Not Widely Known
More and more synthetic materials are being used in the building trades. Vinyl siding, PVC pipes and their like have been around long enough that we know how they behave, but there are things about other products (cellular PVC trim boards, composite deck planks, etc.) that are not as widely known.
* Synthetic trim is not a direct replacement for wood. PVC (even cellular PVC) experiences far more thermal movement than wood and attachment provisions could differ from wood, depending upon a number of factors. Manufacturers could require extra fasteners and adhesives for certain configurations.
* Synthetic trim won’t rot, but it can degrade when exposed to the elements. Painting is recommended for some and required for others and there are considerations apart from adhesion and compatibility issues. Because of the elevated thermal expansion of plastics, certain colors are not recommended for exterior applications. Dark colors absorb more thermal energy from sunlight and the resulting rise in temperature will exacerbate movement problems. White is generally the best choice.
*Synthetic (composite) decking will not usually have the same strength as wood and its span rating is usually reduced. If you replace wood with composite, it may be necessary to add floor joists or other support.
These are just a few things to consider when dealing with synthetics. You should always consult with the material manufacturer before using, modifying or treating these products.