Move external doors to outer leaf of blockwork cavity wall?

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Hi All,

I am struggling to find an answer to this specific query so thought it best to create a new thread.

Background:
Our house is a 1960's detached 2-storey house in Cornwall. The external walls are of cavity construction, with both the inner and outer leaf constructed from concrete block, with yellow blown insulation in the cavity, and painted tyrolean (textured) render to the exterior surface. Both the front and back doors/frames were originally timber and mounted in the internal leaf of the cavity. The front door was changed to upvc probably ~30 years ago, while the back door remains timber. Front door faces SW, so sees a huge amount of rain in winter and sun in summer. The cavity at the bottom of the front door looks to have been crudely filled with concrete, over which was placed a couple of paving slabs that currently butt up to the outside of the upvc door frame. Back door is still timber and is on the side of the house, facing NW. The cavity at the bottom of back door is covered by a row of tiles (red, maybe clay/ceramic?) that butt up to the inside of the timber door frame, which looks like a nightmare to seal even if a new door/frame were swapped-in like-for-like. Both doors leak water on to the floor internally when rain is driven in to them. When I looked at replacing them I noticed that most of the doors I was seeing online are fitted in to the outer leaf of the cavity. This seems much more sensible as it (should) keep all rain outside the house/cavity/blockwork. It also removes the challenge of creating a reliable threshold/cill that currently *should* take rainwater flowing off the door and carry it over the cavity to drain outside the external wall.

Questions:
1. Any specific reasons why I shouldn't move both doors to the outer leaf of blockwork? I'd want to use composite doors/frames.

2. Any recommendations/links for specific advice for doing this job as efficiently as possible?
So far my plan is:
a) Cut vertically down the outer leaf with a big grinder, widening the opening just enough to remove the lumpy tyrolean render and leave a smooth surface on each side. Doing that may open up the cavity on the sides of each door, which is good from my perspective as I can then fit insulated cavity closers and remove what is currently a cold bridge. I would likely leave the render above the door as this is beneath a bellcast that I do not want to disturb, and also I am pretty sure there is a single poured-in-situ concrete lintel spanning the cavity above the entire door opening.
b) I would remove the paving/tiles currently covering the cavity below each doorway and level the surface of the outer leaf using sand/cement (ratio 4-1-1?).
c) I would then remove the existing doors (which so far have protected the house from dust etc from grinding)
d) One thing I need to clarify is how far back from the external face of the walls to position my doors (any tips?), and do I need to leave blockwork visible inside the door frame in order to mount a solid threshold (bottom) and cavity closers (sides). I'd mount the doors as normal with frame-fixings, packers, foam, and either a upvc or solid stone cill beneath.
e) I'd then tidy up the external reveals (which may only be a a couple of centimetres) with fresh tyrolean render.
f) Then I'd tidy up internal reveals inside, skim, paint, etc...

3. Am I making too much of a big deal out of this inner-vs-outer leaf mounting? Maybe I'm wasting my time and mounting new doors on the inner leaf is ok given certain methods?

Any help much appreciated,
Thanks, Rich
 
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