I am about to refit my bathroom. When I took the side panel off the bath, I found that about 8 of the floorboards are rotten, through water leakage from my over-bath shower. Obviously this has been happening over a period of 10 years or more. The boards run under a wall between the bathroom and kitchen and there is some damp rot on the kitchen side as well (not quite as bad). The problem is that I am in an upstairs flat (maisonette) and the joists run parallel with this wall. Looking at the nail heads on the floorboards, the joist nearest to the wall in the bathroom is 16 inches away and it is the same in the kitchen. So, I thought, the floorboards rest on the wall. Not so, when I poke around with a screwdriver, there is nothing there at all! So I think that there should be a joist which rests on the wall from downstairs, onto which my floorbaords were attached and then, my wall was built directly on top. So, if this is correct, this joist has also rotted - probably about 8 planks, 3 feet in length. I think that I can "splint" this by putting in a piece of joist that will fill the gap and attaching it by two other joists nailed to the sides of the good bits of joist still left. This is all a bit of a guess. DO you think I should be tackling this myself, or should I get a builder involved? Any advice would be gratefully received!