On Sun, 15 Jan 2012 20:30:10 -0000, Cash wrote:

Ah, I didn't make that clear. It is the internal wooden sills we
would like to keep. One window company has said that they
wouldn't
fit UPVC window frames with existing wooden sills,

Don't use them then. They may have got confused ext v int cills. I
can see that fitting a new fram onto existing external timber would
be interesting. But fitting against existing wooden internal
shouldn't be a problem at all. The snags will be cuased by how easy
it is or isn't to seperate the old frame from the cill. If a window
is removed carefully there should be very little damage to the
internal cill and plaster. A bit of filler will deal with the slight
gap between existing plaster and new frame. A bit of quadrant might
be required along the back edge of the cill but wood filler might be
better depending on the finish, varnished or painted.

Remember to choose a company that's FENSA registered, otherwise you will
have to get the local council involved to issue the necessary paperwork
upon completion to say the job is OK.

FENSA or council BC only mean that the things fitted meet the
regulations nothing to do with the job being OK.

--
Cheers
Dave.