use of cap staples create any slight benefit of a drainage space separating the cement board from the WRB?
The wall faces mainly east (slightly SE). Not exactly a rainy climate (zone 7A) but we do get the occasional wet/rainy periods.
Thanks in advance for your help
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I'm just a DIYer. Maybe a pro will post too.
Are you stuccoing your house or putting cement board on? Stucco directly on to tyvek is supposedly trouble because it sort of bonds to the tyvek and the tyvek no longer acts as a proper wrb. A second layer of tyvek or a layer of tyvek stucco wrap (which should be readily available by special order from most lumber yards) seems to be the recommended solution and what I did on my own house for some patch work: regular tyvek then tyvek stucco wrap to make a poor mans drainage gap.
I'd also say if your tyvek is old or poorly installed, a new second layer of tyvek on top of the old seems like cheap insurance.
But it doesnt sound like you are stuccoing onto the tyvek. It sounds like you are putting cement board on? I don't see the problem with tyvek behind your cement board.
Caps behind your cement board sounds like a nightmare for a flat install. If you want a drainage gap, why not make one with 5/8" or 3/4" strapping (but see the list below for planning for the increase in your system thickness).
Where is your exterior insulation though? Skipping it based on climate or the technical details?
Why not consider this:
- existing sheathing
- existing tyvek with a seam tape refresh as needed
- 1" or 1.5" eps foam board
- optional strapping for that drainage gap
- cladding (whatever that is)
The details to pre plan would be:
- window jamb and sill extension
- termite/insect protection at the bottom of the foam board or drainage gape
- temporary affixing of foam board if you aren't strapping it
- having adequate length cement board fasteners to pass through the assembly
- wall to roof intersection details (troublesome on zero overhang)
- any corner intersections with existing wall systems you arent planning to renovate.
I'd be sure my builder had those details nailed down before thinking about exterior insulation. Of course, if the cladding thickness is changing on one side of the building you already have half those issues to plan for.
Hope that helps.
#15 felt (#30 better or JumoTex60, more so) is a good WRB. I would get Tyvek StuccoWrap, as the wrinkles create a draining path.
My concern is with your choice of materials in stucco for a CZ7 house? Stucco damages often with freeze cycles, and repairs and/or resurfaces are needed to be done regularly. I learned that living in the SW for many years and designing and building "pueblo" homes in CZ2-5. I imagine it gets worse in CZ7.
Rick,
Like Armando, I'm worried about your choice of cladding, as well as the ability of your local contractors to address potential moisture entry issues.
I think that installing stucco without an air gap between the stucco and the sheathing -- especially on a wood-framed home with OSB sheathing -- is extremely risky. For more information, see this article: To Install Stucco Right, Include an Air Gap.