[quote author=Robbo  link=1096062922/15#16 date=1096206472] Joisting is usually one of the lesser problems to overcome, its the fire issues that are the real bug bears. [/quote]

yes, they are a pain in the backside

and three steels thats prpbrably inline with my luck but i hope not

ss

Provided you can get the bearing in the party walls I would do it like this, red squares are steels, brown lines timbers

http://img.photobucket.com/albums/v156/jasonballamy/roof1.bmp

Steel long enough to go front to back would start to become too deep, reducing head room and be hard to get hold of, most steel stockholders keep 6.0m lengths. Was involved with a mansard roof where the steels went between party walls and were in two pieces joined with plates, made them easier to install and handle, pulled then up with a barrow hoist and manhandled into place.

Where are you measuring the 2.34m height?

Jason

Reading your posts again you say  the rafters 3x1 and mention the word truss.

How old is the house, does it have a traditional cut roof or modern trusses, perhaps a general pic of the loft may clear things up.

Jason

Are the existing joists running in the same direction as the red lines that indicates the steels in your original drawing? if so I posted thinking they ran the other way.
Now this gives you 3.6 to the internal divideing wall right? So could you not then use 8x2 at 4.2mtr  champfered at one end (the pitch of the roof angle)and tucked in tight over the wall plate and nailed to the bottom of the rafters, the other end would overhang the central wall by.6 of a mtr. If you then repeated this from the other side but placing the new joist the opposite side of the corresponding rafter on that side the middle could be bolted together as you have a now 1.2mtr of double joist, may possibly need to add a corse of brick to the central wall for levels.
What you have in your loft is not a conventional factory type made fink truss but more a kind of mish mash of hangers, purlin struts and collar ties all serving a specific purpose. You obviously need to remove theese so my opinion is that you will need to install two further purlins to compensate for all theese supports being removed.. excepting the original purlins. One problem that springs to mind is the need for a top hung velux window to act as a means of escape which I think needs to be around 1.5 mtr from the finished floor level and if there is a purlin there you may have a problem.
Also are you aware you will need to double board the second floor ceilings to half hour fire regs, possibly fire doors and self closers also and a wired integrated  smoke alarm system on all three floors, a minimum headroom for the stairs all enclosed to half hour fire with doors top and bottom, the list goes on.... lofts are a pain really when you consider the legalities of doing it by the book, as often as not you are better off building an extension if this option is open to you as once the consideration of what space will be lost putting in a stairway compared to what will be gained may be a false economy in the bigger scheme of things when it comes to both practicallity and adding value to the property.... though having said that lofts are a great place to throw the kids up into when they are driving you nuts.

i think ill go the unnofficial route and board it out
what can be done without it being classed as a bedroom? i take it its a matter of stairs?

pain in the ass with all the regs

oh and the joists are alot firmer now ive done a bit more boarding- think the 4*2 with 2*2 across will be up to the job?

cheers

ss

I think the hobby room route is the best option, by the time the floor was strengthened and the slopes insulated you would have very little head room to make a worthwhile room.

Get a good quality pull down ladder to make access safe & easy without the loss of floor area that propper stairs would take up.

Jason

cheers everyone
looks like ill just board it out lol!
25k is not soo bad but its also no worth it for what we would get/ hastle we would have getting it done

cheers

ss

that is not true about trimming floor joists on the angle it is perfectly acceptable for a new build where those are acting as ceiling ties and not floor joists as in a loft conversion.Imagine this your new 8" floor joists meet up against your existing 4" rafters and you cut them off on the angle you are reducing them to about 65-100mm across their bearing on the wall plate would you be happy with 4" floor joists. Do it and see what building control have to say about it I am presently working on a job where the architect specified to do that and building control turned it down.The dormer construction is not the only purpose of a ridge steel the steel is there to also take the weight of the front roof, as ther are no longer any corresponding common rafters on the dormer side of the roof. Admittedly this can be acheived with timber but for a 5.59m span you would need the equiveelant of a 10x8 softwood beem and usually you dont have 10" headromm to spare in your average loft conversion