Plumbing fixtures such as toilets and sinks are usually mounted on the floor, especially in residential structures. This simplifies installation because strengthened wall supports are not required. If you are mounting urinals or need additional floor space or are using commercial spaces, fixtures are mounted on walls, with much of the plumbing buried within the studs.
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Local and state building authorities develop construction codes based on the needs of their jurisdiction. However, with few exceptions, requirements for closed plumbing fixture supports come from the American National Standards Institute A112.6.1M specifications. These specs, along with other engineering codes, are maintained and distributed by the American Society of Mechanical Engineers, with the goal of promoting the “art, science and practice of multidisciplinary engineering and allied science around the globe.” Using one national standard ensures that all plumbing fixtures maintain the same durability and safety no matter where they are located.
The minimum space requirements for closed plumbing fixture supports depend on the type of wall and carrier, and the number and type of fixtures. A carrier is the fixture support located within the wall studs. Only some of the requirements are listed here. For horizontal adjustable carriers, a single toilet mounted on a metal stud wall requires walls that are at least 4 inches thick, with an interior space of 8.5 inches. The distance from the center of the carrier to the wall on which the toilet is mounted must be at least 5.5 inches. For double mountings in a metal stud wall, the wall thickness remains the same at 4 inches, but the minimum interior space required is 11 inches. The distance from the carrier center to either wall must be 5.5 inches.
For a single toilet with an adjustable carrier in a block wall, the minimum wall thickness is 3 inches. The interior space must measure at least 13.5 inches, with a distance of 8.5 inches from the center of the carrier to the wall holding the toilet. For a double mounting, the minimum wall thickness remains the same, but the interior space must measure 17 inches, with a distance of 8.5 inches from the center to either wall. Measurements for vertical adjustable carriers are generally the same. However, the interior space for a single mount in a metal stud wall must be at least 8 inches, and for a single mount in a block wall, it’s 14 inches.
Sinks and Urinals
For sinks using a basic concealed arm lavatory carrier, the wall thickness must be at least 0.5 inches, with an interior space of 6 inches, and a distance from the center of the carrier to either wall of 3 inches. If the interior requires clearance for a waste pipe, the minimum interior space increases to 7 inches, with a 3-inch measurement from the center to the wall on which the sink is mounted. For urinals using hanger plate carriers, the wall thickness remains the same, but the interior space must measure at least 5 inches, with a 2.5-inch distance from the carrier center to either wall. If the interior requires waste pipe clearance, the interior clearance increases to 6.5 inches, with a distance of 2.5 inches from the center to the wall on which the urinal is mounted.