Well, cheers for all the replies and comments - I'm somewhat of a
newbie on this group but, as I've got an entire house (well, flat) to
renovate, I can see me being quite a regular here! :-)

I agree on the SDS front - think I'll have to find some room in the
'renovation budget' for one of those... been meaning to get one for a
while now anyway.

I would expect the simplest way would be one substantial beam
(probably a RSJ) right through the middle of the loft

Unfortunately (I didn't show this on any of the plans for simplicity)
there's actually a bay window at the front of the house which may cause
some problems for supporting an RSJ - not sure - another structural
engineer question I think...

If you wanted to clear the space in the loft you would need to do
away
with those king posts.

Yeah - this would certainly be the preferred option since it would give
me over 600 square feet of open loft space... which would be nice. The
structural engineer (SE) suggested reinforcing the principal rafters
with steel 'U' shaped strips, which may provide enough support to
remove the cross-struts. Unfortunately he didn't want to guarantee
this without modelling it though - same goes for the king post (see SE
comments below)...

That would rely on the existing stucture to carry the load. You would
need your structural engineer to do some calcs to see if it is up to
it.
It also depends a little on wether we are talking about adding
storage
space, or actually doing a complete "floor" that would be suitable
for a
loft conversion.

Yeah - again, SE territory as you say. Initially the plan was to just
do the loft out for storage (we were going to get a full conversion
done until we found every quote was coming back at =A320k+ - plus, with
it being a flat, it would mean additional fire protection between the
ground and first floor, which would be a major pain in the arse). So
the plan now is to kit it out for storage initially with a view to
turning it into some sort of cinema / music / toy room later down the
line. So it would certainly make sense getting the floor sorted now...
it also gives me something to do while waiting for planning permission
etc. for some of our other projects. :-)

[SE] Let us know what he says - it will be interesting to get his
take on it.

Well, here goes!

Basically there's 3 stages to the whole project...

1=2E Fit the loft hatch
The SE was confident the loft hatch could be fitted into the existing
ceiling joists without compromising structural stability providing the
supporting joists at either end are doubled up.

2=2E Fitting a 'floor area' for storage
He was happy with a '1/6' section of the loft being devoted to storage
however a new floor would be required in this area - this would need to
be held in the wall by joist hangers on one side and rest on one of the
30' beams on the other... er, like this:-
http://www.pciq.co.uk/pics/storage.gif
It would require some structural calcs to ensure the beam can handle
the weight, but nothing too major - he reckoned around =A3100-=A3150 for
his time, and this would include specifying materials, design etc.

3=2E Full 'shell' conversion
Finally, he quoted around =A3350-400 to model a full shell conversion -
this would include removing all king posts and struts and putting a
brand new floor in place. He's fairly certain this would involve a
fair bit of steel work, but it would all be dependant on the computer
modelling to work out the cheapest / easiest way of doing things.

Just waiting to get the finalised quotes off him before proceeding -
think we might just have to go for option 2 for the moment since, in
the scheme of things, option 3 will be out of budget for now... at
least until we get the rest of the flat finished. Not sure yet...
Anyway, what do people know about soil pipes? :-)

Andy