advise on turning loft into computer room and storage

hi i had my loft floor boarded out about 9 years ago had velux window fitted at same time
my hieght from floor to centre of roof 5ft 6in i have ripped my old flooring up and put 6x2 joist in and chipboaded the floor with 18mm chipboard .i was wondering if i could plasterboard the rafters ect to building regs and poss put space saving stair case up to loft instead of useing loft ladders so i can put computer ect up there or do i need to get building control in volved

If you're looking at putting a fixed staircase in and using the roof as habitable space and then look at selling the house with this additional room, then yes... you will need to seek building regulation approval.

There are many things to consider if going down that route, primarily structural and fire prevention. Have a read of the implications on the PP...

http://www.planningportal.gov.uk/permission/commonprojects/loftconversion/

As for the headroom. You mention you have 5ft 6 to the centre (ridge board/apex). If that is the maximum height, then your stair will not achieve the min. headroom required, which is 2m and can be reduced to 1.9m where space is limited. 5ft 6 is approx. 1.65m. You will need a protected staircase (enclosure) from loft to ground floor.

thanks for that iv been looking all week at min heights ect but couldnt find the proper answer
just wont somewhere to put my computer and store stuff
not planning on selling my house and if i did could i just say its just loft storage
just need to now if i could insulat ceiling by leaving a 50mm airgap and plasterboard it to keep loft dry and warm
about the stairs it just makes it easier to get up and down
would i need building regs to install them thanks

If you're converting a loft to habitable accommodation, you will need Building Regulation approval.

As soon as you put a fixed staircase in, the loft becomes habitable thus requiring BR approval. You could argue that by having a temporary staircase (e.g. loft ladder) and board out the loft, etc... could be seen as loft storage, thus not requiring BR approval.

Under BR's, you would look at achieving a min. u-value of 0.18 for roof insulation that follows the pitch line of the roof. This can be achieved with 100mm Celotex between the joists, thus leaving a 50mm air gap, assuming you have 150mm deep joists, then 52.5mm Celotex under the joists with set coast plaster finish. However, anything is better than nothing. Just fill the rafter spacings but maintain the 50mm air gap. Obviously by applying anything to the underside of the rafters will reduce the headroom, which is currently limited.