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What are the Alternatives?

We soaked five types of trim in a bucket of water for about a month. That’s not a scientific simulation of real-world conditions, and most of these products aren’t intended for that kind of punishment. Still, we think the results are worth sharing:

Cellular PVC and poly ash:

These two materials were completely unaffected — which is just what you would expect from products rated for ground contact.

Fiber cement:

This seemed unaffected by the water, which surprised us because, unlike the cellular PVC and poly ash, it is not approved for ground contact.

Composite and engineered wood:

Both of these trim types swelled near the edges but did not blister or blow apart.

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Cellular PVC

Because it is made from plastic, cellular PVC trim will probably last longer than the rest of the house. It is rot-and-insect-proof and does not absorb water, which makes it a great option for trim that will get wet a lot. It is also the most expensive — about twice as much as other manufactured options.

Cellular PVC looks and cuts just like wood and comes in traditional widths and thicknesses. You can work it with regular power tools, blades and router bits. When temperatures rise or the sun hits it directly, cellular PVC does expand quite a bit along its length, so it is important to fasten it well with nails or screws. Be sure to drive screws all the way through the sheathing and into the framing members. You’ll need to leave 1/8 of an inch of space for heat expansion per 18 feet of trim (skip this if it is already hot outside).

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Composite

Composite trim looks just like medium-density fiberboard (MDF), but is made to handle weather extremes. It is basically wood fibers mixed with resins with chemicals added for insect and rot resistance. You can cut and rout it just like wood, it comes primes, and it holds paint very well. Here’s a roundup of naturally rot-resistant woods.