Exterior Window Trim After New Siding Replacement
The siding is done, the windows are sitting in a thin strip of J-channel, and the house still looks unfinished. We trim them out in boards that shed water and last.
JMB Builders installs exterior window trim after new siding across the Twin Cities metro. When the siding crew wraps the windows in J-channel or leaves the nail fin bare, we add PVC or LP trim boards with a drip cap at the head, sealed to the window frame and lapped so water runs out over the siding, not behind it. Priced per window, quoted from your photos within one business day.
- Priced per window, exterior side only
- PVC or primed LP SmartSide trim boards
- Drip cap and flashing tape at every head
- Quote from photos in 1 business day
- Licensed MN contractor BC809005
J-channel is a siding part, not a trim part. It gives vinyl siding something to end into around a window, and a lot of siding crews stop there because trim boards are carpentry and carpentry is not what they bid. The result is a window with a skinny plastic edge and no real casing, and on the head of the window it often means the only thing keeping water out is a bead of caulk.
Trimming windows after a siding job means going back into the siding. On vinyl, the J-channel gets pulled or moved out, the trim boards go on against the window, and a new channel runs around the boards so the siding still has a finished edge. On LP, fiber cement or steel lap siding, the boards butt to the siding with a proper caulk joint. Either way the head gets a metal drip cap tucked under the housewrap or the siding above it, so water that runs down the wall goes over the trim instead of into the top of the window.
We use cellular PVC or primed LP SmartSide trim depending on what is already on the corners and what you want to maintain. Painting is quoted as a separate line — or leave it primed and caulked and paint it yourself. PVC can be left white with no paint at all.
What you supply
- Photos of two or three windows straight on and one from the side so we can see how the siding meets them
- A photo of a corner board or door trim if you want the new window trim to match it
- Your choice of trim width and material — we will suggest one from the photos
- Paint color if you want the trim painted; PVC can stay white
What JMB supplies
- PVC or primed LP SmartSide trim boards in a width that matches the corners and doors
- Metal drip cap at every head, flashing tape where the nail fin was left exposed
- New J-channel or a channel receiver around the boards on vinyl siding
- Exterior sealant at the window frame and at the siding joint, stainless or coated fasteners
- Cutting the siding back cleanly where it was run too tight to the window
- Painting of the new trim when you want it done, quoted as its own line
- Photos of the finished windows in your job folder
How it is priced: per window
Quoted in writing from your photos within one business day. What moves the number:
- PVC vs. primed LP trim boards, and the width of the boards
- Whether the J-channel has to be pulled and re-run around the new boards, or the siding just needs cutting back
- First-floor windows off a stepladder vs. second-story windows off ladders or staging
- Whether the head of the window has a drip cap now or needs one added under the siding
- Condition of the nail fin and housewrap at the window — bare fin takes flashing tape before trim goes on
- Painting the new trim, quoted as a separate line
- How many windows in the same visit — the setup is the same for one window or twelve
Send one photo of a window from a few feet back and one close-up of the top edge where the siding meets the window, and the quote covers the flashing too.
How long it takes
A single-story house with a dozen windows: one to two days. Second-story windows on ladders add time. Painting is scheduled after the caulk cures.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized quote within one business day. We only come out to measure first when the job needs a tape measure — no pressure, no games.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Situations and options
Trim boards with vinyl siding
The J-channel comes off, flat PVC boards go on tight to the window with a drip cap at the head, and a new channel runs around the boards so the siding has a clean edge again. It reads as real casing from the street.
Trim boards with LP, fiber cement or steel lap siding
The siding gets cut back to a straight line, the boards go on against the window, and the joint between board and siding gets a backer and sealant. Primed LP SmartSide trim matches the siding material; PVC works too.
Head trim and drip cap only
Some siding jobs leave the sides passable and the head with nothing but caulk. We add a head board with a metal drip cap tucked behind the siding above it, which is the piece that keeps water out of the top of the window.
Windows with a bare nail fin
When the fin was never flashed we tape it first — sides over the sill, head over the sides — then trim over it. Trim on top of an unflashed fin looks finished and leaks anyway.
Exterior Window Trim After New Siding Replacement: questions, answered
Why did the siding crew leave my windows in J-channel with no trim?
Because J-channel is the standard way to end vinyl siding at a window, and trim boards are a separate carpentry item that was probably not in the siding bid. J-channel by itself is not wrong, but it is thin, it does nothing to shed water at the head, and it looks unfinished next to real corner boards. Adding trim boards afterward is a normal job; it just means going back into the siding around each window.
Can you add exterior window trim after the siding is already on?
Yes. On vinyl siding we pull or move the J-channel out, set the trim boards against the window with a drip cap at the head, and run a new channel around the boards. On lap siding like LP or fiber cement we cut the siding back to a straight line, set the boards, and seal the joint. It takes a little more time than trimming before the siding, but the finished window looks the same.
Should I use PVC or LP SmartSide for window trim?
Cellular PVC does not rot, does not need paint, and stays white on its own; it is the safest choice around windows that get splashed or sit low to the ground. Primed LP SmartSide is an engineered wood trim that matches LP siding and takes paint well, but it does need to stay painted and sealed at the cuts. We usually match whatever is on the corner boards so the house reads as one trim package.
Do you flash the new window trim or just caulk it?
Both, and in that order. The head of every window gets a metal drip cap that tucks up behind the siding or housewrap above it, so water running down the wall is thrown out over the trim. If the nail fin was left bare we tape it before the trim goes on. Caulk is the last layer, not the only one; a window that depends on caulk alone will leak when the caulk gives up.
Do you paint the new exterior window trim?
Yes, painting is quoted as a separate line on the same quote — or leave it primed and caulked and paint it yourself. PVC trim can also be left white with no paint at all. Primed LP trim should be painted the first season it is on the house, including the cut ends.
Can the window trim match the corner boards the siding company installed?
Usually, yes. Send a photo of a corner board or the trim around a door and we will match the width and the material as close as it comes. If the corners are a vinyl lineal, we can still run PVC boards at the windows in the same width so the eye reads them as a set.
Get a written quote for this job
Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.
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Read morePage reviewed September 24, 2026 · JMB Builders LLC, MN license BC809005 · All window trim pages
Where we work
Window trim near you
Based in Zimmerman, scheduling across the Twin Cities metro. Closest first: