Is there a norm that the kitchen is lower than the living room?

The general practice is: 3mm-5mm is enough. The floor of the kitchen or bathroom has a slope from the door to the floor drain, so it is a little different from the living room.

If there are enough bad ones, use foam bricks and cement concrete. The weight is relatively light, and most of the partition walls made now are made of this material, 30 by 50 pieces.

The bathroom and kitchen should be low, and the bathroom should be the lowest, remember.

This doesn't need to be much lower, and it usually makes a difference of one centimeter. But I don't feel necessary. Some masters will improve a little bit when they paste tiles, because the distance is large, so they can't feel the slope, and I personally prefer this kind of one. So that there is no drop in the place of the interface of the door.

The ceiling of the aisle can be higher than the living room, which does not affect it, but the most important thing is to evaluate the distance between your aisle and the living room, as well as the overall pattern. There are also aisles that should be lit, if they are not too high, and they are not halls next to them, so they will look weird.