Replace exterior wood trim: more wood or PVC?
May 10, 2016 4:07 AM   Subscribe

The wood in contact with my front steps has rotten away. Fixing it will be a DIY job. Should I replace the wood with more wood, or change to PVC? I'll be adding flashing behind the new trim, but otherwise the same wet conditions would remain.

I guess I'm pretty agnostic about which way to go. I've never worked with PVC, other than pipes.

Whatever I use will be painted, and I'm aware paint on PVC can take longer to dry. Installation would be limited to below-the-knee, which limits the PVC "look," though I obviously don't want this to end up looking cheap.

Have you worked with PVC trim? Any thoughts?
posted by Admiral Haddock to Home & Garden (8 answers total)
I don't especially like cutting PVC trim, but once cut, it's not bad to work with. We replaced the threshold in my sweetie's garage service-door with a PVC one a year ago, since the concrete under it collects any melt-water from snow that comes in on her boots. It's holding up very well, and I'm glad we bought the (pre-colored) PVC rather than trying to put in a piece of green-treated lumber.

I've never tried to paint it, because we got the trim in a pre-colored brown that matched her other trim pretty darned well.
posted by DaveP at 4:15 AM on May 10, 2016

Is this the door trim or the sill trim at the base of the house? I'm not clear on where it is but generally, any wood in direct contact with concrete should be pressure treated.

If it's vertical trim coming down and touching the concrete, there should be a 1/4 inch gap (with flashing behind) so the wood doesn't touch.

PVC trim works just fine as long as it's designed for exterior applications. Anything that's used for vinyl siding also works. With the plastic type trims be sure and follow manufacturer instructions to allow for the different expansion that temperature changes cause.
posted by mightshould at 4:22 AM on May 10, 2016

Thanks for the answers so far. It's the plinth blocks (and maybe parts of the pilasters) and the riser below the threshold, which I'll probably replace as well.
posted by Admiral Haddock at 5:10 AM on May 10, 2016

We used PVC trim under our eaves - it's a nightmare to paint (well) because the paint doesn't absorb into the PVC, so it's very easy to have drips/uneven coats/etc etc. however, once completed you never have to think of it again.
posted by Suffocating Kitty at 5:16 AM on May 10, 2016

Is this something you can use cement board, a la Hardie Board, for? The previous owners of our house covered the addition in that and it still looks *new* eight years on.
posted by notsnot at 5:55 AM on May 10, 2016 [1 favorite]

I have had good service from my cement board trim, even in damp areas. It also hold paint very well.
posted by Midnight Skulker at 8:11 AM on May 10, 2016

Hoo, boy. PVC trim, eh? I have some thoughts about that, yes I do.

As an employee of a remodeling company that does a ton of exterior trim replacement, I can tell you that PVC is very popular with homeowners right now. As in, probably 90% of the trim that we sell is PVC rather than wood. Homeowners love the idea of trim that requires no maintenance and never has to be replaced, and they're absolutely willing to pay extra for it. At least, that's how it is in my region (New England). Everybody who can afford it is getting PVC trim right now, almost without exception.

Again as an employee but speaking off the record now, I'm pretty ambivalent about it. "No maintenance, never replace" is a classic salesman's lie. PVC develops algae problems. It gets permanent stains if organic matter (leaves, dirt) is allowed to rest on it for any length of time. It's very easily damaged by rocks, weed-whackers, and all the other abuse that exterior trim has to put up with—moreso than wood, because it's much softer. If you paint it it will eventually need to be repainted just like anything else, and like anything else you can only repaint it so many times before it starts to look crappy. It doesn't rot though, so it certainly has that going for it.

As a carpenter I'm kinda meh about it. It's not that it's that much harder to work with than wood, it's just less interesting. It has some annoying aspects; it's much floppier than wood, and it'll melt if you cut it wrong, and it's harder to hide any minor mistakes that you make with it. Unhidable mistakes also cost more, because the material costs more. It makes a mess when you cut it, and the "plastic snow" doesn't just fade into the dirt and grass the way sawdust does, so you have to be a lot more thorough about dust collection and cleanup. You often have to take special precautions with your seams and joints (such as gluing them) in order to avoid having them open up when it gets cold, as PVC has a very high thermal expansion coefficient. Also I'm sure the little bits that you inevitably inhale while cutting it can't be good for you.

As an environmentalist, I implore you not to use it. Pine is a renewable, sustainable, biodegradable, carbon-neutral resource! PVC is none of those things. It's a non-renewable resource that will turn into eternal garbage as soon as its useful life is over. PVC trim is not made from recycled plastic, and it is unlikely to be recycled when it is removed from your house. Its production is much more toxic than wood, and the shift in construction from wood to plastic-based products contributes greatly to our society's ever-increasing use of non-renewable fossil carbon. I don't have any control over my company's decision to use the stuff so freely—and it's in such demand that we'd probably miss out on a lot of business if we refused to use it—but I die a little inside every time I see a pallet of snow-white plastic boards show up on a jobsite. Please, if you care at all about preserving the Earth for future generations, choose wood. Unlike so many other occasions in life, this choice is entirely yours to make. Please don't choose plastic.
posted by Anticipation Of A New Lover's Arrival, The at 6:31 PM on May 10, 2016 [3 favorites]

Oh, and a side note: if you do end up going with wood trim, you can greatly reduce the "rotting from the bottom" effect if you prevent it from directly contacting whatever is underneath it—concrete or dirt or brick or whatever the substrate around your front steps is. Surface substrates are almost always porous materials, and wood (especially end grain) will wick up any moisture that's present in those substrates, given the opportunity. You can stop this by putting a barrier in between the bottom of the trim and whatever it is resting on—either a piece of non-porous adhesive flashing or a bead of 100% silicone—or, better, by letting the trim stop just above the ground, so that there is a small air gap. Either strategy will ensure that water cannot wick up into the wood and cause it to rot away at the bottom. Builders don't usually bother to do this, but it makes a big difference over time.
posted by Anticipation Of A New Lover's Arrival, The at 6:41 PM on May 10, 2016 [2 favorites]

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