Plywood versus OSB for exterior walls?
I am planning an addition to my house which will have a 500ft basement with 2 floors above it. The exterior walls are 16 ft by 22 ft. The basement will be concrete, and will have brick cladding for the above grade portion (as an aside, the single layer of brick cladding has no gap but is directly applied with mortar to the concrete – what do youthink of that?). The first and second floor will have stucco cladding. Now, my architect has chosen this for the exterior: 3 coats portland cement plaster (stucco), metal lath, 2 layers of 60 minute grade D building paper, 1/2″ external grade plywood sheathing (specified no OSB) applied horizontally with 1/8″ minimum space between adjoining sheets, wood stud framing (2×4 and 2×6).
I was surprised to find plywood being specified, since I have seen multiple references on Building Science to plywood as a thing of the past (“sadly those days are gone forever” would be a typical reference to plywood sheathing). Am I right that this is a cost issue? It’s all about OSB and foam now is what I find. It seems my architect specified plywood due to the use of stucco “in accordance with the requirements of ASTM C 926 and recommendations of Portland Cement Association (PCA).”
So here is my question. I am on a tight budget, replacing plywood (about 900 sq ft of sheathing in total) with OSB and rigid foam combination might be a big cost saving, plus be giving me very desirable exterior insulation for the frame. (This would be either foam and OSB all around or perhaps 2 layers of foam changing to one inch of foam and one inch of OSB on the corners for shear strength, as I read on Building Science). I also read EIFS is coming back having solved the vapor and drainage issue. What would be your suggestion as to the best approach? Do the new foam/OSB/EIFS options have the durability of plywood? I’d obviously want the most economical way, so long as it is durable.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part