First time bathroom renovators often overlook or incorrectly record the most important measurement when planning to install a new toilet. That measurement is the toilet rough in. The toilet rough in refers to both the area where the waste outlet hole was placed to sit beneath the toilet, as well as the toilet rough in measurement. This is the measurement that determines which toilets will or will not work in the space.

This can be confusing as the logical assumption would be to purchase a toilet with a base of similar size to the original toilet, but it's actually the distance between the drainage hole and the back of the toilet that's required. To accurately obtain this dimension, start at the back of the toilet and measure the distance to the center of the waste outlet hole on the underside of the bowl. Usually, this toilet rough in measurement is 12 inches (30.5 cm), but manufacturers also offer toilets to accommodate 10 inch (25.4 cm) and 14 inch (35.6 cm) toilet rough in measurements that may occur due to construction mistakes or awkward floor joist placement.

Purchased toilets must be compatible with the rough in measurement, or else the toilet won’t match the drainage pipe location. On occasion, renovations will require the toilet rough in be moved, which means the drainage hole must be relocated to another area of the bathroom. If no toilet currently exists in the space, the rough in can be identified by looking for a drainage hole with an external “lip”. This lip is called the flange, and it will have a wax ring surrounding it.

Installing a toilet over an existing rough in is relatively simple, but relocating the rough in area can be tricky, and should only be handled by someone with prior plumbing knowledge. To do this, the floor must opened up, and if the bathroom is at basement level, this will entail busting through the concrete. Also, considerations must be made regarding the water line, drainage line, and pipes. Redirecting these could result in plumbing flow problems, plus there are specific plumbing codes that must be followed.

Simply replacing the toilet does not warrant any sort of notification, but any time pipes are altered, permits may be required. It’s essential to follow the plumbing and building code exactly, because a permit may also lead to a required inspection and approval. This is necessary because any time pipes are altered, it could likely impact the balance between drain and vent segments.