In message , John
Rumm writes
snips.

Two things spring to mind. Firstly doing this will probably need
building regulations approval (and hence submission of a building
notice etc). The BCO may want to see calculations to show the new floor
will meet the required deflection limits etc.

Secondly, it is usual to insert new beams with a spacer under their
ends so that they keep clear of the existing ceiling. This saves and
chance of damaging the ceiling when they deflect. In your case however
you may not want to do this since it would take the floor level up a
bit from the rest of the joists. You may be able to get away slightly
less deep (but perhaps wider) joists - although you are not starting
with much.

Having lived in a bungalow converted to have dormer bedrooms I can
confirm that secondary joists not fixed to the originals causes problems
with the existing ceiling. In our case this was limited to the plaster
skin popping off the nail heads but still a nuisance.

regards



--
Tim Lamb