Revisions log for question
How to make the terrace higher by 15 cm? Use piles?
Revision 1
We want to lay 60x120 cm porcelain tiles on our terrace. The manufacturer offers 10mm and 20mm slip-resistant versions. The terrace should be raised by about 15 cm compared to the current one. We will also extend about 1 m beyond the existing area onto the lawn. So far, the terrace is formed by coarse sandstone slabs resting on sand/rubber. I don't know the exact construction and depth, but there have been no cracks or other problems in the last 20 years.
At this point we have 2 applications.
Provider 1 wants to tear down the old terrace and do a completely new structure with a concrete floor slab. At a cost.
Provider 2 wants to concrete the top of the old terrace (plus an extension to the lawn, of course). Also at a cost.
In both cases, the tiles are laid in concrete (or a layer of screed). I'd prefer the option with less material movement and for less cost.
Can't we lay thick 20mm slabs on piles? Clearly we need a foundation for the current lawn area, but a strip foundation would suffice, wouldn't it? What other options are there?