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The Basics of Bathroom Plumbing

The Basics of Bathroom Plumbing

When planning any bathroom, a good place to start is with its individual mechanical systems. This means understanding and planning for the room’s major plumbing, electrical, and heating/cooling/ventilation requirements. In renovation work, existing deficiencies-a system that doesn’t meet code or an inadequate dimension-often have to be corrected, a potentially costly and unforeseen addition to the project. Knowing how the various systems go together, as well as the requirements of applicable building codes, is an essential part of the planning process.

I’ve often heard it said that stacking bathrooms one above the other or arranging baths and/or kitchens so that they can take advantage of a “wet wall” is desirable because it minimizes plumbing runs and the number of drains and vents required in the system. In theory this makes sense, and in commercial multifloor construction that is often exactly what designers and architects do. But in the real world of residential construction, sometimes this happens and sometimes it doesn’t. Sure, putting a second-floor bathroom directly above the first-floor bath and configuring them identically is more economical than a more random placement, but it’s not that much more economical and generally not worth the sacrifice in planning flexibility. Since plastic ABS (acrylonitrile butadiene styrene) and PVC (polyvinyl chloride) pipe (the materials most commonly used in most residential DWV systems) are cheap and install quickly, positioning the bathrooms advantageously to one another is less important in the long run than making sure that they are properly situated in the house.

Bringing water into the house, delivering it where it is needed, and then removing it is the responsibility of the plumbing system. While plumbing a whole house is outside the scope, knowing enough about plumbing systems to know when you need help and when you can go it alone can save a lot of aggravation and installation time. And new fixtures and features in today’s bathrooms, like multiple showerheads and jetted tubs, make planning an adequate system essential for proper fixture performance. A tub that takes forever to fill or an anemic shower system that dribbles when more than one showerhead is turned on won’t win many repeat customers.

Essentially, residential plumbing consists of two basic subsystems: the water supply system and the drain/waste/vent (DWV) system. The water supply system must have adequate pressure to deliver proper water flow to each fixture, particularly when more than one fixture is used simultaneously. The DWV system doesn’t rely on pressure to remove fluids, so pipe diameters must be large in order to allow gravity and atmospheric pressure to work.…