How big of a rainscreen
user-6610113
| Posted in Energy Efficiency and Durability on
Building in climate zone 3, 20 miles from the shore in Southern California. Remodel with addition of a 100 year old stucco house with a 4’ overhang roof and parapet walls.
the existing stucco has felt or paper (I’m not sure) it.
For the remodeled areas I’m not sure what to use. options I’ve considered include 2 layers of paper, tyvek stucco wrap, Benjamin obdyke hydro gap or a larger rainscreen.
how big of a gap do I need in this area? Much of the stucco is well protected except for the balloon framed parapet walls.
Thanks for considering my question!
Matt
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Replies
Hi Matt.
The International Residential Code still allows for two layers of building paper as the WRB for stucco installations. Most experts agree that it is an inadequate code and the same is said for most of the drainable housewraps behind stucco. You need a true rainscreen product for the best chance at a long lasting stucco installation on wood framed walls. I suggest you read this: Rainscreen Products for Stucco Installations
>"...Benjamin obdyke hydro gap..."
That's only a 1mm drainage gap, which would all but certainly get clogged when installing the stucco.
Within the Benjamin Obdyke product lines the Rainslicker MAX would be the most appropriate:
https://www.benjaminobdyke.com/products/slicker-max-rainscreen-6mm/
The -MAX is pretty much identical to the Rainslicker Classic except that it has a fine mesh laminated onto the exterior side to keep mortar / stucco from getting in and clogging up the drainage path. (Even with shingle siding it's somewhat preferable to the Classic since it's better at keeping the insects out.)
Supposedly:
The industry is afraid to move for fear of admitting that their 10-year-old houses were poorly constructed and opening themselves up to massive lawsuits, but once it does move it will be converting to 1x4 furring strips underneath the stucco lath (0.75" airgap). BSC says that a much thinner airgap (1/4" or less) would be fine, but if anything bends even a little it will come into contact - how do you actually ensure that no bending occurs on the jobsite? Furring strips are cheap and easy to work with. Put down some sort of layer of WRB (tyvek? tarpaper?) beneath the strips.
Some builders assert that getting mortar / stucco pushed through into a gap (plugging the ventilation) is inevitable, some that it is preventable with enough care. If your stucco crew is sloppy, as most are, perhaps even put some kind of highly permeable rolled good (builder's paper? ramboard?) stretched between the furring strips in order to prevent push-through of the stucco just for the duration of its cure; It can rot away shortly after and will still have done its job.
This might be a good read:
https://www.buildingscience.com/documents/insights/bsi-029-stucco-woes-the-perfect-storm