David Hearn wrote:
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

In houses of that era the woodwork of the window frame is structural.
Its not unknown for them to collapse, happened to a friend of mine.
Also replacement doubleglazing obviously needs to have this taken into
account e.g with steel reinforcing bars inserted.
This is not obvious though to some cowboy companies.