Correct Flange Placement
The best placement for the toilet flange is with the underside of the flange resting directly on top of the finished floor. Some installations have the underside of the flange slightly below floor level, which can also work. However, always consult local plumbing codes to make sure this is permissible, or whether the flange should always be placed with its underside on top of the finished floor.
A flange below the finished floor may compromise the water-proof seal, which is created by the wax ring. The wax ring goes between the toilet base and the flange, and if the distance between the two is greater than the height of the ring, water will leak from between the flange and toilet after every flush. In addition, sewer gases will leak into the room.
Raising the Flange
A popular way to raise the flange is by installing flange extenders, also called flange extension rings. This item is available at hardware stores, home improvement stores, online and at plumbing outlets. You can also stack two wax rings on top of the flange or use a "jumbo" ring. Also, because the distance between the flange and the toilet base is now greater, you may also need to install longer flange bolts to securely anchor the toilet.
Reasons for High Floors
Usually, a flange needs to be raised due to new tiles on the bathroom floor. When this is properly done, the toilet is removed from the flange and the tiles are installed up to the flange perimeter. In-floor radient heating can also raise the level of the finished floor.