Hi guys… I’m an inspector in eastern Washington and am not very familiar with Stucco.My nephew in California is having a house built using stucco as the exterior finish. I noticed in the picture he sent that the OSB backing does not cover 100% of the exterior wall. In my research I see that a water resistant barrier is required but no info on the OSB backing requirements. Seems like it should completely cover … what are your thoughts please?
OSB backing ? do you mean exterior sheathing? if it does not cover the wall entirely, what covers the rest of it? Traditionally, a hard stucco should have at least 2 layers of building paper (or similar) behind it whenever installed over wooden wall. If there is no water barrier between the stucco and OSB, the OSB will rot in a jiffy. Stucco is not a waterproof cladding. Also important to recognize the type of stucco.
Some pictures would probably help.
The stucco has not been applied yet. There are OSB Pieces along the bottom edges and around the doors/windows but the exterior sheathing (OSB) is not 100%. The rest is covered with some kind of tar paper. (Can’t tell from the pictures) There are several homes being built and all are the same. I will try to get some pictures uploaded. I’m also taking the advanced stucco course to see if I can find an answer. Thanks for your help.
There is the moisture barrier paper with wire in it but no osb on the studs. It looks to me like they plan to use the stucco as the exterior wall without complete OSB coverage…
It appears they will stucco without structural wood panels (sheathing). This is an older, less expensive, practice and is still allowed in many areas. Having solidly sheathed wall behind stucco, especially in seismic and high-wind areas, is highly beneficial. It helps the wall remain flat, minimizes cracking, and braces the wall better to prevent racking.
I would talk to the local building department to see if this is allowed in their area and what they think about it 
Also check the building plans to see if in fact no sheathing is called for. Lastly, if this was my house, it would have solid sheathing. Build once, build well!
Thanks for your help! It’s what I feel as well build once build well!
If the exterior wall has no sheathing, diagonal bracing should be installed to keep the wall from racking
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There was a couple of contractors or should say developers that used this (cheap assed) method in our area back in the 90s. I guess it is still allowed as long as you have the other types of bracing for Shear loads…
However I can easily See visually which of these homes were done this way and I will call it how I see it; A Cheap Practice that will show visual problems as well as being very susceptible to physical damage.
One I inspected showed signs of damage from kids playing basketball nearby. The errant ball easily cracked the stucco in several areas. Yes, mostly just cosmetic, but is a cheap shortcut way of doing things (IMO).
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Thanks Larry thats what I think as well.