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Route Planning

Because my quick estimating system works so well, I don't have to plan the exact repiping routes until after I get the job. When the time comes, however, route planning is the most important aspect of the work. On repipes, I find that branch routing works much better than home-run routing because there are fewer lines to run. I carefully consider several different route options, then choose the one that minimizes damage to finish walls, ceilings, and floors. In southern California, where the original plumbing is usually installed in the slabs of homes without basements, repiping generally involves leaving the old pipes in the slabs and running the new pipes in the ceilings. In a one-story house, this can mean that most of the work takes place in the attic and very little damage is done to drywall. One drawback to running pipes in an attic is that cold water lines are often heated up during hot weather, resulting in tap waits for cold water. Most times, however, homeowners will choose this over other more expensive and disruptive options. Of course, plumbers in cold areas of the country will have to worry about the opposite problem - pipes freezing if they are installed outside of heated spaces. Many houses in those areas, however, have the advantage of a full basement or insulated crawlspace. In general, routing water supply lines on a repipe job involves a few rules of thumb and a healthy dose of common sense. On most jobs, work starts at the front service. Often, I leave the existing pressure regulator and ball valve, and run a new main line to the water heater. From there, most houses require two primary runs, one heading toward any full bathrooms and another heading toward the kitchen. Secondary branch lines can usually pick up half-baths, hose bibbs, mop sinks, washing machines, dishwashers, and ice makers. Running primary lines through ceiling joist bays usually works best for long runs. Drywall cutouts need to be spaced to accommodate PEX hangers, which should be installed every 2 to 3 feet on horizontal runs and every 4 to 5 feet on vertical runs. When running secondary lines beyond ceiling bays or attic space, the best route is the one with the fewest cutouts and drillouts. For example, choosing a ceiling bay that delivers a primary run as close as possible to a bathroom branch can reduce the number of joists that have to be drilled. I've seen lots of jobs where the plumbers spend too much time going over alternatives or where lots of second-guessing goes on after work has actually begun. The fact is that there's almost always more than one good way to route the many runs on a job. What's more important is making sure nothing critical is overlooked, such as structural limitations that are strictly defined in the code. Sometimes, it's necessary to make a few exploratory cuts early on to verify that particular beams can be drilled through. What material a beam is made from, as well as manufacturer specs, can determine routing decisions by forbidding certain drillouts. For most cases, code rules for drilling holes are clearly defined (Figure 3).

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Figure 3.

The plumbers in the author's company follow basic rules for drilling holes in floor joists (top). With wood I-joists (middle) and other types of engineered lumber, it's best to consult the manufacturer's literature. The example provided above is courtesy of Trus Joist MacMillan. Once a route is planned, it's easy to size piping. After determining the incoming water pressure, a chart in the plumbing code specifically defines how many fixtures can be run off of each size of piping. If I haven't had to replace the pressure regulators, I always check them to make sure they're working properly. Typically, water pressure on a water supply system should be regulated at around 65 psi.