question about sanitary lines in nonresidential buildings



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    Joel Edwards

    I feel like the keyword in this question is "nonresidential". The benefits of cast iron (muffles sound of water moving through pipes, durability, noncombustible) make it a much better option for commercial applications. Building tenants do not want to hear water rushing through a conference room wall when a toilet flushes and commercial building owners want to minimize the number of plumbing maintenance calls. Since cast iron is noncombustible, it can be installed in return air plenums that commercial buildings sometimes use as part of their HVAC system.

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    Michael Ermann

    Jumping off of Joel's excellent response, below is an excerpt from my book on the subject of piping noise for those interested in geeking out. . . 

    Plumbing Noise Checklist

    Early Design

    1. Locate supply and drain lines away from quiet areas such as walls common to bathrooms and


    2. Locate bathrooms, laundry rooms, and kitchens to minimize the need for horizontal drain


    3. Use a simple plumbing layout to avoid fittings and bends, and allow for large radius turns in

    piping to minimize water turbulence noise.

    4. Avoid designing plumbing fixtures on sensitive walls, such as party walls, or walls shared with

    a bedroom.

    5. Back‐to‐back bathrooms should have completely separate framing, such as a double wall, so

    that one unit’s piping does not contact a neighbor’s unit. Similarly, double walls should be

    used wherever a chase wall joins a bedroom.

    Isolation from the Structure

    1. Use oversized pipe supports such as clamps, straps, and hangers. Wrap pipes in a collar of

    resilient material (rubber, neoprene, mineral wool, or fiberglass) at the band where the pipe

    would otherwise make contact with the support.

    2. Attach pipes resiliently to the most massive structural elements, such as masonry walls.

    3. Where pipes penetrate a wall or floor‐ceiling assembly, use an oversized sleeve and wrap the

    pipe at the penetration point with a band of resilient material. Seal the penetration well—on

    both sides of the penetration—with water‐resistant non‐hardening caulk to avoid airborne

    noise transmission.

    4. If resilient underlayments are not used in the floor, isolate bathtubs, showers, washers, dryers,

    and toilets on a pad of cork, neoprene, rubber, or other resilient material to mitigate sounds

    from falling water, rotating equipment, and slamming toilet seats.

    System Design

    1. Use cast‐iron waste pipes rather than PVC waste pipes. They are much quieter. For supply

    lines, plastic is often quieter than metal. This is what Joel pointed out, above.

    2. Recognize that some fixtures, such as pressure‐assist toilets, are inherently noisier than other

    types of fixtures.

    3. Take care with high‐pressure plumbing systems, including those associated with chilled water

    distribution, because they are inherently noisy. Maintain the static pressure of main water

    supply lines of buildings with three stories or less at less than 50 psi. Branch lines serving

    individual apartment units should not exceed 35 psi. In high‐rise structures where high‐pressure

    main supply lines are required, pressure reducers or regulators should be used in supply

    branches to meet these limits.

    4. Properly size piping so that plumbing systems are not under high pressure and velocity. Flow

    velocities less than 6 feet per second (2 meters per second) in domestic systems are found to

    be less likely to elicit complaints.

    5. Design flexible connectors to attach the plumbing system to vibrating equipment such as

    pumps, washers, dishwashers, garbage disposals, air‐handling units, and chillers.

    6. Box large‐diameter supply and drain pipes, in gypsum board enclosures, particularly in highpressure

    systems. Install fiberglass insulation on the inside of the enclosure.

    7. Design waste pipes and pipes associated with roof drains to run in walls adjacent to rooms

    that are less noise sensitive, such as utility rooms or kitchens. Avoid running pipes (especially

    PVC waste pipes) in walls adjacent to bedrooms, living rooms, or dining rooms.

    Kara, What do I mean when I write about isolating the pipes from the structure (by far the most important thing besides not running pipes through quiet spaces)? See the drawing below.

    For a more broad overview. . .

    Plumbing Noise

    Although plumbing noise often isn’t especially loud, it can be disproportionately annoying to

    occupants. This is because (1) it arrives in an on‐off cycle, and intermittent noises are judged to

    be more annoying than continuous ones, (2) when it arrives at night, even if it isn’t very loud, it

    may be loud enough to interrupt rest, and (3) when associated with bathroom activities it can be

    embarrassing and feel like an invasion of privacy. Plumbing noise complaints are most common

    in multifamily dwellings.

    Amplification A vibrating cell phone may be almost inaudible if left on the living room couch, but when left

    on the dining room table it’s easily heard throughout the home. In the same way, pipes and

    fixtures are, by themselves, poor radiators of noise. Rather, it is when a noisy or vibrating

    plumbing system is coupled to efficient noise radiators such as walls, ceilings, and floors

    that these sounds are amplified. For this reason decoupling the plumbing system from the

    structure is the best way to mitigate most plumbing noise.

    Turbulent flow and


    High water pressure and the resulting high water velocities cause turbulence and cavitation

    (noise from the collapse of water bubbles). This is particularly troublesome at bends, valves,

    taps, and connectors and is associated with the hissing sound sometimes found around

    partially opened fixtures.

    Water hammer Sudden interruption of water flow, as when one abruptly turns off a tap, forms a shock

    wave. This can also occur if one abruptly turns on a tap.

    Defective parts Loose or worn fittings and valves can cause chattering. These are easy to pinpoint by

    listening, and the noise often occurs when a tap is partially opened but disappears as it is

    opened further.

    Expansion and


    Often, but not always, associated with hydronic heating, the expansion and contraction

    of pipes can cause snapping and creaking, especially when pipes are rigidly connected

    to structure. Hot water radiators should be mechanically attached with flexible tolerances.

    Long hot water pipe lengths demand expansion joints.

    Draining water Draining of a fixture annoys with a gurgling sound. This is especially acute when drainpipes

    move vertically, then horizontally, as water falling hits the horizontal portion of the pipe.

    When the horizontal pipe is rigidly attached to a ceiling, it can excite the structure,

    amplifying the noise of the draining water.


    The book is available free to you through NCARB's Continuum Education (from your MyNCARB page I think). Look for the seven part "Architectural Acoustics Illustrated" course. It's just a pdf of the book in seven parts.


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    Kara Zhang

    Joel Edwards Thank you for your reply. Will the waste erose the cast iron pipe?

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    Joel Edwards (Edited )

    Kara Zhang All materials will degrade over time but the life expectancy of properly specified cast iron pipe will be similar to the life of the building itself.

    Speaking from personal experience, I lived in a 60 year old house and the cast iron pipes had just started to degrade to the point where occasional leaks occurred. The house's foundation was slab on grade and the cast iron was exposed directly to the soil under the foundation. I would expect cast iron pipe protected within a building to last much longer than that.

    I am thoroughly enjoying the questions you are asking! I am also studying to take the PPD test for the first time later this month and our discussions are helping me feel much more confident about taking the exam. Keep up the good work and I know you will pass your exam soon enough!

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    Kara Zhang

    Michael Ermann Joel Edwards


    Thank you for your reply. I really appreciate it.

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