Remove existing floor--extension

[Rhica]

My builders say the existing floor in the kitchen is inadequate and want to dig down and remove it to match the extension. Also say there is no damp proof in this part. For this, to reconnect the downstairs loo (not part of the extension but requires digging and relaying pipework) and extending the roof (flat roof) over half of garage they want 10k. Does this sound about right? What would be the consequences of not doing the floor. Already paid 7k over original quote

If there’s no dpm (damp proof membrane) the consequence of not doing the work to install one in a concrete floor (what it looks like from the photos) is a damp floor.