Hello Everyone,

First, this question relates to climate zone 5 here in southern New England.

I’m currently working through preliminary details with an architect on a residential project with a substantial amount of “full-thickness” stone veneer. The structural system is primarily a steel frame with slab on metal deck floor systems. The architect has allowed for 8″ of buildup in the stone veneer layer, which we have recommended be broken down into a buildup of 2″ of Mineral wool board, 1″ of drainage matt, and 5″ of full thickness veneer. This is all mostly in an effort to minimize thermal bridging at many of the steel components within the exterior structural wall.

Where our opinion differs is on the composition of the backup wall in this assembly. Since the exterior walls are non-load bearing, given the steel structure, we are recommending to frame these with engineered lumber or metal stud, use a cementitious sheathing w/ a vapor open WRB, and use a thermally broken veneer tie through the continuous insulation layer, similar to Hohman & Barnards Therm 2-Seal Tie. This would allow for the balance of the thermal insulation to live directly behind the sheathing, and would likely be comprised of a closed cell spray foam.

The architect would like to incorporate a 6″ CMU backup wall into this assembly instead of the framed wall, creating the need for a secondary framed cavity to the interior for the balance of the thermal insulation and mechanical services.

We think this is a redundant approach and only adds unnecessary cost to the assembly. The architect is concerned about moisture issues wood assembly leading to failure of the stone veneer.

Questions for the group:

1] Am I missing anything in our proposed assembly that I should be concerned about recommending?
2] Does anyone have any sources/research I could point to for full thickness veneer assemblies similar to what we’re proposing?
3] Would Plywood be perfectly acceptable in the stud wall approach instead of a cement board sheathing?
4] If the architect insists on the CMU backup wall, what approach should we take for a weather barrier/waterproofing system? Would anyone recommend a fluid type product over a self adhered membrane?

Thanks for any input.