"swinster" wrote in message
oups.com...
This is an interesting thread. Although I studied engineering and
mechanical structures, I simply can't remember much of it. I want to
look at a loft conversion for our mid terraced house and will need to
consider strengthening the ceiling joists. I have a feeling that this
is a little more straight forward than you problem and has been done
100's of thousands of time across the UK so there should be lots of
info out their.

At the moment all I want to consider is strengthening the
floor/ceiling. The full conversion with stair will come a little later.

At its simplest, lay additional joists the at least the same size as the
ones supporting the floor below (which presumably have the same span)
alongside the ceiling joists - I would actually go up a size as the floor
joists below may now be under specified. They will rest on the wall plates.
Pack them up with plywood plocks about 15mm. This will ensure the ceiling
floats separately to the new loft floor above and doesn't crack when you
hump stuff about.. In addition, cables can be run without drilling (although
that's not the main point) they go over the old and under the new. Fire (and
noise) requirements will be met by laying mineral fibre (rockwool or
similar, not glass fibre) insulation between the joists (80mm plus), nailed
to the joists either side (to prevent gaps) This, with the normal ceiling
below and the eventual flooring (18/24mm t&g chipboard) *should* provide the
30min fire protection that will eventually be needed if a full conversion is
done. Mind you it would then have to be inspected. These are general
opinions based on my loft conversion and are only opinions and should not be
regarded as fact - no liability accepted etc.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)