Glenn Herbert

The question is what materials are needed, and how much. The OP doesn't want to miss something that is needed but he hasn't thought of.

Sketch of concepts above:

The simplest and probably most effective clerestory glazing concept would probably be to run solid new roof up to the existing wall, and replace the existing wall sheathing/siding above it with glass.

Deepest light penetration, glass somewhat sheltered from direct summer sun but exposed to winter sun, glass-to-new-roof transition somewhat protected from water...

With the angled face to the south, the greenhouse-like shelf makes sense. An all-glass roof sloped to directly catch maximum summer sun concerns me. I would bet a summer white canvas covering would happen to reduce the bake oven effect. I am not enamored of the largely glass exterior, but it does have the attraction of a novel way to protect lower walls from splashback. Ash's berm-shed-like timber bracing looks cool, though I think a far more modest version of it would be fully sufficient to stabilize this structure which has no lateral forces on it aside from wind and doors opening and closing.

I note the cob layer inside the glass facing in a detail; would this cob be in danger of trapping water vapor at the cold face and getting waterlogged? I think using the exterior glass skirt as splash barrier, but leaving air circulation space (an inch or so) behind it and letting the cob breathe might work better. Also, the principle of interior mass insulated from the outside seems to be turned upside down here - granted the amount of cob is not really enough to call "mass". I could see reducing the overhang under the shelf and making an actual mass thickness of cob on the interior, with an insulating layer and perhaps more cob behind the glass on the exterior. Maybe this sandwich could be made visible at a corner or end as a demonstration.

For the roof, the relatively low slope does make glass attractive for waterproofing, but it also necessitates high-tech sealants between panes to avoid leaks. I agree with the notion of increasing light into the depths of the garage space. I wonder if there could be a solid roof with a clerestory strip at the upper end abutting the existing wall. That would allow insulation on most of the roof to reduce massive winter heat loss and summer heat gain, yet still light the interior.

So if there is electricity in exterior walls, it would be in conduit... Does any wiring go from exterior walls through interior walls? Would any of it be disturbed by tearing out the walls? Rerouting would probably be a pain or unsightly or both...

Concrete floor slab sounds easy enough to relocate walls on, maybe just patch a few screw holes and refinish. You say "timber frame"; we would call what you have a stud wall rather than a timber frame. Timber implies larger pieces of wood.

It would be more material-efficient, but it would also require much more precise load calculations to keep the arch in exact relationship to the force distribution. The thick earthbags will stand up as long as the actual line of force falls within the 20" thickness you show, which is pretty easy to get intuitively. A thin arch which does not have great bending strength must follow the line of force or it will fail. If it is well reinforced, it can tolerate some deviation from ideal. An arch with equal total thickness of material needs to be a catenary shape for proper load distribution. If the thickness is not uniform (such as bermed sidewalls), calculations can be very complex. Antoni Gaudi was one of the greatest users of organic arch forms.

Running conduit in the new walls sounds like the right choice; I think PVC would be best to avoid ever having corrosion issues. Obviously the less conduit you have to deal with, the better, so a good efficient layout before you start building will be important. What are exterior walls, and how is electricity running in them now (if any)? Where is the main electrical panel?

You mention using concrete block for the lower courses of the new walls... while a good plan for exterior walls, I would question the need for it on interior walls. If you need such serious moisture protection, I would be concerned for your furniture and rugs. What is the existing floor made of? The new walls will be going on what is now the middle of rooms in some cases. I presume the floor is on grade without a basement or crawl space. If you want a moisture barrier, I would think a layer of it on the floor before you start building the walls would suffice. How will the vertical poles for the wattle and daub be secured at the base? A base plate?

Or is it a dribble of creosote? Either way, not a good thing...

A 60cm square steel base plate would give fast heat due to conductivity, plus considerable mass. Good plan.

I would advise a bell rather than piped mass; there is no reason a bell can't have thick sides and top giving significant mass. My bell has sides of 2 1/2" brick plus 6" of cob, takes hours to warm through, but keeps warm for 24 hours. The steel access plate in the side gives instant heat.

A batch box combustion core would be better if you can't put it where you will easily tend it for a couple of hours a day, and for more heat output for a given size of system (likely important in a good sized old house). A J-tube core is decidedly easier to build for a beginner. If you are mechanically inclined and fairly handy, go for a batch box.

A rule of thumb for bench-style RMHs is that if you could safely install a king-size waterbed, you can build an RMH in the same spot. If you do a vertical masonry bell as mass, that will be more concentrated and require a dedicated footing and posts/pier(s) down to the basement. Code requires continuous masonry all the way to the ground, but if you are not bound by that, steel posts and a good thick reinforced concrete footing will work fine.

Old (and new) radiators were placed on exterior walls to make heating more even, at the cost of wasting a lot of heat warming the exterior wall. The radiant warmth of an RMH will give good comfort from the center of the house. It might work well to remove part of a wall between rooms and put the bell mass in the gap, directly warming both sides. Photos of the areas involved would let us help assess the feasibility of particular locations and layouts. The location of major interior beams in the basement would also be important information.