M
Monkey Wrench
another way of constructing the raised area would be to rip some 18 mm ply in to strips equal to joists ( about 8 inch ) , screw them each side of the joist to the new height and then insert smaller packers between the ply on top of joists. Hire a laser level or if you have large normal level then this will do.
note: get your ply wood from bnq and get them to rip it down, they also have local price match policy and will beat rivals by 10%.
also, use plenty of screws!
Thank you charlie1, when you say "equal to the joists" (about 8 inch), I assume you mean the depth of the joist ! Should these also be spaced at 600mm ?
What do you mean by "get B&Q to rip it down" ?
Thanks again.