https://www.usplastic.com/knowledgebase/article.aspx?contentkey=774
Based on these studies, Harvel Plastic, Inc. recommends that PVC and CPVC piping products (i.e. pipe, duct, & shapes) exposed to the direct effects of UV radiation be painted with a light colored acrylic or latex paint that is chemically compatible with the PVC/CPVC products. Compatibility information should be confirmed with the paint manufacturer. The use of oil based paints is not recommended.
And from another source:
Some PVC (PVC UVR) is UV resistant. The sunlight still damages the PVC pipe, but it is in a matrix of other chemicals that compete for the UV light (stealing it away from the would be damaged PVC). PVC UVR will degrade, but at a slower rate.
If you need light weight, PVC works but paint it even if you get the UVR grade for more cost. Many options available.
Based on these studies, Harvel Plastic, Inc. recommends that PVC and CPVC piping products (i.e. pipe, duct, & shapes) exposed to the direct effects of UV radiation be painted with a light colored acrylic or latex paint that is chemically compatible with the PVC/CPVC products. Compatibility information should be confirmed with the paint manufacturer. The use of oil based paints is not recommended.
And from another source:
Some PVC (PVC UVR) is UV resistant. The sunlight still damages the PVC pipe, but it is in a matrix of other chemicals that compete for the UV light (stealing it away from the would be damaged PVC). PVC UVR will degrade, but at a slower rate.
If you need light weight, PVC works but paint it even if you get the UVR grade for more cost. Many options available.