When you install a new toilet, or replace an old toilet, the toilet has to attach to a flange. This flange is known as a closet flange, which funnels the water into the drain pipe below the floor. When the flange is installed, it is usually mounted to the sub-floor, and the finished floor is built up around it. When the toilet is installed, it needs for 1/2" of that toilet flange to be above floor level. Toilet flange extenders are used to give additional height to the closet flange if there is not 1/2" of clearance.
A closet flange extender resembles a large gasket, and is similar in diameter to the exposed end of the toilet flange itself. When you place the flange extender over the closet flange, the closet bolts should easily be threaded through the appropriate holes. Flange extensions come in 1/4", 1/2", and 3/4" sizes. If you install a flange extension and find that there is still a need for additional height, additional flanges may be stacked to achieve the proper height.
If you are installing new flooring, removing your toilet and using flange extenders can give you a more finished appearance than trimming the floor around the toilet. It is important that you check your local building codes before installing toilet flange extensions, as some areas do not permit their use. Some homeowners will stack additional wax rings to create height, but this will result in compression and, ultimately, leakage into the floor with every flush. If you don't have 1/2" of flange clearance above the floor, you may end up with costly water damage to the floor and sub-floor.
If the flange is new, check to ensure that it is clean. If you are installing extenders onto an existing closet flange, scrub it well to remove any debris that would compromise a proper seal. Depending on the extenders that you are using, you may or may not need to apply caulking between the closet flange and the extension (or between extensions) for proper sealing. Read the packaging for your flange extenders thoroughly for individual instructions. Once the caulking has dried and the wax ring has been installed, the toilet may be replaced and tested for leaks.
If you are installing toilet flange extenders, try to purchase one extender at the proper height rather than stacking several. T\Although stacking is an acceptable practice, the additional layers allow more opportunity for leakage.
There are closet flange extenders available that do not require any caulking, as they have a self-sealing gasket. These extenders avoid the additional step of caulking between layers, and allow you to move forward with the project without waiting for the silicone to set.
Some use flange extenders to stabilize their toilet if one of the bolts come free of the closet flange itself. There are super flanges that fit over the original flange or partial metal rings that wrap beneath the flange to simplify this repair. Using flange extenders to repair a broken closet flange is not wise and can lead to leakage.