The ultraviolet radiation in sunlight causes degradation of the plastic composition of PVC pipe over time and, although it produces discoloration, the main problem is reduction in the impact resistance of the pipe. Instead of flexing under an impact, it is more likely to crack. CPVC pipe also has the same issue.

    Although a small amount of titanium dioxide is added to the formulation of many plastic pipes to boost their UV-resistance, JM Eagle, a major plastic pipe manufacturer, is typical of most other companies in their recommendation for protecting PVC installed in an exterior location and exposed to sunlight:

“For permanent above-ground PVC pipe installations, it is recommended that the pipe be protected from sunlight exposure. This can be accomplished by wrapping the pipe with an opaque material or, more commonly, by painting it. If the pipe is to be painted, a water-based latex paint formulated for exterior use is recommended. Oil or solvent-based paints may damage the pipe and/or not adhere well. In order to minimize heat build-up, white or light-colored latex paints are best.”

    The drain pipe shown in the photo at the top of this page, that runs from a mobile home to the septic tank, has another defect besides the exposure to sunlight of the PVC. The area above ground has no required protection from damage. While the amount of soil coverage or other protection necessary will vary according to the dictates of the local building department, some sort of shielding from damage is also required. Since the degradation of PVC stops when it is no longer exposed to sunlight, if soil coverage over the exposed pipe is provided, painting the PVC is not necessary.

    Also see our blog post Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water?

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Here’s links to a collection of our other blog posts about PLUMBING PIPES:

• How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

• Can galvanized steel pipe still be used for new water lines in a house? 

• How can I tell if I have cast iron pipes in my house? 

• Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection? 

• What is the difference between green and white sewer drain pipes?

• Is a washing machine drain hose required to be secured at the standpipe?

• What are the abandoned pipes sticking out of the wall in my house?  

• What are the code requirements for plumbing vent terminations?

• What are the code requirements for layout of drain piping under sinks?

• What causes a gurgling sound when a bathtub or sink drains? 

• If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?  

• How can I tell what type of plumbing pipe I have?

• Why is there a flexible accordion pipe under the sink? 

• What is the difference between PVC and ABS plumbing pipe?

• What is the difference between water service pipe and water supply pipe? 

• What are the pipes on my roof? 

• How can I find out what type of water pipe runs underground from the water meter to the house (service pipe)?

• What is a P-trap?

• Why is old galvanized steel water pipe a problem for homebuyers?

• What does polybutylene pipe look like? Why is it a problem? 

• Which water pipes are an insurance problem and possibly uninsurable?

• Can you connect CPVC pipe directly to a gas water heater?  

     Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.