An air space is not necessarily required behind brick, stone or stucco and you can use 1/2" foam instead of 1" to make up some of the difference.

But while I agree installing foam on the exterior of the sheathing is a good idea, it may not make that much of a difference in your energy savings if you don't use it considering all you are already doing with the interior wall cavity insulation and exterior air barrier.

I agree with manhattan.

lions and tigers and bears..oh my!
(just couldn't resist)

"An air space is not necessarily required behind brick, stone or stucco"

But a proper drainage plane is so you will want to have a double ply underlayment, not just tyvek wrap. Tyvek makes a poor underlayment for stucco. The underlayment/lath/flashings are what keeps a structure dry along with the proper drainage plane by way of a weep screed for stucco and weep holes for stone and brick where they go all the way down to the base of the wall. On stucco, water or moisture is going to condense behind the scratch/brown coats despite cracking. A faulty install of the underlayment/flashings/lath/screed is what will lead to rot of the framing members, not water through cracks. The use of a double ply underlayment is helping to reduce this moisture as the scratch coat has a tendency to stick to the first ply that causes the condensation. On brick and stone, a drainage plane is equally as important as moisture and water will get behind them as well. This even happens in the low humidity of the desert, so double ply is a good practice

If you are going with a traditional 3-coat stucco cementious based application, talk to your builder about using an elasomeric or acrylic top coat over the scratch and brown coats. It flexes with temperature changes and lessens the chance for any cracking as long as the lath/underlayments/flashings are installed correctly and the scratch/brown coats are allowed to sit a minimum of thirty days before apllying the top coating.

I measured the brick shelf, it's only 3 1/2" from the plywood. I take it that is quite small? And no, there were no wall details in the plans from my "home designer," just elevations showing where the different cladding materials go.

I'm not sure what you mean about the size of the cavity, macv. Do you mean the inside wall cavity? It's 2x6 framing. Thanks all for the input! Also, I believe code here requires a vapor barrier on the warm side so I should have added that to our assembly.

Tyvek and other housewrap manufacturers make specific products for use as drainage plains behind stucco, brick and stone... so "Tyvek" or other types of housewraps can work and can be used.

Residential codes do not require the 1" air gap if the gap is filled with mortar.

That said, you can always increase the depth of the brick ledge by installing deeper brick angles on top of the ledge to give you whatever required depth you desire.

The angles will protrude beyond the existing brick ledge but probably not enough to be noticed or be a distraction.

The "air gap" is the "cavity" part of a "brick cavity wall system" and is the horizontal distance from the back of the brick to the face of the sheathing.

Regardless of what any building code says (see the link below for why the IRC and the earlier CABO codes have long been a very poor guide to brick cavity wall construction) it should be obvious even to an inexperienced designer that the cavity must be left open and unobstructed to allow these two different wall materials (brick and wood) to move independently or the brickwork will crack and it should also be obvious that water that inevitably passes through the brick must be able to run down the back side of the wall to the weep holes at the bottom of the wall without being blocked or transfered to the back-up wall by mortar bridges, filled cavities, or improper brick ties. It's not difficult if you remember that the brick expands when the sun hits it and water runs freely downward unless interrupted by bridging materials.

It is physically difficult to achieve a good brick cavity wall with only a 1" cavity because there is so little space for the mason's fingers and trowel therefore mortar bridging is virtually assured and a stainless steel tie might not fit. I strongly recommend a more abrasion resistant house wrap like Tyvek Commercial Wrap or even Typar.

If the brick shelf is only 3 1/2" deep at the foundation and the brick is a standard 3 5/8" width and a minimum 1" cavity is maintained then the overhang of the brick at the foundation would be 1 5/8" with only 2" of the brick sitting on the foundation. If the cavity is 3/4" then the brick would have 2 14" bearing and a 1 3/8" overhang. It's not impossible to build but it does not meet time honored industry standards like those from the BIA.

One thing you can be sure of is that there is no room for installing insulation in the cavity. The contractor just won that argument.

If the contractor insists on using galvanized corrugated brick ties be sure they are initially installed pointing downward so they will be bent outward as well as downward to contact the top of the brick course thereby avoiding a water bridge or the need to twist the tie 180 degrees which can damage the house wrap.

Here is a link that might be useful: Problems with Code-Compliant Brick Veneer in Residential Construction

I know of a building that had steel angles added to support the brick veneer and allow a larger cavity after the original brickwork cracked so badly that it had to be removed (it was grouted tight to the back-up wall).

I mention this not only because it is an example of a licensed designer and local building officials not knowing how to properly build a brick cavity wall but also because it looks terrible. The next time I drive by it I'll take a photo.

A "drainage plane" is often an appropriate feature for a wall cladding system that is tightly applied to a structure because it provides water drainage at the face of the structure where the weather/air barrier is located. Therefore, that drainage feature is often incorporated into some weather/air barriers by deformation, or thickening of the membrane or even by just two layers of building paper or housewrap. The degree of drainage needed should be determined by the amount of rainfall expected in the area and how porous the cladding is. In heavy rain areas this drainage plane feature can consist of strapping that supports the cladding but the materials are all still rigidly connected.

A "drainage plane" wall system should not be confused with a masonry veneer cavity wall system (sometimes called a "rainscreen") where a space or cavity is created not only to allow water to drain but to allow differiential expansion of the cladding and the back-up wall. This is necessary due to the unusual expansion of brick when exposed to the sun, etc. This movement is greater than for cement based materials and wood but less than for most plastics.

Treating a brick veneer cavity wall like a stucco clad wall by grouting the cavity and relying on some kind weather/air barrier material to provide drainage would be a seriously foolish mistake although I have no doubt it is allowed by building codes for single family residences and contractors like that approach because it avoids thicker foundation walls. Unfortunately, if it meets the building code and lasts a year, it becomes your problem not theirs.

I just realized my math was wrong. A 3 1/2" brick shelf with a 1" cavity would allow 2 1/2" of bearing and an overhang of 1 1/8" which is acceptable. If the cavity is kept clear and proper weeps, ties, and flashing are used, it will be a standard residential brick veneer cavity wall. The cavity can only be grouted below the lowest line of weeps and below the top of the foundation wall (no wood behind it).

I've never seen a brick venner application treated the same as stucco but have seen stone directly applied over the scratch/brown coats when coinciding with stucco and over it's own mortar/rib lath. Some use cement board these days, but the biggest concern is still the underlayments flashing. Since the op's project calls out for all three combined, they better know what they are doing, especially at transition points. Tyvek makes a rain screen type underlayment for stucco lathing, but doubling tyvek the product tends to stick to itself compared to a saturated double ply underlayment that is felt based. If going with tyvek, it would be better to have 30# saturated felt as the first ply.

A good underlayment for stucco is felt building paper covered by a cheap perforated woven housewrap like many lumberyards sell with their logo on it. It will stick to the stucco but allow water to pass easily through it. The base layer could also be Tyvek DrainWrap (same as StuccoWrap) but neither is a "rainscreen". A rain screen has a more substantial air space cavity that is vented to the outside.