When installing a wall mounted toilet, we are often asked how deep the plumbing void needs to be to incorporate the concealed cistern and hanging fram for the toilet. You require a minimum of 200mm if your soil vent pipe (SVP) needs to exit the room internally and to one side of the toilet. If the SVP exits the room from the rear or the floor then you only need approx 120mm of plumbing void. If there is space above the wall mounted toilet you can use the plumbing void above the concealed toilet cistern to incorporate either shelving or a recessed cabinet for extra storage within the space.
Please click the link below and scroll down to the Wall Mouted Toilets gallery for examples.
http://www.atlasbathrooms.co.uk/galleries/photo-gallery#WallMountedToilets