phc April 2022 www.phcppros.com

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SPECIAL TO PHC NEWS

significant market share in single- family residential construction. It is interesting to note that many plumbing professionals commonly refer to solid wall PVC pipe as "Schedule 40" and cellular core pipe as "foam core," conflating the topics. For an engineer reviewing submittals, it is important to remember that both solid wall and foam core are manufactured to Schedule 40 dimensions. Schedule 40 refers only to the dimensions of the pipe (O.D., wall thickness, etc.) and has nothing to do with the material composition of the pipe. If engineers scan the piping submittals and see "Sch 40," they may think they are getting solid wall PVC pipe. Submittals for solid wall PVC pipe will contain references to ASTM D2665 and ASTM D1785.

Code compliance

The ASTM F891 manufacturing standard is referenced in all major model plumbing codes. As with any code item, always check with the authority having jurisdiction for acceptability, limitations or restrictions. In some local jurisdictions, cellular core pipe is not permitted in commercial construction. It is important to remember that code compliance is the minimum requirement for performance of any given material. Just because a product meets the code does not mean that the material is optimal, or even viable, for a particular project. So, how does cellular core PVC pipe compare with solid wall PVC pipe? Engineers, designers, specifiers, contractors, building owners and facility managers should evaluate the performance capabilities of all materials based on the requirements of the specific project over the life of the structure. Here are several points to consider: Strength: In buried applications, a commonly asked question is "What is the crush strength of PVC pipe?" The questioner often wants a simple answer in tabular format and is sometimes frustrated with the complexity of the answer. As flexible systems, both cellular core and solid wall PVC piping systems work with the surrounding soil to support an earth or live load, termed the "soil-pipe mechanism." For that reason, the crush strength of a section of PVC pipe in a press without the support provided by the surrounding soil is not relevant. The Iowa Formula is commonly used for this purpose. The Uni-Bell PVC Pipe Association publishes a very helpful calculator based on the Iowa Formula that is available as a free download from its website (uni- bell.org). Uni-Bell's Handbook of PVC Pipe Design and Construction is an excellent and inexpensive reference that aids in the use of the calculator. The Uni-Bell calculator allows a designer to input variables specific to the application, including maximum allowable deflection, soil modulus, load parameters, additional live loads, pipe diameter and pipe stiffness. Pipe stiffness values for these equations can be taken from the applicable ASTM standards and are available from pipe manufacturers. The table on this page lists the pipe stiffness values from the ASTM F891 and ASTM D2665 standards. The pipe stiffness values differ for foam-core PVC and solid-wall PVC pipe for smaller diameters, eventually merge at 8-inch diameters, but diverge again at diameters of 10 inches and 12 inches. When these values are entered into the Iowa Formula, the results demonstrate a greater load capability for solid wall PVC pipe than form core. Sound attenuation: Many consider foam core PVC pipe to be the "loudest" DWV pipe. Sound attenuation is a function of material density. The more dense the piping material, the better sound attenuation it provides. The chart on the next page shows the perceived "loudness" provided by the three most common types of DWV piping systems. While advocates of foam core PVC pipe contend that the market offers numerous products that can be used for sound abatement on these systems, many times the addition of sound-attenuation materials can negate the cost savings that foam core PVC pipe offers. Keeping in mind that a contractor's biggest cost factor is labor, does it make financial sense to go back a second time and install more material on the same system? For facilities and structures that require minimal ambient noise levels, such as schools, hospitals, upper-end residential and condominiums, foam core pipe will probably not be the optimal material choice. Temperature capabilities: Cellular core PVC pipe is manufactured from the same PVC compound as solid wall PVC pipe. It, therefore, has the same temperature capabilities as solid wall PVC. Both PVC products have a maximum operating temperature of 140 degrees. Installation: Both cellular core and solid wall PVC pipe are joined using