Planning for Pipes/Rough-In Plumbing

Planning for Pipes

The location of the water main or the well determines the direction from which the supply pipe will enter the building.  The location of the public sewer or the septic system establishes the approximate route for the building drain.  Once the basic routes for plumbing to enter and exit the building have been established, sleeves may be designed into the foundation to allow for their passage.

The framing of the building must be planned by the designer to accommodate plumbing.  Supply pipes and the smaller diameters of waste and vent pipe will fit within the stud or joist cavities, but special provisions must be made for the large drain pipes.  A toilet drain pipe, for example, must be in a particular location, must have a prescribed slope, and can be difficult to route through framing (particularly from upper floors).  

The clustering of plumbing features around a plumbing wall minimizes the amount of pipe that must be used and can make the plumber's job easier.  It is wise to locate the water heater  centrally so as to deliver hot water to each fixture as quickly as possible and to specify that vents be tied together in the attic to avoid multiple roof penetrations.

Rough-In Plumbing

With slab-on-grade construction, all subfloor piping must be in place before the slab foundation is poured.  In houses with a crawl space, the plumber should complete work in the crawl space before the subfloor sheathing has been installed.  Generally the waste pipes are installed first (because they are the largest and must slope properly to drain).  The plumber will drill holes in framing members for these pipes according to guidelines established by the building codes.  The pipes are then installed and glued together with fittings.  The plumber must also install supports for the pipes.  Supports consist of plastic pipe hangers or a combination of blocking and plumber's tape (a flexible galvanized metal strap with holes for fasteners).  Supply pipes (because they are much smaller and do not rely on gravity) can be routed through the framing without much planning.  Small holes are drilled for pipes to pass through members, and clamps are used to secure pipes running parallel to framing.  A variety of manufactured clips and brackets are used to hold the fixture end of the pipes in place.  Where pipes must pass close to the surface of the framing, a steel nailing plate must be installed on the face of the framing to prevent nails driven during the finish phase of construction from penetrating the pipes.