To self-level or not garage concrete floor with "grooves/waves" to convert to home office

[Alexx]

Hello,

I'm trying to figure out if self-levelling for my garage floor is needed for my home office conversion. There are grooves all the way which some are up to 5mm deep. I'm planning to insulate the concrete floor on top with PIR boards of around 100mm and I was wondering if these grooves will affect them. In theory, they should take some of these grooves into the board once I step on top, but also there are so many and the weight on top may not be enough to make them sit properly now, but maybe later with furniture on top it will and then that will cause some movement on the floor. What do you guys think? My plan is to add a damp proof membrane on top of concrete, 100PIR boards, foil tape in between them or perhaps another DPM sheet to avoid any moisture from above sinking into the boards, 18 or 22mm chipboard on top, then a thin plywood layer as I'm planning to carpet on top. What do you guys think?

[Mr Punter]

You could get rid of any big nibs and brush some building sand or sharp sand over to take out some of the undulation.  DPM lapped up the walls, PIR, polythene then 22mm chipboard with a 15mm expansion gap around.  Will be fine for carpet finish.