Donald Hester
Washington State Licensed Home Inspector #647
WSDA#80050
InterNachi Member #NACHI10022401
509-670-9572
Contact Us
Washington State Licensed Home Inspector #647
WSDA#80050
InterNachi Member #NACHI10022401
509-670-9572
Contact Us
DonHester's blog
Crowning achievement, old plumbing venting styles- Crown Vents
Submitted by DonHester on Tue, 10/17/2017 - 09:04.
Crowning achievement, old plumbing venting styles- Crown Vents
Wenatchee Home Inspections
I love inspecting older homes. There is always fun to find the remnants of years past.
On a recent home inspection I found one of those relics, a “Crown Vent”. Crown venting, as its name implies, is a vent that is taken from the top of the trap called the crown. This method of venting once was once an allowed practice, provided it is properly installed and correctly connected with the use of proper fittings. But as we learned more about venting practices the “Crown Vent” was no longer allowed in modern plumbing by code.
A "Crown Vent" is a vent that is located within 2 pipe diameters of the trap it is serving. The issue is if the vent is that close it is more likely to be subjected to fouling of hair, soap oils, grease, and other debris. Because of the close proximity of vent the flow of water does not have a chance to dissipate thus reaching the top of the pipe where the vent is during discharge causing premature failure.
Crown Vent
Venting Theory has it roots in the 19 century when in 1874 the vent theory was proved. Without proper venting objectionable odors and sewer gases were escaping at fixture waste outlets. By providing a vent air pressures in the drainage piping system were kept the same and the trap seal was kept from being siphoned.
From the UPC-
901.0 General.
901.1 Vents Required. Each plumbing fixture trap, except as otherwise provided in this code, shall be protected against siphonage and backpressure, and air circulation shall be ensured throughout all parts of the drainage system by means of vent pipes installed in accordance with the requirements of this chapter and as otherwise required by this code.
901.2 Trap Seal Protection.
The vent system shall be designed to prevent a trap seal from being exposed to a pressure differential that exceeds 1 inch water column (0.24 kPa) on the outlet side of the trap.
1004.0 Traps.
1004.1 Prohibited.
No form of trap that depends for its seal upon the action of movable parts shall be used. No trap that has concealed interior partitions, except those of plastic, glass, or similar corrosion-resisting material, shall be used. "S" traps, bell traps, and crown-vented traps shall be prohibited. No fixture shall be double trapped. Drum and bottle traps shall be installed for special conditions. No trap shall be installed without a vent, except as otherwise provided in this code.
These traps were prohibited as far back as 1955 UPC, section 704 (earliest version of this article I could find) and most likely even farther back.
"A human being: an ingenious assembly of portable plumbing."
Christopher Morley
If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.
NCW Home Inspections, LLC is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…
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