Replace a Row of Three Windows as One Mulled Unit
Three windows sit in a row across the living room wall with a strip of siding and trim between each.
Reply within one business day. Or call / text 763-250-3621.
To replace a row of three windows as one mulled unit, JMB Builders measures the three openings and the studs between them and orders one factory-joined unit that fills the row: a picture window with openers on each side, or three matching sashes. A three-window row is a normal job for us, priced per opening in the unit. Twin Cities metro. Send photos and we reply within one business day, or book a free in-home estimate.
- A three-window row is a normal job, priced per opening
- One factory-joined unit replaces three separate frames
- Picture in the middle, openers at the sides, or three alike
Older ramblers and split-levels often have three separate windows in a row across the living room or family room wall, each in its own frame with a few inches of wall and trim between. From inside you see three windows and two posts; from outside, three boxes. Replacing them with one mulled unit turns that into one wide window with two slim mullions.
Mulled means joined. The three windows are built as one unit at the factory, or joined on site with a mull kit, so the frames share a reinforced post between them instead of a stud bay with siding on it. The row is usually a picture window in the middle for the view with casements or double-hungs on each side for air, or three of the same sash. Mixed styles inside one unit is normal.
What happens to the studs between the old windows is the real question. If the posts between the three windows carry load, the header over the row has to be checked, and a header that long is sized by an engineer. If the posts are only infill, they come out and the one unit goes into the widened opening. We find out at the measure, and the rest of the house's windows are checked then too so the new unit matches them in color and grilles.
Get a written quote for this job
Three photos and a sentence is enough: a reply within one business day, or ask for a free in-home estimate. Or text the photos to 763-250-3621.
What you supply
- A photo of the row from inside, far enough back to see all three and the wall between them
- A photo of the row from outside, showing the siding and trim between the windows
- A photo of a window you are keeping, for the match
- The room cleared in front of the wall the morning of the install
- Paint or stain color for new trim: painting is quoted as a separate line, or leave it primed and caulked and paint it yourself
What JMB supplies
- A quote with each opening in the unit priced on its own line, plus the framing and trim work
- One in-person measure of the row and the wall between, and a match check against the windows you keep
- One mulled unit through our supplier, factory-joined or joined on site with a reinforced mull
- Removal of the three windows and the infill between them, or new framing and a header where needed
- Sill pan or flashing tape, shims, low-expansion foam and sealant around the whole unit
- Interior casing, stool and apron across the full width, and exterior capping or trim to the siding
- Cleanup, haul-away of the old units, a permit when the city requires one, and photos in your job folder
How it is priced: per opening
Quoted in writing from your photos, with a reply within one business day. What moves the number:
- The three windows' sizes and the width of the finished unit
- The mix in the unit: picture window with openers, or three casements or double-hungs
- Whether the posts between the old windows carry load and a new header is needed
- Brand, series, frame material, glass package and grilles
- Siding, stucco or brick between and around the old windows that has to be opened and patched
- Interior finish: new casing, stool and apron across the width, drywall patching where the posts came out
- Second-story rows that need a ladder set or a lift for a heavy unit
A wide shot from outside that shows the siding between the three windows tells us a lot about what is in that wall.
How long it takes
Lead time depends on the line and is written on the quote. A three-window row as one unit: one to two working days, longer if a new header goes in.
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 reply within one business day. Prefer a look in person? A free in-home estimate is always an option.
- 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
Picture window with two openers
A fixed unit in the middle for the view with a casement or double-hung on each side for air. The most common row, and the one with the thinnest look because the center has no sash.
Three matching sashes
Three casements or three double-hungs joined in one frame, all opening. More air, a more traditional look, and the mullions read as part of the grille pattern.
Three separate windows, kept separate
When the posts between carry load and a header is not in the budget, three new windows go back in the three openings on one order. They match each other and the mullion covers between them are trimmed to read as one.
Replace a Row of Three Windows as One Mulled Unit: questions, answered
Can three separate windows be replaced with one mulled unit?
Usually, yes. The three windows and the infill between them come out, and one factory-joined unit goes in the widened opening. If the posts between the old windows carry load, a header has to be checked and perhaps replaced before the unit goes in. JMB Builders finds that out at the measure and quotes both ways. Send photos and we reply within one business day, or book a free in-home estimate.
What is a mulled window unit?
Two or more windows joined into one frame, at the factory or on site with a mull kit, so they share a reinforced post between them instead of a stud bay with siding on it. From inside and out it reads as one wide window with slim vertical lines where the units meet.
Can a mulled unit have a picture window and two casements?
Yes. Mixed styles in one unit is normal. A fixed center with an opener on each side is the most common three-window row, and all three parts come from one line in one frame color, glass and grille pattern.
Does a row of three windows need a new header?
Only if the posts between the old windows were carrying load. Many were just infill between three rough openings under one header already. If they do carry load, a header long enough for the row is sized by an engineer and goes in with the unit, and the permit covers it. We check at the measure.
How is a mulled three-window unit priced?
Per opening, three lines for the three parts of the unit, plus the framing and trim work as their own lines. This site does not publish dollar figures. The factory mull and the wider trim add some cost over three separate windows; a new header adds more.
Will one wide unit match the other windows in the house?
We check at the measure. The frame color, grille pattern and brand of the windows you keep are noted, and the unit is ordered in the closest current line. The openers at the ends of the unit are usually the same style as the rest of the house, so the row ties in.
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 the builders we work with. Counts come straight from our job log; no customer names.
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Read morePage reviewed October 25, 2026 · JMB Builders LLC, MN license BC809005 · All windows pages
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