Our 1930's 45 degree bay fronted semi has been suffering from a sagging bay
since we bought it in May (well, its been suffering from it for longer than
that it appears!). This was the cause of some cladding to pop off a while
back (and a posting about what to stick it back on with).

Firstly an explanation of the symptoms:

Upstairs small (2mm?) crack showing in plaster at edge of the bay. After
removing plaster can see a 1cm gap at the top (window ledge height) going to
0cm at the bottom. This had obviously been replastered in the past.

Downstairs, the inside window ledge dips down slightly (enough to notice by
eye) at back of the corners where the large wooden supports go. Window sill
is otherwise flat and level.

Cladding (which is fitted against bottom of external window sill) popped off
in 1 place. Suspect that its happened before on other corner due to slight
differing of mortar colour.


Now, after taking a good look at the area exposed by the popped cladding I
believe I have now sourced the cause of the sagging. The underside of the
exterior window sill is very rotten. I can very easily push something into
it. The front part (which extends past the cladding) is okay, but gets
worse as you get further back towards the brickwork. From what I can see,
the bit exterior wooden sill (part of the whole window frame) sits directly
on the front wall of the cavity. If this sill has rotten, then the sill is
slowly being pressed/compacted into the brickwork as the wood rots further.

Does this sound like a reasonable explanation? If so, would replacing the
whole window be a suitable solution? I'm not thinking about curing the
slight drop in the upper bay as this appears to be stable - and once the
source of the dropping has been solved, it shouldn't move any further. In
the year we've been there, we've not noticed any further dropping - the
popped off cladding was just leaning off since we got it - so its not
suddenly popped that off.

I can't see that replacing the sill is going to be easy because its part of
the window frame, and would probably need the windows to be removed anyway
to get access. Removing windows means propping up the bay... whilst that's
being done, seems easy to put in new windows!

We had hoped on replacing the windows (old wooden frames with poor aluminium
double glazing) at some point - but if the structure of the house pretty
much depends on the windows being replaced, then it may be more urgent and
important to get it done sooner rather than later.

Any thoughts?

Thanks

David