De or het grondverdieping?

The correct Dutch article is:

de grondverdieping

Rule Words ending in -ing: almost always de. See the rule

How to use grondverdieping

the grondverdiepingde grondverdieping
this grondverdiepingdeze grondverdieping
that grondverdiepingdie grondverdieping
our grondverdiepingonze grondverdieping
your grondverdiepingjouw grondverdieping
every grondverdiepingelke grondverdieping
which grondverdieping?welke grondverdieping?
a big grondverdieping / the big grondverdiepingeen grote grondverdieping, de grote grondverdieping