Rear extension over current patio

[ragj195]

I'm thinking of extending the house 4m out from the rear wall. We bought the house a few years ago and there was what seemed like a pretty solid patio about 4 inches below the floor level of the house. We then decked over it. If I build an extension do I need to remove the whole patio and sub base or can I just remove the part of the patio where the foundations will go? Apart from saving lots of time not having to dig it up are there other benefits of having a patio already laid where the extension will be? Could I just damp proof it/insulate it and lay a concrete slab over it?

Thx
Rich

 

[Alastairreid]

You will need a lot more depth than the 100mm you have at present, even if you could lay over the existing slab the insulation is 100mm alone, not to mention screed, dpm, floor covering.

Get the jack hammer out.

 

[ragj195]

Okay thought that might be the case. It may be a good few cm more the 10cm in which case removing the slabs only may be an option? Crazy to think that our lounge/dinner has floorboards under the engineered floor and nothing else. I guess that's why the heating is always on!