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Homeowners look for a trim contractor when paint keeps peeling on the same boards, when a screwdriver sinks into a soft sill or corner board, when new siding or windows mean the trim has to be redone, or when an older house needs mouldings rebuilt to match the originals. The work ranges from replacing one rotten section to wrapping all the trim in aluminum or remaking heritage details by hand.
This page covers trim materials, where rot starts, the pros and cons of aluminum capping over wood, painting and caulking, lead paint on old trim and heritage details. For work on the roof edge itself, see our soffit and fascia page.
Types of exterior trim: casings, corner boards, frieze, fascia and sills
- Window and door casings: the boards framing each opening, usually topped by a head casing with a drip cap or flashing to shed water.
- Sills: the sloped piece under a window that throws water away from the wall, and the trim most exposed to rain and snow.
- Corner boards: vertical boards at outside and inside corners that give the siding a clean edge to butt against.
- Frieze board: a horizontal band at the top of the wall, just below the soffit, that finishes the joint between siding and eaves.
- Fascia: the board along the roof edge that closes off the rafter ends and carries the gutters.
- Skirt boards, water tables and decorative mouldings: bands near the foundation, plus brackets, cornices and window hoods that define older styles.
Exterior trim materials: wood, PVC, composite and aluminum capping
The right material depends on how exposed the trim is, the style of the house and how much upkeep you're prepared for. Mixing materials is common, for example rot-resistant trim close to the ground and wood where detailed profiles matter.
- Wood: easy to mill into any profile and to repair in sections, and the authentic choice on older homes, but it needs primer and paint on every face and rots where water lingers.
- PVC (cellular vinyl): won't rot and can be milled and painted, but it moves more than wood as temperatures swing, so joints and fastening need care.
- Composite and engineered trim: wood fibres or other materials bound with resins, generally more stable than solid wood, with cut edges sealed as the manufacturer directs.
- Aluminum capping: prefinished sheet aluminum bent on site to wrap existing trim so it never needs painting, with trade-offs covered below.
Where water gets into exterior trim and causes rot
Trim rot starts where water sits or soaks in, and it often hides under paint that still looks fine. A screwdriver that sinks easily into ground-floor trim is the classic test; check higher trim with binoculars and leave closer inspection to the contractor. The usual trouble spots:
Soft trim can be a symptom of water reaching the wall, not just the board. When trim comes off, the contractor should check the sheathing, framing and window or door flashing behind it before closing up.
- Window sills and the bottoms of casings, where water runs down and pools on flat or back-sloped surfaces.
- Board ends that sit on or near a deck, step or the ground, where end grain wicks up moisture.
- Joints and mitres that open as wood moves, and failed caulking between trim and siding.
- Head casings with no drip cap or flashing, which let water run behind the trim and into the wall.
- Back faces and cut ends that were never primed, which absorb water from behind.
Aluminum capping over wood trim: pros and cons
Capping, or trim wrapping, covers existing wood trim with prefinished aluminum bent to fit each board. It's popular because it ends repainting, and over sound wood that stays dry it can protect the trim well. If you choose it, have rotten wood replaced first, and ask how the installer will lap the metal at sills, head casings and joints so water drains out rather than in.
- Pro: no more scraping and painting, with a factory finish in many colours.
- Pro: it can go over sound trim, keeping the original wood in place underneath.
- Con: if water gets behind the metal, the wood underneath stays wet and rots out of sight.
- Con: it hides the wood, so decay that was already there, or starts later, can go unnoticed until it's advanced.
- Con: bent metal flattens mouldings and fine profiles, changing the character of older homes, and dents are hard to fix invisibly.
Painting and caulking exterior trim to keep water out
On wood trim, paint is the weatherproofing. Once it peels or cracks, water gets into the grain, so trim often needs repainting before the siding around it, especially sills and the sunniest or most exposed sides. New wood trim should be primed on all faces and cut ends before it goes up, not only on the side that shows. See our exterior painting page for preparation and paint choices.
Caulking seals the joints between trim and siding and around windows and doors, but it doesn't replace flashing, and it shouldn't close the gaps and weep openings that let water drain out. See our exterior caulking page for sealant types and how old caulk is removed.
Repairing or replacing rotten exterior trim
Localized rot can often be cut out and replaced with a new piece of the same profile, joined with angled splices that shed water. Small damaged areas on detailed mouldings can be rebuilt with epoxy consolidants and fillers made for exterior use, which keeps original material in place.
Full replacement makes sense when rot runs through most of a board, when you're changing materials, or when new siding or windows mean the trim has to come off anyway. In that case, plan the trim, flashing and siding together so the details work as one system.
Lead paint and heritage approvals for old exterior trim
Old trim usually carries many coats of paint. Health Canada says lead-based paint is probable in homes built before 1960 and that homes built from 1960 to 1990 may have it on exterior surfaces. It advises against sanders, heat guns and torches, which release toxic dust and fumes, and suggests lab testing of paint chips or a contractor with lead-detection equipment. Ask how the crew will test, contain debris and clean up before any scraping.
Trim carries much of a heritage house's character. In Quebec, repairing or changing the appearance of a classified building, or one in a declared or classified heritage site or protection area, requires authorization from the Ministry of Culture, and municipalities set the rules for cited properties; capping trim or changing a moulding profile can alter that appearance. The Standards and Guidelines for the Conservation of Historic Places in Canada favour repairing original elements and replicating those that can't be saved, which on trim usually means milling new pieces to match.
Exterior Trim: frequently asked questions
Is aluminum capping a good idea over wood trim?
It can be, over sound wood with careful detailing at sills and joints so water drains out. Over rotten wood or with poor detailing, it hides decay and can trap moisture. On heritage homes it also flattens the mouldings that give the house its character.
What's the difference between fascia and a frieze board?
Fascia runs along the roof edge and carries the gutters; the frieze board sits on the wall just below the soffit and finishes the top of the siding. See our soffit and fascia page for work at the roof edge.
Can rotten trim be repaired instead of replaced?
Often, yes. Small rotten sections can be cut out and replaced with matching pieces, and exterior epoxy repairs can save detailed mouldings. When rot runs through most of a board, replacing it is the better fix.
Why does paint keep peeling on my window trim?
Usually because moisture is getting into the wood from behind or through unsealed ends, open joints or failed caulking. Repainting alone won't last; find and fix the water source, then prime and paint properly.
Could my old trim have lead paint?
According to Health Canada, it's probable in homes built before 1960 and possible on the exterior of homes built from 1960 to 1990. Have chips tested before any sanding or scraping, and hire a contractor who works lead-safe.
Sources
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides