OK, cheers again for the replies. I spent another day in there
clearing crap out over the weekend (is 28kg of lead piping worth
anything? :-) ). Having hoovered out 11 bags of dust in the area of
the proposed opening, it's all making a lot more sense now, although I
can't say I've ever seen anything like it before! I've taken a couple
more pics to explain...
For starters, here's a scale plan and elevation of the loft (Visio is
really starting to do my head in for this sort of stuff - can anyone
recommend a more 'appropriate' package for plans, elevations and (if
pos) 3D views?):-
http://www.pciq.co.uk/pics/loftplan.gif
http://www.pciq.co.uk/pics/loftelev.gif
(the current and proposed openings can be seen on the right of the plan
- I haven't bothered to show the joists, but needless to say they span
left-to-right (perpendicular to the main beams) and, as mentioned, are
12" apart)
The main beams spanning the full loft are indeed bolted together in two
places, as can be seen he-
http://www.pciq.co.uk/pics/joistbeam.jpg
This is how the principal rafters notch into this main beam:-
http://www.pciq.co.uk/pics/praftbeampur.jpg
This is another view of the ridge board and principal rafters notched
into the king post:-
http://www.pciq.co.uk/pics/ridgekp.jpg
....and this is how the purlins are notched into the principal rafters -
also showing the struts notched into the principal rafters:-
http://www.pciq.co.uk/pics/praftstrtpur.jpg
....and a close up of the latter:-
http://www.pciq.co.uk/pics/strutpraft.jpg
....and the ceiling joists nailed into the main beam:-
http://www.pciq.co.uk/pics/joistbeam2.jpg
So, by my understanding the ceiling joists are simply nailed into the
walls and beams in 6-7' sections, like this:-
http://www.pciq.co.uk/pics/joistevelwl.gif
http://www.pciq.co.uk/pics/joistelevbm.gif
....and if this is the case, no matter how sturdy it currently feels,
there's no way on earth I'm putting any weight on the existing ceiling
joists. New floor it is then! :-)
I would not worry about the existing holes - compared to the task of
adding a new floor, having two holes available is not going to make
much
impact on the total scale of the work. If you need to fix beams to
the
wall these can be hung from a heavy shoe that is bolted to the wall.
I was planning on using joist hangers mortared into the brickwork as
opposed to the 'bolt in' type since I've tried drilling these bricks
and they're like solid steel. Anything to avoid drilling 80 x 10mm (or
whatever) holes would be a bonus! Anyone have any experience of using
these? I was planning on using the Catnic 50x150 ones from Screwfix,
although (as yet) I have no real clue of how many joists I'm putting
in, how far they'll be apart or how big they'll be...
I'm also trying to decide whether to...
1) Simply install the joists in 2 x 3.6m sections bolted together in
the middle (suspended above the existing beams) - spanning the 6.3m
width, that would give a 0.9m overlap for bolting...
OR
2) As above, but notch them into the main beams.
OR
3) Install joist hangers between the main beams and the walls. I.e.
the sections closest to the walls would be supported by the brickwork
and the main beams. The section in the middle would just be supported
by the main beams.
Option 1 would obviously be better for noise since the loft floor would
be totally isolated from the ceiling, however it would add quite a bit
of height to the floor.
Option 2 would save a couple of inches of floor height and would share
the load between the walls and beams, thereby reducing bounce in the
middle (I presume) - however noise isolation wouldn't be as good.
Option 3 would probably be the easiest but places much more load on the
main beams which (although seem to be incredibly sturdy) probably
aren't designed to support a floor.
???
Any other ideas?
A structural engineer is kindly popping 'round to check the situation
out in a couple of hours, so doubtless I'll come back with a whole
different plan... :-)
Cheers again,
Andy