Bay Window Replacement — Bay and Bow Units, Seat, Roof and Trim
The seat is cold, the roof over it leaks, the glass is fogged or the whole unit has dropped. We replace the bay or bow and finish it inside, outside and on top.
JMB Builders does bay window replacement across the Twin Cities metro, for both bay and bow units. We quote from photos, measure in person, order the new unit, remove the old bay with its seat and head board, check the support, set the new unit with cables or brackets, roof and insulate it, and trim the inside and outside. Priced per window; quote within one business day.
- Priced per window, windows supplied
- Seat, head board, roof and support included
- In-home measure before anything is ordered
- Licensed MN contractor BC809005
A bay or bow is several windows joined into one projecting unit, with a seat board, a head board, a small roof, and cables or brackets holding it up. Any of those parts can fail: fogged glass in one sash, a seat with no insulation under it, flashing at the little roof that lets water into the wall, or a unit that sagged because it was never supported right.
Replacing one means handling all of it. The new unit is hung on proper support, the roof is flashed into the wall and shingled or capped, the seat and head are insulated, and the inside is trimmed so the seat board meets the wall clean. Some owners use the job to switch to a flat picture window or a smaller box bay.
What you supply
- Your choice of brand, color, glass, number of units and projection angle
- Seat and head board finish: wood species or paint grade
- Furniture moved away from the window wall
- Your paint or stain color — Painting is quoted as a separate line — or leave it primed and caulked and paint it yourself.
What JMB supplies
- In-home measure before ordering
- The bay or bow unit, ordered as a complete assembly
- Removal and haul-away of the old unit, seat and roof
- Support cables or brackets, and framing repair where needed
- Insulation under the seat and above the head board
- Roof over the unit, flashed into the wall and shingled or capped
- Interior seat, head board, jambs and casing, plus exterior trim
- Photos of the finished unit in your job folder
How it is priced: per window
Quoted in writing from your photos within one business day. What moves the number:
- Bay (three units, angled) vs. bow (four or more, curved)
- Overall width and projection, brand and glass package
- Roof over the unit: shingled hip roof, copper or metal cap, or under an eave
- Rot in the wall framing, floor or header found when the old unit comes out
- Switching to a flat picture window, which means closing in the floor and wall
- Interior seat and head board in paint grade vs. stain grade wood
Send photos of the unit inside and out, the roof over it, and the underside of the seat from outside.
How long it takes
One bay or bow replacement with roof, support and trim: one to two days. Staining or painting the seat adds time if it is part of the job.
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
Bay for a new bay
The same footprint with new units, support and roof. The seat and head are insulated this time, and the interior is trimmed to match the room.
Bow window
Four or more narrower units in a gentle curve. More glass across the wall, and more joints to seal, so it takes a longer install than a bay of the same width.
Bay to flat picture window
The projecting unit comes out and a flat window goes into the wall. The floor and wall below are closed in and the siding is patched. A fix for a bay that was always cold or kept leaking.
Bay Window Replacement — Bay and Bow Units, Seat, Roof and Trim: questions, answered
Can a bay window be replaced with a regular window?
Yes. The bay comes out, the opening is framed for a flat window, and the floor and wall area under the old projection are closed in and sided. It is more work than a like-for-like swap but it ends the cold seat and roof leaks for good.
What is the difference between a bay and a bow window?
A bay is usually three windows: a large center unit and two angled side units. A bow is four or more equal units set in a shallow curve. Both project out from the wall and both need a roof, a seat and support.
Why is my bay window seat so cold?
Many bay seats were built with little or no insulation under the seat board, and the platform hangs out past the heated wall. Cold air gets in from below and around the support. On a replacement we insulate the seat and head and seal the platform before the trim goes on.
My bay window is sagging — do I need a new one?
Not always. If the units are in good shape, adding cables or knee braces can lift and hold it. If the unit is also fogged, rotted or leaking, replacing it with proper support is the lasting fix. Send photos and we will say which.
Why is water coming in above my bay window?
The small roof over a bay is a common leak spot. The flashing where the roof meets the wall is missing, lapped the wrong way or failed. On a replacement the roof is rebuilt and flashed into the wall; if the unit is fine, the roof can sometimes be reflashed by itself.
How long does it take to replace a bay window?
Most bay and bow replacements take one to two days, including the support, roof and interior trim. The opening is closed and weathertight at the end of the first day.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners and for the builders and dealers we sub for. Counts come straight from our job log; no customer names.
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.
Related jobs we do
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Read morePage reviewed September 26, 2026 · JMB Builders LLC, MN license BC809005 · All windows pages
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Based in Zimmerman, scheduling across the Twin Cities metro. Closest first: