Over time, the trim around your windows shows its age. Wood casings crack, sills rot, and paint peels no matter how often you scrape and recoat. Replacing exterior window trim is one of the most effective ways to improve curb appeal and protect the wall around each window, and replacing it with composite mouldings means you won't be doing the job again in a few years.
The short version: Remove the failed trim, repair any water damage behind it, then install a composite surround and sill that will not rot. Browse exterior window trim and matching window sills.
Signs It's Time to Replace Your Window Trim
- Soft spots when you press the trim with a screwdriver, especially at the bottom corners and the sill.
- Paint that peels or blisters again within a year or two of repainting.
- Open joints, cracks or gaps between the trim and the wall.
- Staining on the wall below the window, a sign water is running where it shouldn't.
- Trim that simply looks dated or out of proportion with the house.
Why Replace with Composite Instead of Wood
Wood is the traditional choice, but windows are where it fails first: rain and condensation collect at the joints and sill, and painted wood traps that moisture. Mouldex composite mouldings have a lightweight, moisture-inert foam core with a hard cementitious coating, so they:
- will not rot, split or attract insects;
- hold their shape through seasonal temperature swings, with near-zero joint expansion;
- have a smooth, stone-like finish that takes paint well;
- come in modern and traditional profiles, or can be matched to your existing trim.
Compare every option in our exterior moulding materials guide.
Step-by-Step: Replacing Exterior Window Trim
- Choose your profile. Pick a casing that suits the house: slim, squared surrounds such as the Kamloops for modern homes, or bold stepped profiles such as the Eaton for traditional facades. Add a matching sill for a complete surround.
- Measure each window. Measure the width and height of each opening and note the wall type (stucco, brick, siding, stone). Send us your measurements for a quantity takeoff.
- Remove the old trim. Carefully pry off the old casing and sill without damaging the window frame.
- Inspect and repair. Check the framing and sheathing behind the old trim. Replace any rotted wood and make sure flashing and the weather barrier are intact and lapped correctly so water drains outward.
- Install the sill first. Set the sill with a slight slope away from the window so it sheds water, then adhere it per the installation guidelines. For the sill details that matter most, see why window sills fail.
- Install the casing. Cut the side and head pieces to length, mitre or butt the corners as the profile requires, and adhere them to the wall with exterior adhesive, adding fasteners where specified.
- Seal the joints. Caulk where the trim meets the window frame and the wall, leaving drainage paths open at the bottom.
- Prime and paint. All Mouldex mouldings are primed and painted after installation.
Tips for a Professional Result
- Keep the same profile and proportions on every window of an elevation.
- Scale the trim to the wall: larger windows and taller walls need wider casings.
- Coordinate window trim with door trim so the whole facade reads as one design.
Frequently Asked Questions
Can I install new window trim over the old trim?
It's better to remove the old trim. That lets you inspect for hidden rot and water damage and gives the new trim a flat, sound surface.
Do composite window trims need painting?
Yes. They are primed and painted after installation, then need no rot repairs or re-sealing of the trim itself.
Can you match my existing window trim?
Yes. Send photos, drawings or a sample and we can make a custom profile to match, which is ideal when replacing only some windows.
Ready to replace your window trim? Browse exterior window trim, order a free sample kit or send us your window measurements.
