Details, Schmetails

By Timothy Allinson, P.E.

Murray Company, Long Beach, Calif.

I would like to start by wishing everyone a very happy and healthy New Year. By the time this article reaches your desk I will have a new son, my second, and last, child. I think his name will be Nolan, although his brother wants to name him Luke (after Luke Skywalker). This may be one of the few times Aidan does not get his way. My wife Mila - Aidan's wonderful mother - will surely have the final say on the baby's name. As of this writing, there are still other names in play, and we will wait until we see his face to decide for sure. So, on to other details ...

I am presently involved in an interesting project, the renovation of a historical theater here in Los Angeles, the Mark Taper Forum. Ironically, my father, who is an actor, performed on this stage several times when I was a very young boy. I surveyed the theater, and one of the things I learned during the survey was that the play currently running was Nightingale, a one-woman show starring Lynn Redgrave. By chance, I saw that the last performance of the show was on November 19, the day that my father was arriving for his Thanksgiving visit. Considering the fact that Ms. Redgrave is a personal friend of my father's, and considering that they have performed together several times, I, of course, had to get tickets.

The night of the performance my father and I forgot one very important detail: We forgot to get him an assisted listening device. My dad wears hearing aids, but they are useless in the theater. By the time we realized our mistake, it was too late to correct it. So Dad, who couldn't hear a word of the play, sat there struggling to stay awake. We had planned on going backstage after the performance to congratulate Lynn, but, since Dad hadn't heard a word of the show, he was too embarrassed to follow through with that plan. So, instead, we left the theater to get a glass of wine.

While we sat at the bar in a nearby restaurant, I recounted the performance for my father so that he was able to feel that he had, essentially, seen the play: It was a great bonding session for the two of us. He offered me riveting details of his friendship and past experiences with Lynn and others in their circle. As this conversation came to a close, Ms. Redgrave and her director happened to walk into the restaurant for dinner. After my father confessed his embarrassing error, we were able to enjoy a very nice talk with Lynn that made the entire evening complete.

With that interesting but irrelevant information out of the way, I can dive into the subject at hand. At the first design coordination meeting of the Mark Taper renovation, I learned from the structural engineer that the second floor north, the location of the new dressing rooms - the most plumbing-intensive aspect of the project - was a very structurally sensitive area of the building. When I pointed out the problems associated with putting fixtures in new locations in this delicate area, the design team stared at me blankly as if it were my problem to fix.

"Can't you use the existing slab penetrations?" they asked.

"No," I responded.

After getting down to brass tacks, the biggest challenge seemed to be the dressing room lavatories located on the perimeter wall. The architect noted, "There are existing dressing room lavatories located along that same wall. How far can the waste from the new lavatory locations run in order to utilize the existing sleeves?"

Hmmm ... To my surprise, I realized that this was a question I had never pondered in detail in my 22-year career. "I'll have to check," was the only honest reply I could offer.

Back at the office, I spoke with Dick Drenske (a founding member of ASPE) about the governing criteria for this lavatory issue. The result of that dialogue is shown in Figure 1. The standard lavatory waste outlet is located 18" above the finished floor. The dimension from there to the bottom of the short sweep elbow is 9.75", as shown. In order to keep the no-hub coupling above the slab, the minimum dimension from the horizontal waste to the floor is 5.25". So, 18" minus 9.75" and 5.25" leaves only 3" for pitch. Since the 2" waste is required by code to run at 1/4" per foot, the maximum distance that the waste can run is 12 feet. (Note that for 1/4" pitch the distance the pipe can run is the elevation change in inches times 4, yielding feet. For 1/8" pitch the distance is the elevation change in inches times 8.)

So, the answer to the architect's question was, "The waste from the new lavatory locations can run 12 feet." That's not very far - less than I would have guessed. True, it is possible to stretch another four feet of distance from the run if you bury the no-hub coupling in the floor, but this requires potentially messy fireproofing and waterproofing details and is best avoided. Alternatively, the drain outlet from the fixture can be raised an inch or so to gain a few more feet, but this also gets a little messy, since it requires trimming the drain tailpiece.

It is not often that the plumbing designer needs to examine this level of detail in his or her designs. However, since it drove the design solution, this was a necessary level of detail to calculate. It is important to know when this amount of detail is necessary and when it is not. Calculating it unnecessarily does not do the profitability of a project any good. However, neglecting such details when they are critical can cause a project costly redesign by the installing contractor.

At the design-build mechanical contracting firm where I work, I am continually amazed by the level of detail practiced by the team that produces our shop drawings. This team is appropriately called the Detailers, and, as I have written before, they are the ones who transpose the conceptual design shown on the construction documents into a buildable reality. I wish it were mandatory for every plumbing designer to spend at least a week working shoulder to shoulder with a seasoned detailer, as it would surely be a great learning experience. Personally, I never stop learning from this team.

I have learned that it is essential to get the detailers involved early, at the beginning of every new design-build project. When designing a 400-unit high-rise condominium, for example, even the smallest design error can have significant effects on project cost when it is repeated 400, 800, or 1,200 times.

Another design detail that I would like to touch on before closing is that of wall space requirements and architectural coordination. Recently, I was asked how much space is required in the wall at the foot of a bath/shower. Most would answer that the space should be the dimension of the shower valve, which traditionally fits in a 3-5/8" stud. The correct answer, however, depends on several issues. In some cases, the answer given would be correct. But if the bath/shower were in a typical location in a high-rise building, the water risers would likely run vertically in that same wall. The hot water riser could easily be as large as 2" where it begins its vertical run. Depending on the code governing the project, that pipe might require as much as 1.5" of insulation, making it 5" in size and requiring at least a 6" sleeve. In many specs this sleeve might be required to protrude an inch or more above the floor, meaning that it cannot conflict with the sheetrock wall. Allowing for construction tolerances, the outside dimension of that wall would be at least 8". This is a fundamental issue that the vast majority of architects do not understand, and one that we grapple with at the beginning of all of the projects we design. It is unfortunate that these space issues are not covered sufficiently when today's young architects are receiving their education.

Timothy Allinson is a Senior Professional Engineer with Murray Company, Mechanical Contractors, in Long Beach, Calif. Prior to entering the design-build industry he worked for Popov Engineers, Inc. in Irvine, Calif, and JB&B in New York City. Tim holds a BSME from Tufts University and an MBA from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a leed Accredited Professional. Tim is a past-president of ASPE, both the New York and Orange County Chapters, and sits on the board of the Society of American Military Engineers, Orange County Post.