"N. Thornton" wrote
| Let me take a wild tack here, something I've always wondered.
| Usable area depends on available height, which is often deficient
| or at best tight. If one added a foot onto the brick wall height
| it would make a great difference to what one could do up
| there. So... here goes: is it possible to jack up the entire
| roof structure - or perhaps one side at a time - and build
| up the brickwork course by course?

It is possible to jack up the entire roof structure (NOT one side at a time,
or it will go squint) and rebuild underneath and this is not unusual in
renovation work. However the costs and difficulty in doing this are only
worthwhile where it would be extremely expensive or impractical to rebuilt
the roof. You might not get any extra height, because the joists holding up
the ceiling of the storey below are often an integral part of the roof
structure, preventing spreading, so you couldn't remove them. You would also
have the difficulty of matching the existing wall finish or having a band of
different colour wall all round the house. And because you would be building
above the existing ridge line you would need full planning permission.

For a loft conversion, the structural work involved in modifying the roof
mean that it's as easy to rebuild the roof with alterations as it would be
to lift it; if it can't be rebuilt it probably won't be much use after
lifting.

What can sometimes be done, where the ceilign joists aren't part of the roof
structure or their function can be replaced, is drop the ceiling level in
the first floor bedrooms a couple of ft to gain extra headroom in the loft.

Owain