[cvdukes]

PF,
First, I'll have to say that I am little leery about using the wood wall to take the primary weight of your oven. No matter how well its pressure-treated, it all eventually rots ... I can't say much for the lifetime guarantee most pressure-treated wood comes with, I think the manufacturers count on you not being to prove it actually came from them.

Also, I think most preference would be for the hearth to be a little higher than 32 inches (mines up at 59 inches... but I'm tall and I also had to accommodate a smoker oven under the pizza oven). A couple of weeks ago, someone on this forum conducted a poll on the height... seemed that the preferred height works out to be somewhere around 60% of the height of the person that will be the primary cooker. Since you're the one building it, assume that your wife won't be using it nearly as much, so build it for your height.. There was also some discussion on building it up as least as high as your elbow (search on “hearth height” on this forum)

Given all that, I would step back from the wooden wall a few inches and cut a shallow trench parallel to the wall to pour a concrete footer. Then figure the distance up the slope where your oven and extra insulation around it would extend to…probably about five feet up the slope for a Casa 90c...then dig another shallow trench across the slope for an upper footer. With your slope, the upper footer would be about 9 inches higher than the bottom footer. I would then build a short 4" wall on the upper footer and a 13" inch tall wall on the lower footer (i.e, up to the height of the upper footer.) Easier yet would be to pour a concrete-formed wall that would tie upper footer and lower footer together with side walls about 4 inches thick…the concrete pour would be the front wall (just behind the wood wall) and side walls extending back up to upper footer, All the concrete walls should have a little bit of reinforcing wire (or even 2x4 fence wire in a pinch) If you do a poured wall, you could line the form with plastic sheeting that would stay in place on the upper side and underneath everything once you knocked off the forms..

FIll the space with an insulation (I prefer vermiculite concrete but do what works for you) between the front wall, side walls and back footer. The ground will suck too much heat out of your oven otherwise. The hearth would be placed on top of the insulation just above the level of the upper footer and the bulk of the oven would be back over the slope.... actually I would counter-lever a hearth landing (shelf) over the wooden wall…. You don’t want it sticking out into the patio space because that’s probably at a premium given your slope.

Materials to do a concrete poured wall with proper footers should run less than $100…given everything you’re going to spend on a oven, that’s just a few percent of the overall cost. You really wont need French drains around the upper side of the oven… the four or five foot width of it presents such a small area for water pressure to hit on to cause a problem… leaving plastic sheeting in place on the upper side of the upper footer and under the insulation layer just gives extra peace of mind.