Kray – I would think that the courtyard turf (be it synthetic or real) would be an owner and/or a builder responsibility. If the turf is within an Exclusive Use courtyard it is not the Owners Corporation’s responsibility. It is the responsibility of the person benefiting from having the exclusive use.
If the apartment is still within the builder warranty period then the Lot Owner would be wise to keep pursuing the builder for a solution. Once the warranty period expires the problem will be the responsibility of the Lot Owner.