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New Standard Specifies Syphonic Roof-Drainage Systems

How should rain water be syphoned from the roof of a stadium-sized warehouse? ASTM Standard F 2021, Specification for Design and Installation of Plastic Syphonic Roof Drainage Systems covers syphonic drainage of large industrial or commercial structures with a single roof. With a higher flow capacity, syphonic drainage has advantages over conventional systems. It uses fewer roof drains or outlets, and eliminates numerous downspouts that carry rainwater to the ground level storm sewer, according to Paul Sample, Ph.D., a plastics and piping consultant who is president of Samples, Inc., Wilmington, Del.

Approved in June by ASTM Committee F17 on Plastic Piping Systems, Standard F 2021 will address key issues, says Sample, the acting vice-chairman of ASTM Subcommittee F17.63 on DWV (drain, waste and vent). “This standard provides performance criteria necessary to accomplish functional roof draining with safety and cost considered,” explains Sample, who led the task group that developed the specification. “It establishes a protocol for employing a well known principle (vacuum) to a potentially troublesome construction feature, that of roof drainage. This standard will set the pattern of expected performance for any manufacturer or installer of roof drain system.”

In a March 2000 article in PE Engineer magazine, Arthur Scott, Ph.D., a professor in the Department of Building Engineering and Surveying, Heriot-Watt University, Scotland, notes a few installation and design concerns of syphonic drainage: “Siphonic roof drainage represents a significant advance in technology when compared to conventional systems,” he writes. “Siphonic roof drainage can result in savings in both cost and time during the construction phase. However, ...there are still uncertainties regarding just how these systems operate—particularly during priming. This lack of understanding of system operation means that if a system fails, it is often difficult to appreciate why the failure has occurred. Furthermore, as siphonic system design necessitates a higher level of expertise than is required for conventional systems, the performance of these systems can be more reactive to small inaccuracies and erroneous assumptions. To resolve this, over the past five years there has been an increasing amount of independent research underway attempting to understand how siphonic systems actually perform.”

This includes the research of ASTM’s task group of construction-product manufacturers, DWV consultants, resin suppliers, and those experienced in DWV product installation and performance who describe requirements of necessary syphonic drainage components and system performance criteria in ASTM F 2021.

“This standard was developed to describe a previously unaddressed means (syphoning) for efficiently removing rain water from nominally flat-roofed buildings,” concludes Sample. “Syphoning is a well known principle used for the natural movement of fluids through a tube or pipe by employing negative pressure or vacuum. This standard presents the necessary design requirements for functional performance of such a system and cites the limitations. Properly designed and installed, a syphonic drainage system will operate more efficiently, be self-cleaning and require less piping than gravity drainage systems.”

Technical questions may be directed to Paul Sample, Ph.D., Samples, Inc., 308 Walden Rd., Wilmington, DE 19803-2424 (302/656-3212). Committee F17 meets Nov. 13-16 in Orlando, Fla. For meeting or membership information, contact manager Pat Picariello, ASTM (610/832-9720). //

Copyright 2000, ASTM