By EA Paint & Light Carpentry7 min read
At a glance
- Use PVC on
- Sills, water tables, corner-board bottoms
- Use wood on
- Detailed, historic or matching trim
- Dark colors
- Check the trim maker’s rules first
- New wood trim
- Prime all six sides first
Is PVC trim better than wood trim?
For trim that stays wet, such as sills, water tables, the bottoms of corner boards and anything near the ground, a roof or a deck, cellular PVC is usually better because it cannot rot. Wood is still better for detailed and historic profiles, matching existing trim, and easy painting. Many houses are best served by both.
What PVC trim actually is
Exterior PVC trim, often called cellular PVC, is a foamed plastic board made to the same nominal sizes as wood trim. It cuts, routes and nails with ordinary carpentry tools, it is usually white all the way through, and it is sold as boards, sheets and ready-made mouldings.
Its big advantage is simple: it does not absorb water, so it cannot rot, swell or feed mildew the way wood does. Its tradeoffs are different from wood’s, not absent, and knowing them is what makes the difference between a PVC repair that lasts and one with gaps at every joint.
PVC is not the only alternative to ordinary pine. Fiber cement and engineered composite trim boards are also sold for exterior use, and naturally rot-resistant woods such as cedar hold up better than common pine when they are kept painted. Each has its own installation rules. This guide compares wood and PVC because they are the two most homeowners are choosing between when a piece of trim has rotted.
PVC trim vs wood trim: side by side
The two materials fail in different ways, which is why the right answer depends on where the board goes.
Rot and moisture
- Wood trim
- Rots if it stays wet; needs paint and sealed joints
- Cellular PVC trim
- Does not rot or absorb water
Movement
- Wood trim
- Swells and shrinks with moisture
- Cellular PVC trim
- Expands and contracts with temperature
Painting
- Wood trim
- Must be painted or stained to last
- Cellular PVC trim
- Can be left white; paints well with the right product
Dark colors
- Wood trim
- No special limits
- Cellular PVC trim
- Heat can cause movement or distortion; check the manufacturer
Detailed profiles
- Wood trim
- Easy to mill and match old mouldings
- Cellular PVC trim
- Stock profiles are limited; custom milling possible
Fastening
- Wood trim
- Standard exterior fasteners
- Cellular PVC trim
- Specified fasteners and spacing; holes filled
Look up close
- Wood trim
- Wood grain, crisp painted edges
- Cellular PVC trim
- Smooth or embossed; reads slightly different
Expansion, contraction and joints
Wood moves with moisture. PVC moves with temperature, along its length, and a long run of PVC trim on a sunny wall grows and shrinks noticeably between a hot summer afternoon and a winter night. Installed carelessly, that shows up as joints that open in winter or boards that bow in summer.
Manufacturers publish installation instructions that cover this: how close the fasteners go, which fasteners to use, how joints are made, and when joints are glued with PVC cement. Those instructions are the standard to hold an installer to, and it is reasonable to ask whether they will be followed.
Massachusetts makes this more noticeable than milder climates. Trim installed on a cold day is already contracted, and trim installed in summer heat is already expanded, so the season of installation affects how the joints behave later. Short pieces, such as a single sill or the bottom of a corner board, move very little; long horizontal runs, such as fascia, rake boards and water tables, are where the joint details matter most.
Painting PVC trim, including dark colors
PVC does not need paint to survive, but many homeowners paint it to match the rest of the trim or because white PVC picks up dirt. Clean, dry PVC generally takes a quality 100% acrylic exterior paint well, and because the board does not move with moisture, the paint tends to last longer than it would on wood.
Color is the caution. Dark colors absorb far more heat in the sun, and PVC softens and moves more as it heats. Many manufacturers limit how dark a color can be used, or require paints formulated for vinyl and other heat-sensitive surfaces, and painting outside those rules can affect the warranty. If you want dark trim, check the trim manufacturer’s painting instructions and choose the paint to match them.
Preparation is simpler than on wood but not skippable. New PVC can carry a film from manufacturing and handling, so it is cleaned before painting, and older PVC that has weathered or picked up dirt is washed first. Nail holes are filled with a filler made for PVC, and joints are finished according to the manufacturer before the paint goes on.
Tip: If you are unsure which brand of PVC is on the house, a painter can still use a vinyl-safe color range as the conservative choice.
Where each one belongs on a Massachusetts house
New England weather is hard on wood trim: rain, snow that sits against the house for weeks, ice dams and repeated freeze-thaw cycles all drive water into end grain. The pieces that stay wettest fail first, and those are the best places for PVC:
- Window and door sills and the bottoms of door brick mold
- The water table and skirt boards along the foundation
- The lower ends of corner boards and porch column bases
- Trim beside roof surfaces, decks and stair landings
- Any trim close to grade, where splash-back and snow keep it wet; no trim should be buried in soil or mulch
Where wood still wins
Wood is the better choice for detailed and decorative trim: crown and bed mouldings, built-up cornices, window heads with profiles, and anything that has to match existing work. A carpenter can mill or source a wood profile to match a 19th-century moulding far more easily than finding it in PVC.
Many Massachusetts towns have local historic districts with their own rules about exterior materials, and replacing visible wood trim with plastic may need approval. If your house is in one, check with the local historic commission before the work is planned.
When wood is used, the details decide how long it lasts: a durable species, primed on every face and cut end before installation, joints sealed, and clearance kept from roofs, decks and the ground.
Mixing materials on one house
On many houses the best answer is a hybrid. The bottom few inches of a corner board, the sills and the water table are replaced in PVC, while the window casings, frieze and decorative pieces stay wood. Once both are primed and painted the same color, the difference is hard to see from the ground.
A common sign that this approach makes sense is a house where the same few pieces have been repaired or replaced more than once. Those are the spots where the conditions, not the carpentry, are the problem.
It is still worth fixing the water where you can. A gutter that overflows onto a corner board, a sprinkler that hits the water table, or mulch piled against the trim will shorten the life of paint and caulk on any material, even if PVC itself will not rot.
What to ask before trim is replaced
Whether the job is a few sills or a full trim package, a good estimate should say:
- Which pieces are being replaced, and in what material
- How the new trim is fastened and how joints are made
- Whether new wood is primed on all sides before installation
- What paint will be used on PVC, and whether your color fits the manufacturer’s rules
- How rot found behind the trim will be handled and priced
Talk to a local crew
EA Paint & Light Carpentry is a painting and light carpentry company based in Northborough, MA. If you would like the house looked at, call (508) 466-5846 or request a free written estimate. Related services: Exterior Painting, Light Carpentry & Wood Repair.
