First of all, I'm very confused by the structure of our 1900's terraced flat so I've taken some pictures to accompany this post which I hope will help!
Basically, I want to fit some (rather substantial) loft ladders however I'm a bit stuck when it comes to locations for them and am left with little alternative but to run them perpendicular to the joists. The opening required for the ladders is 120 x 70cm (47 1/4" x 27 1/2") and the ceiling joists are 12" apart (12" gap that is). The joists are 2 1/2" x 2 1/4" by the way.
Unfortunately this means cutting 3 joists in order to fit them in! (see http://www.pciq.co.uk/pics/newopening.jpg - new hole marked in red). Now that wouldn't bother me too much if it wasn't for two things:-
1. Our ceiling joists appear to be held up by 1x1" bits of wood nailed to 1x4" bits of wood which are somehow attached to the walls (see http://www.pciq.co.uk/pics/joistends.jpg - I'm sure I'm missing something here but see for yourself!)
2. There would appear to be a large king post (11' high) supported by two 2x7" joists held together in the middle somehow which look like they're resting on our ceiling joists (see http://www.pciq.co.uk/pics/kingpost.jpg )
There are NO load bearing walls in our flat (other than the outside walls of course) so can anyone explain the structure of our house?
Anyway, my plan was to basically cut the three joists to create the opening and install some new 2 1/2" x 4" joists to support the cut joists - these would be morticed and screwed together for extra strength. This is much easier explained if you look at this:-
Yellow = new opening Black = ceiling joists Blue = new 2 1/2 x 4" joists Brown = 2x7" joists (spanning 30') Red = King post (11' high)
So basically, the profile of the new joists (shown in blue) would be like this: http://www.pciq.co.uk/pics/profile.gif
My only concern here is that the entire weight of the ceiling, the loft ladder (and people on the loft ladder), the contents of the loft and potentially the king post would be supported by the bits marked 'A' on plan.gif. Should I extend the 'Blue' supports out further (to the next set of joists either way) to spread the load? My only concern is that it would potentially weaken even more joists by morticing into them.
Should I be concerned? Should I employ the services of a structural engineer? Should I sell my loft ladders?
As a side note to all this, does anyone know why we appear to have ready made joist holes in our walls above the ceiling joists? (see http://www.pciq.co.uk/pics/joistholes.jpg and http://www.pciq.co.uk/pics/joisthole.jpg )
Thanks for taking the time to read this epic - I look forward to ANY responses!!