# Research about the new, lower, 5-foot head on DWV.



## Glenn (Feb 7, 2020)

Someone on the internet asked me about history on the 10-foot head of water for DWV tests.  How long has it been 10-feet is a question that comes to minds when people see it was lowered in the 2015 IRC.  Here is a video that takes the water test back to the 1800's and then shows how code changes can be researched, by researching this one.  Enjoy!


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## Sifu (Feb 10, 2020)

Just to add to your head test data.....the NC plumbing code only requires 3' above the highest fitting for 1/2 family dwellings.


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## jj1289 (Feb 10, 2020)

Glenn,

I have been doing research and going back to at least the 1957 South Florida Building only required a 5 ft head.

Sifu; do you have documentation on the reasoning for the 3 ft head test in NC?


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## Glenn (Feb 10, 2020)

jj1289 said:


> Glenn,
> 
> I have been doing research and going back to at least the 1957 South Florida Building only required a 5 ft head.
> 
> Sifu; do you have documentation on the reasoning for the 3 ft head test in NC?


I'm guessing Florida was on some version of the Southern Plumbing Code?  I don't have any old ones of those, but the 1997 edition (my oldest) is 10 ft.  I wonder if there's more story in the SBCCI code.  I need some old southern codes!  ha, ha!

If people use what I teach in the last half of this video, they will find the 2021 IRC will return to 10 ft...


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## Sifu (Feb 10, 2020)

jj1289 said:


> Glenn,
> 
> I have been doing research and going back to at least the 1957 South Florida Building only required a 5 ft head.
> 
> Sifu; do you have documentation on the reasoning for the 3 ft head test in NC?



It has been a day since I was there, but my assumption is that they arrived at the same conclusion as the code change submitter.  As inspectors, we didn't like the shake pipe method.  Aside from the possibility of getting wet, often the water was at the top of the pipe, sometimes in the heat of the day, the pipe would overflow, wetting some of the pipe below.  How does one differentiate between pipes wet from the top of the standpipe vs. from a leak?When I was inspecting a plumbing rough, I would mark the water level in the pipe as soon as I walked in, then check it at the end, and check the joints in between.  I will say we also mused over the fact that the vent pipes above the ceiling never got tested, and I can also say, outside of my capacity as a code official, that I climbed in several attics trying to trace leaks, and more than once found faulty (or never cemented) vent pipe joints at the wrong end of a slope.  Its a toss-up, some joints don't get tested, but those that do might get a better observation.  The head pressure is less in a 3' section of pipe, but a faulty joint will probably leak anyway.


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## jj1289 (Feb 11, 2020)

It appears from my research the 10 ft head came from piping coming in 10 ft lengths.  A 10 ft head of water equals 4.33 psi so I am assuming that is were the 5 psi air test came from.  But comparing air to water is comparing apples to oranges.  You need less air to find a link compared to testing with water due to surface tension and viscosity.


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