Corner Window Replacement — Two Units, the Corner Post and the Header
Two windows meet at the corner of the room with only a thin post between them, and the corner is leaking, drafty or sagging.
Reply within one business day. Or call / text 763-204-2099.
Corner window replacement means taking out the two windows that meet at a house corner and the post or mull between them, checking that the header and corner framing still carry the load, and setting two new units joined at a new corner post, flashed as one opening. JMB Builders does it across the Twin Cities metro and north to St. Cloud. Priced per window; photo reply within one business day, or book a free in-home estimate.
- Priced per window, corner post listed
- Header and corner checked before ordering
- Flashed as one opening around the corner
A corner window has no corner wall. The roof or floor above the corner is carried by headers that meet over the glass and by whatever is in the corner: a post, a steel angle, or sometimes only the old window frames. That is why corner windows sag, why the glass cracks and why the corner joint leaks. Pulling the old units out without knowing what holds the corner is how a corner drops.
At the measure we look at the header line, the corner post and the sill for sag and rot. Where the corner is carried by a proper post and headers, the new units go back the same way. Where the old frames were doing the work, temporary support goes in during the swap and a header or post that size is sized by an engineer before anything is ordered.
The new windows are ordered as two units with a corner post or a factory corner joint, depending on the brand. The sill pan wraps the corner, the corner joint is flashed and sealed top to bottom, and the outside corner gets trim or capping to match. Interior trim at the corner is quoted on the same job.
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 763-204-2099.
What you supply
- Your choice of window style for each side: fixed, casement or awning
- Frame color and glass to match the rest of the house
- Furniture moved back from the corner on install day
What JMB supplies
- Measure of both openings and a check of the header, post and sill
- Two new units with a corner post or corner joint, per the brand
- Temporary support during removal where the corner needs it
- Sill pan wrapped around the corner, flashing and sealant
- Exterior trim or capping at the corner
- Interior corner trim quoted as part of the job
- Haul-away and photos of the finished corner in your job folder
How it is priced: per window
Quoted in writing from your photos, with a reply within one business day. What moves the number:
- Size and style of each of the two units
- Corner post, mull or factory corner joint
- Header or post work found at the measure
- Rot in the sill or corner framing
- Exterior cladding: siding, stucco or brick
- Second-story corner and access
Send a photo of the corner from inside and outside, plus a close-up of any sag, crack or water stain at the top of the corner.
How long it takes
Most corner window replacements take one to two days once the units arrive. Framing repairs or an engineered header add time, which is written on the quote.
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.
Corner Window Replacement — Two Units, the Corner Post and the Header: questions, answered
Can a corner window be replaced without replacing the whole wall?
Yes. The two units and the corner post come out, the framing is checked, and the new units go back in the same openings. Siding or drywall is opened only as far as the flashing and trim need. If the header or corner framing is failing, that repair is listed on the quote before work starts.
Why is my corner window leaking at the corner?
The vertical joint where the two windows meet is the hardest spot to flash, and it is often only caulked on the outside. Once the caulk cracks, water runs down the joint into the sill and the wall below. On replacement, the joint is flashed and sealed top to bottom and the sill pan wraps the corner.
Is a corner window structural?
The roof or floor above a corner window is carried by headers and a corner post or angle, not by a wall. In some houses the old window frames ended up carrying load as the framing settled. We check it at the measure, use temporary support during the swap, and a header or post that size is sized by an engineer when it needs changing.
Can I get a glass-to-glass corner window with no post?
Some brands make a corner unit with a slim joint instead of a full post, and the corner has to be carried by the framing above, not the glass. Whether it works depends on the brand line and on what holds your corner. We check both at the measure and tell you what is possible.
Is a corner window replacement priced as one window or two?
As two windows plus the corner post or corner joint, each on its own line. Any header, post or rot repair at the corner is a separate line, so you can see where the cost comes from.
Can you replace just one side of a corner window?
It can be done, but the new frame meets the old one at the corner, so the joint, color and sightlines often do not match, and an old failing side keeps leaking into the new one. Most corner windows are replaced as a pair.
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 9, 2026 · JMB Builders LLC, MN license BC809005 · All windows pages
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