I decided a while ago to renovate (rather than replace) the sash windows
on my victorian house.[1]

One of the first issues I cam across was the size of the (vertical) gaps
between the frames and the brickwork in many cases: Far too wide
(~15mm) for a normal dollop of sealant. Presumably these were
originally sealed with a fillet of mortar or something.

Anyway I decided that these would be best covered with a strip of
moulding and have been painting the mouldings off the job to make it
easier. Now they're ready, the question arises of wehther I should just
put these on and seal up or whether the fairly substantial void behind
them (15mm wide but a couple of inches deep to sound but weathered
timber)would benefit from judicious application of expanding foam, as
normally used to fix windows etc these days.

I know PVCu box sash windows shouldn't be fixed with foam as the
expansion can distort them, but what about timber? Any views or
experience chaps?

[1] On the topic of refurbishing windows, I took a trip to Reddiseals,
who aren't far from me. Spent a lot more time there than I had planned
chatting with their man who clearly knows his stuff. Spent a bucket of
money too(!) but more importantly changed the approach. I'm sure there
are other good places, but their stock is pretty impressive and advice
is well informed. No connection, etc, but I'm sure I'll be over there
again before too long.
What amazes me, though, is why at least some of the seals and bits
aren't stocked by the sheds. Surely there must be plenty of demand.