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Weak downstairs floating floor - add joists to strengthen?

Postby foulkeg » Thu May 15, 2008 3:09 pm

I have a 5 year old house which has a floating floor subsurface. As far as I can tell, it has some solid surface 10cm (ish) down, upon which their is block polystyrene, then a DPM, before 18ply has been laid on top. I'm told this is classic construction nowadays. We have knocked the dining room through to the kitchen creating a larger open space. We have always thought the floor was weak and springy - but having created a much larger space it is now clearly visable when watching someone walk over it.
Now, the wife wants a solid oak floor, which im sure is not suitable to lay directly onto this subsurface (whether glued, nailed or screwed).. so, do I up the ply, and polystyrene and lay a concrete base (very messy, costly etc) or better to up the ply, and lay joists across the floor joined with butresses (cutting the poly where required), then replace my ply with the solid oak flooring (18mm*150), so keeping the existing height of the floor to the skirting etc.

Would I need any planning/permission?
Silly question, but I'm assuming the base under the poly is fit for laying joists on top - is it?
Any further info on suitable joists to use and how to connect with butts (think thats the right term?)
Any better way of doing the job?

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