I am going to replace the chipboard floor in my bathroom withh 18mm wbp ply. The bathroom size is 9ft 8inch by 4ft 10inch the joist, run down the longer dimension. What would be the best way to lay the ply, down the longer length following the joist or across the joists ( the 4ft 10inch measurement). Another question is were the walls are there is only about 1inch of joist to screw the ply down to. So my idea to give the ply a bit more to rest is to screw a piece of 4x2 down the length of the joists, is this ok. I would love to be able to get the ply under the footplate of the one partition wall that seperates bathroom from bedroom but i cant see an easy way to do it. So i came up with the 4x2 thing.