Oh what have I let myself in for....

[aph257]

the only way i see it being done, and i mean properly, is take up T&G, cut/remove blocks put joists in supported at mid point, re-lay T&G.

 

[mikethetile]

Ruth

if you rip up the T&G floorboards and add extra joists theres no need to replace the T&G you can lay 18mm wbp ply straight to the joists

is this a fitted kitchen and your worried about having to take out and refit the kitchen

 

[Ruth]

Thanks Mike and Paul. Ah, I had thought I'd have to re-lay the T&G (I know a virtually impossible task without damgaging the boards), but if I could board straight onto the joists that would be more straightforward. So if I doubled the number of joists (ie every 200mm) would it still make sense to add noggins? Would 18mm ply still be thick enough (would be preferable, 23mm must be impossibly heavy!)? If you think 18mm isn't thick enough, would it be possible to lay say 12mm ply first, then over-lay a second layer, say the 18mm? No worries about the the kitchen units, they are all coming out anyway.

Mike, when you say the ends of the joists have to be captive, do you mean they must not only sit on a supporting structure, but be held down by masonry to prevent the ends rising when a weight is placed in the middle?

 

[mikethetile]

yes Ruth

or in a joist hanger fixed to the wall, as long as they cant lift at the ends when you put downward pressure in the middle

if you cut and replace the blocks on the support walls theres no need to noggin as well but you will need noggins to support the ends of the boards


23 mm wbp would be better than 18mm as you dont have the additional support of the T&G