CPVC Design Considerations for High-Rise Buildings
Editor's Note: Table 2 couldn't be reproduced online. Please see the print issue for this figure.
Although chlorinated polyvinyl chloride (CPVC) pipe and fittings have more than a 40-year proven service history, their use in high-rise applications has increased significantly only in recent years, as more and more plumbers and engineers have become aware of both their installation and performance benefits.
CPVC is an ideal material for high-rise use because of its cost-effectiveness and ease of installation. From a long-term maintenance and reliability standpoint, CPVC pipe is also ideally suited for high-rise use because it will never corrode, pit or scale. In addition, CPVC pipe is available in copper tube size (CTS) from 1/2" to 2" and in iron pipe size (IPS) from 2-1/2" to 16" in diameter.
CPVC pipe is also certified by NSF International and meets ANSI standards for use with potable water. It can be used with all water pH levels. Additionally, CPVC pipe and fittings meet all applicable ASTM standards and building codes. Copper-tube-size CPVC is manufactured with an SDR 11 (Standard Dimension Ratio) wall thickness. SDR 11 means that there is a constant ratio of 11 between the wall thickness and outside diameter of the pipe. This constant ratio results in a pressure rating of 100 psi at 180
A Faster, More Efficient Bonding SystemA key advantage to installing a CPVC system, from a labor and a safety perspective, is that an easy solvent cement bonding system eliminates the need for an open torch on the jobsite. The solvent cement bonding system utilized with CPVC piping products is fast, safe and requires few tools. CTS systems up to 2" in diameter can be pressure-tested in as little as 15 minutes after a simple five-step installation process.
Step 4: Apply solvent cement-When making a joint, apply a heavy, even coat of cement to the pipe end. Use the same applicator without additional cement to apply a thin coat inside the fitting socket. Use only CPVC cement or an all-purpose cement conforming to ASTM F-493, or joint failure may result.
Solvent cements that do not require the use of a primer have been developed for CTS systems. These "one-step solvent cements" are yellow in color and are in compliance with the current versions of the Uniform Plumbing Code and International Plumbing Code. Solvent cements that require the use of a primer are orange in color. These "two-step solvent cements" can be used with CTS pipe and fittings and are required for use with IPS pipe and fittings.
Pressure-testing procedures should be performed in accordance with local code requirements in the same manner as would be followed with metallic pipe. When pressure testing, the system should be filled with water and all air bled from the highest and farthest points in the run. If a leak is found, the joint must be cut out and discarded. A new section can be installed using couplings. During sub-freezing temperatures, water should be blown out of the lines after testing to eliminate potential damage from freezing. When hydrostatic testing is not practical, refer to the pipe and fittings manufacturer's recommendations.
Transitions, Piping Supports and SpacingThere are a wide variety of transition fittings (male and female) available for easy transitioning between CPVC pipe and metal. Care should be used, however, so as to not over-torque CPVC threaded fittings, and additional support should be added at the metal side of the transition to support the added weight of the metal system. TFE (Teflon®) thread tape is safe and recommended for making CPVC threaded connections. Some paste-type sealants, however, may contain solvents that could damage CPVC. Should you choose to use a paste or pipe dope, double check that it is compatible with CPVC.
Horizontal piping hanger/support spacing varies based on water temperature and pipe diameter. In general terms, however, CPVC piping should not be anchored tightly to supports, but rather secured with smooth straps or hangers that allow for movement caused by expansion and contraction. Full circle talon straps are usually recommended because they do not pin the pipe tightly against joists or other structures. Hangers should not have rough or sharp edges that could possibly come into contact with the pipe.
Vertical runs (risers) of CPVC pipe should be supported by pipe clamps or by hangers located on the horizontal connection close to the riser. Hangers and straps that do not distort, cut or abrade the piping should be utilized. To maintain vertical piping in straight alignment, use supports at each level plus a mid-story guide.
CPVC pipe can pass through wood studs and joists without the need for insulators between the CPVC pipe and a wood structure. To permit movement caused by expansion and contraction, holes drilled in the wood joists and studs should be 1/4" larger than the outside diameter of the pipe. Wood or plastic wedges that restrain the pipe as it passes through the wood joist or stud should not be used.
When CPVC pipe passes through metal studs, some form of protection must be used to protect the pipe from abrasion and to prevent noise. Plastic insulators, rubber grommets, pipe insulation or similar devices may be used for this purpose.
Thermal Expansion and ContractionLike all piping material, CPVC expands when heated and contracts when cooled. Regardless of diameter, CPVC piping will expand about 1 inch per 50 feet of length when subjected to a 50-degree temperature increase. Therefore, allowances must be made for this resulting movement. The stresses developed in CPVC pipe are generally much smaller than those developed in metal pipe for equal temperature changes because of the difference in elastic modulus. Required loops are typically smaller than those recommended for copper systems.
Expansion is mainly a concern in hot water lines. Generally, thermal expansion can be accommodated with changes in direction; however, a long, straight run may require an offset or loop. Only one expansion loop, properly sized, is required in any single straight run, regardless of its total length. If more convenient, two or more smaller expansion loops, properly sized, can be utilized in a single run to accommodate thermal movement.
Hydraulic Design ConsiderationsHydraulic calculations for sizing of CPVC pipe and fittings should be calculated using a Hazen-William C Factor of 150. And since CPVC will never pit or scale, the C Factor remains constant over time.
A maximum design velocity of 10 feet per second is typically utilized for both hot and cold water CTS CPVC systems. A design velocity of 5 feet per second is typically used for larger diameter IPS CPVC systems. This design velocity is based on both field experience and laboratory investigation. See Tables 1-4 for friction losses at different flow rates for both Schedule 80 and SDR 11 piping.
Penetrating Fire-Rated Walls, Combustibility and Flame/Smoke SpreadBuilding codes require penetration through fire-rated walls, floor and ceilings to be protected with approved penetration firestop systems. A number of firestop manufacturers have systems specifically listed for use with CPVC pipe. Consult the UL Fire Resistive Directory, Warnock Hersey Certification Listing, or the PPFA Plastic Pipe in Fire Resistive Construction Manual for a listing of products.
There are many misperceptions regarding the combustibility of CPVC, which has a flash ignition temperature of 900