By Martin S. Harris, Jr.
The following story is true. However, the names have been left out to protect the innocent—and the guilty.
What’s a designer to do when he designs by the book, so to speak, and something fails to work as it should? That was the question posed to me a half-dozen years ago by an architect who had earlier completed a modest addition for a small rural elementary school. Working under state regulations requiring, among other things, low-flow water closets, he had dutifully incorporated a pair of these items in the plans, showing a fairly long (70-foot) branch sewer line connection to carry wastes back to the main sewer line serving the original building. What was the branch line slope? The standard 1/8-inch per foot that the National Standard Plumbing Code requires for 4-inch sanitary waste lines.
Trouble was, the line was plugging up. The architect first found out about it when he received a certified mail nasty-gram from the school board’s lawyers, documenting a six-item chronology of stoppages over the previous year and a half, with related plumber call-charges. The school board was demanding $6,000 as compensation for “poor design.” At that point, this is what we knew for sure:
1. The water closet branch line had been designed and installed with code-compliant slope-to-drain.
2. Stoppages were relatively infrequent, suggesting a cause other than a design or installation deficiency or a subsequent problem such as pipe crushing or settlement.
3. Low-flow toilets, which had just been made a requirement by the state environmental regulators, were beginning to get a lot of bad press for a number of functionality problems including the failure of downstream waste lines to clear after flushing.
4. A professional engineer had advised the architect to use a 4-inch line (3-inch would have been code-permitted) and to keep the slope to code minimum (1/8-inch per foot) to enhance the scouring effect of each flush.
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