Kitchen redesign... To match the level of the adjacent living room I need to raise the kitchen concrete floor by 40mm (using 2x18mm ply sheet, plus tiles). At the same time I'd like to prep the cooker installation by laying a gas pipe across the room. This would mean putting a copper tube ON the original concrete floor, UNDER the top sheet of 18mm ply (and tiles on top of that). This seems safe - can't imagine anyone nailing through tiles (except under the kitchen cabinets where it'll be ply) but want to make sure it's compliant before the fitter comes to install the cooker/hob... Anyone see a problem with this?