The National Plumbing Codes Handbook compiles all the relevant plumbing rules and regulations for professionals. It is up to the municipal code enforcement officer to inspect and sign off on any new construction or remodeling. If the plumbing is not up to code, the building is considered unfit for use until it is corrected. The code for a bathtub drain is 1 1/2 inches in diameter.
Soaking away troubles in a warm bath is a luxury that became available to the common people with the development of indoor plumbing. As more people gained running water in their homes, disposing of it became as important as providing it. Drains soon became standardized so plumbers could complete a home safely, quickly and inexpensively.
The drain is often covered by a fine mesh screen with keeps most debris from sliding down into the pipes. Over time the drain may become clogged with soap, long hair, body oil and other material that combine together to make an impenetrable mass. A small commercial "snake" made from plastic or metal can be run into the drain after the mesh is removed to address the clog. If this doesn't work, various drain cleaners are available for pouring down the drain to dissolve the clog.
Other, specialty tubs also have the 1 1/2 inch drain code. This includes hot tubs, whirlpools and soaking tubs. Water generally does not have to drain quickly from a tub, so there is no need for a larger drain. In comparison, the drain for a kitchen sink is a standard 3 1/2-inch opening that feeds into a 1 1/2-inch tailpiece. All drains must be vented and sloped according to code.
Standalone showers need to drain much more quickly than a tub to prevent an overflow of water. Shower drains are standardized by code as 3 1/4-inch drains, which carry water away much faster. If the shower is combined with a tub, the code for the tub drain applies. The idea is that the shower water can back up several inches into the tub without causing damage.
- National Plumbing Codes Handbook; R. Woodson
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