Raising previous concrete garage floor to meet concrete floor level

CattyUk

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Doozergirl

What exactly is the problem?   Do you have damp issues?  

There's nothing wrong with raising the floor level using wood. The drop into a garage is often 100mm because that is what was needed to meet building regulations in case of a flammable spillage in the garage.  

Doozergirl

You put a damp proof membrane down and then place the new wood 'joists' on it, along with some nice solid insulation to help keep it warm.  Then board over.    You don't need a 150mm gap.  

Virtually every upstairs of every house in this country has a bathroom on a wooden floor, it shouldn't be a problem on the ground floor either, but marine ply laid will help the floor withstand spillages.  Spillages shouldn't be creating rot though, it sounds like more leaking.  

If you've got leaks in a bathroom then you've got a quality of fitting problem, not a damp problem.  

Laying concrete can push damp up walls where there was no issue before and breach a wall's original DPC.  It's also going to utterly ruin the decor of the rooms that need raising, plus more damage where you need to gain access.   It's expensive and unnecessary.