A best practice is to install the toilet flange on top of the finished floor. If you install the toilet flange flush with the finished floor, or even below the finished floor, leak paths will form, because the flange won't be at the correct height to accept the horn at the bottom of the toilet.
In a typical toilet installation, the floor flange that sits inside the drain opening below the toilet should be positioned so that its bottom surface rests flush against the finished floor or no more than 1/4 inch above or below the floor.
The toilet flange needs to be on top of the finished floor. Meaning the bottom edge of the flange needs to be on the same plane as the toilet. So if your toilet sits on the tile, the flange needs to be on top of the tile too. The spacing of the toilet exit "horn" and sealing surface is designed for this height.
With the toilet removed, you can see the toilet flange and measure its height above the floor. The optimum flange height to aim for is 1/4 inch above the finished floor. This typically allows for almost any type of wax ring to be used and still ensure a good seal.
These flanges install on the outside of either 3" or 4" pipe and can be used without needing access from below. To install an Oatey Cast Iron Closet Flange: Place it over the pipe so the gasket secures to the pipe. Tighten the integrated fasteners to the pipe to secure the closet flange.
When your toilet flange is too high, your toilet may leak water and rock back and forth when used. Both the leaking and the rocking can warp or break the floor. A leaking flange can also rot the subfloor and lead to the accumulation of mildew and mold.
The standard toilet rough-in is 12 inches, but don't assume you have a 12” rough-in without measuring! Some older homes come with 10” or 14” rough-in sizes.
International building codes require that a fixture shall be made watertight where it comes in contact with the wall or floor. One way of making sure this code is adhered to is by caulking around the toilet.
The flange should be fastened to the floor. Dry fit the toilet to make sure it doesn't rock.
If your toilet doesn't sit flush against the floor, it will start moving as you use it. Most often, toilets rock back and forth because of a loose bolt, an uneven floor, or problems with the wax seal that connects your toilet to its drainage system.
The wax ring is located underneath the toilet and is designed to cover and seal the waste pipe and toilet flange. If the wax ring isn't sealed correctly, it can cause wastewater to leak from the bottom. Leaking water can lead to mold around the floor.
A flange that's too big or too small can actually block your milk ducts, reducing the amount of milk you can pump. The wrong flange fit also can lead to engorgement, clogged ducts, milk blisters, and a decrease in your milk supply. Not to mention, it can be pretty painful!
Can you put a new toilet flange over an old one? A standard toilet flange should fit snugly into the outflow pipe and sit level with the subfloor. Installing a new one without first removing the old one will make it impossible to form a seal and keep the toilet bowl bolted securely in place.
Install the New Toilet Flange
If no hardware was provided, use wood screws or cement screws, depending on your subfloor material. Slide the toilet flange bolts into the new flange. Secure them with washers and nuts. There's no need to use an adhesive when installing a gasket-sealed PVC flange.
Low toilet flange is a common problem when installing a new (or in my case thicker mortar base). Unless your toilet is properly mated and sealed to the waste pipe, you may face problems related to sewer gas odor (it's very unhealthy and unpleasant) and/or fluid leaks.
What this means in practical terms is that you should always remove the toilet if you are renovating it, in order to place tiles beneath the toilet on the new bathroom floor. The toilet flange then goes atop after you install tiles for the bathroom flooring.