Bonus Room Over the Garage Window Replacement — The Cold Room Fixed
The room over the garage is ten degrees colder than the rest of the house, the windows frost inside, and the kids will not sleep up there in January.
Reply within one business day. Or call / text 763-204-2099.
Bonus room over the garage window replacement covers a truss room above an unheated garage, with windows in the gable end or a shed dormer on the garage roof. JMB Builders replaces those windows across the Twin Cities metro, foamed and flashed into the roof wall, with the insulation gaps around the frame fixed while the wall is open. Priced per window, quoted from photos or at a free in-home estimate, with a reply within one business day.
- Priced per window, gable and dormer units
- Frame gaps foamed and sealed while the wall is open
- Dormer units flashed into the garage roof
The bonus room over the garage, the FROG in a builder's plan, is framed in attic trusses above a garage that is not heated. Cold comes at it from five sides: the garage below, the roof slopes on two sides, and the gable or dormer walls where the windows are. The windows in those walls are the thinnest part of an already cold room, and in many of these houses they went in fast, with a gap at the frame stuffed with a little fiberglass and no air seal.
When the windows are replaced, that gap is the thing worth fixing. The old unit comes out, the rough opening is cleaned to the framing, and the space between the new frame and the studs is foamed with low-expansion foam and sealed inside and out. On a dormer window the exterior wall sits on the garage roof, so the flashing has to tie into the step flashing and the roof, not just the house wrap. That is where the leaks and the ice at the window head start.
The glass matters too. The bonus room gets the full sun through a gable window in summer and loses heat through it all winter, so the glass package is picked for the exposure. If the room is a bedroom, the windows are kept at the egress size the code calls for. Painting is quoted as a separate line — or leave it primed and caulked and paint it yourself.
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 pick of style, exterior color and glass; casement or double hung to match the house
- Whether the room is a bedroom now or will be, so egress size is checked
- Photos of each window from inside, from the driveway, and a close-up of the frame where it meets the roof
- A look at the knee-wall access if there is one, so we can see the insulation behind the window wall
What JMB supplies
- In-home measure of each opening and a look at the insulation around the old frames
- The windows, ordered to size
- Old units out and hauled away, floor covered
- Rough opening cleaned, foamed with low-expansion foam and sealed inside and out
- Sill pan and flashing tied into the dormer or gable wall and, at a dormer, into the roof step flashing
- Interior stool, apron and casing matched to the room, or jamb extensions on a drywall return
- Exterior capping or trim to finish the outside
- Photos of the finished windows 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:
- Gable-end windows reached from the driveway vs. dormer windows on the garage roof
- Insert in a sound frame vs. full-frame with the opening foamed and re-flashed
- Dormer flashing tied into the roof and step flashing
- Rot at the sill from ice at the window head or a leaking dormer
- Glass package picked for a sun-facing gable
- Two windows vs. a gable unit and two dormers in one visit
Send one photo from the driveway showing the whole garage wall and roof, one of each window inside, and a close-up of the outside corner where the window frame meets the siding or roof.
How long it takes
A bonus room with two or three windows: one day, including the foam and flashing work at each opening. Dormer windows on a steep garage roof may add a half day for roof access.
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
Gable-end window over the garage door
The big window centered over the garage. Often a fixed unit with a casement each side, or a double hung pair. Reached from the driveway with ladders or a lift; the sill and the header are checked for rot from years of frost.
Shed dormer windows on the garage roof
Two or three small windows in a dormer wall that sits on the garage roof. The flashing is tied into the roof step flashing and the dormer siding, which is where the old ones leaked.
Bonus room used as a bedroom
At least one window kept at the egress size the code calls for, with the sill height checked. A casement gives the largest clear opening in a small dormer.
Windows plus knee-wall insulation
While the windows are open, the insulation and air sealing in the knee walls and around the window wall are fixed from the attic side. Quoted as its own line when the knee-wall space is accessible.
Bonus Room Over the Garage Window Replacement — The Cold Room Fixed: questions, answered
Why is the room over my garage so cold even with the heat on?
It is surrounded by cold: the unheated garage below, roof slopes on two sides, and gable or dormer walls full of windows. The windows and the gaps around their frames are the weakest point. In many of these rooms the frames were set with a fiberglass stuffing and no air seal, so cold air pours in around the window even when the glass is new. Foaming and sealing the frames when the windows are replaced is a big part of the fix.
Will new windows alone warm up a bonus room over the garage?
They help a lot, and fixing the air leak around them helps more, but the room also loses heat through the garage ceiling and the knee walls. If the windows frost inside and the drafts are at the frames, start with the windows and the foam around them. If the floor is cold, the garage ceiling insulation is the next thing. We look at both at the estimate.
Why do the dormer windows over my garage leak?
The dormer wall sits on the garage roof, and the window in it has to be flashed to the wall and the wall flashed to the roof. If either was skipped, water that runs down the roof gets behind the window. Ice at the window head in winter does the same from above. On a replacement, the window is flashed to the wall and the wall flashing is tied to the step flashing on the roof.
Does a bonus room over the garage need egress windows?
If it is used as a bedroom, yes: at least one window has to give the clear opening the code calls for. If it is a playroom or an office, no. Because these rooms often become bedrooms later, we recommend keeping at least one window at the egress size when you replace them, and we check the existing clear opening before ordering.
Can you insulate around the bonus room windows while they are out?
Yes. With the old unit out, the rough opening is open to the studs and the gap is filled with low-expansion foam, then sealed inside and out. If the knee-wall attic space behind the window wall is accessible, the insulation and air sealing there can be fixed at the same time as a separate line on the quote.
How do you reach windows in a dormer on the garage roof?
From the garage roof itself, with roof brackets and planks on a steep pitch, or from a lift in the driveway. The slope and the height decide which. Both are set up and taken down the same day, and the roofing under the brackets is left as it was.
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 10, 2026 · JMB Builders LLC, MN license BC809005 · All windows pages
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