Replace a Glass Block Window With One That Opens
Glass block lets light in and nothing else: no air, no view, no way out. We take it out of the foundation and put in a basement window that slides or tilts open.
JMB Builders will replace a glass block window with a window that opens, anywhere in the Twin Cities metro. We cut the mortared block out of the foundation opening, clean the masonry, anchor a treated or PVC-wrapped buck, set the vinyl slider or hopper you bought in a sill pan, foam and seal it inside and out, and trim it. Priced per window, labor only or with the window supplied, quoted from photos within one business day.
- Priced per window, labor only or window supplied
- Block cut out, buck framed, window sealed and trimmed
- Quote from photos in 1 business day
- Licensed MN contractor BC809005
Glass block went into a lot of Twin Cities basement windows in the 1980s and 1990s because it does not rot, does not get broken into, and does not need painting. It also does not open. The first summer you want to air out the basement, or the first time you finish a room down there, the block becomes the problem. The fix is to cut it out and set a real window in the opening.
The block is mortared into the foundation, so removal is masonry work: score the joints, break out the block, chip the mortar bed flat and clean the opening. Then the opening needs a wood buck anchored to the concrete so the window has something to fasten to, a sill pan so water that gets past the window runs out and not in, and a window sized to the buck. Most block openings take a standard vinyl basement slider or hopper.
JMB Builders does glass block window replacement across the Twin Cities metro. Buy the window yourself and we install it labor only, or we supply it. Either way we cut out the block, build the buck, set the window, seal it inside and out, and trim it so the inside matches the rest of the basement.
What you supply
- A photo of the block window from inside and outside, with a tape measure across the width and height of the masonry opening
- The window, if you are buying it: a vinyl slider or hopper sized to the opening after we confirm the buck dimensions, or ask us to supply it
- Whether the basement is finished, being finished, or staying bare, which sets the interior trim
- Paint or stain for the interior trim — painting is quoted as a separate line, or leave it primed and caulked and paint it yourself
What JMB supplies
- Removal of the mortared glass block and haul-away of the debris
- Cleaning and flattening the masonry opening
- Treated or PVC-wrapped buck anchored to the concrete, sized to the window
- Sill pan, flashing tape, low-expansion foam, backer rod and exterior sealant
- The window itself when you want us to supply it, quoted as its own line
- Exterior trim or sealant detail to the foundation, and interior jambs and casing or a drywall return
- Painting or staining of the interior trim when you want it done, quoted as its own line
- Photos of the finished window in your job folder
How it is priced: per window
Quoted in writing from your photos within one business day. What moves the number:
- Size of the block opening and how much block there is to cut out
- Poured concrete vs. block foundation, which changes how the buck is anchored and how the opening cleans up
- Whether the window you bought fits the opening as is or the buck has to be built out to a smaller window
- Window well or grade at the outside: a window at grade needs the exterior sealed and sloped more carefully
- Interior finish: bare buck in an unfinished basement vs. jambs and casing or a drywall return in a finished one
- Labor only on your window vs. us supplying the window
- Number of block windows swapped in the same visit
A tape measure across the masonry opening in the photo, inside and out, lets us tell you what size window to buy and quote it firm.
How long it takes
One glass block window out and a new window in, sealed and trimmed: about half a day. Two or three in a day. Interior trim in a finished basement may be a second short visit.
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
Vinyl basement slider
The most common replacement: a horizontal slider with a screen, sized to the buck. Easy to open from inside, ventilates well, and the big-box stores stock standard sizes that fit most block openings with a little buck adjustment.
Hopper window
A single sash hinged at the bottom that tilts in. Fits the short, wide openings glass block usually sits in, seals tight when latched, and is the traditional basement window. Good where a slider would be too small to be worth opening.
Block opening in a window well
Block windows below grade sit in a steel or plastic well. We keep the well, clean out the debris, and seal the new window to the foundation with the well in place. If the well is rusted through or full of dirt, we tell you before we start.
Not an egress window
A slider or hopper in a block opening lets air in; it does not make a bedroom. An egress window for a bedroom needs a much larger opening cut in the foundation, a deeper well and a drain, which is a different job. If that is the goal, tell us and we point you the right way.
Replace a Glass Block Window With One That Opens: questions, answered
Can a glass block window be replaced with a window that opens?
Yes. The block is cut out of the foundation opening, the masonry is cleaned flat, a wood buck is anchored to the concrete, and a vinyl slider or hopper is set in a sill pan, foamed, sealed and trimmed. Most block openings take a standard basement window size with a small adjustment to the buck. JMB Builders does this across the Twin Cities metro, labor only on a window you bought or with the window supplied.
How do you remove a mortared glass block window?
Carefully and with a lot of dust control. We score the mortar joints, break out the block a course at a time, and chip the mortar bed off the sill and jambs so the opening is flat and clean. The blocks and mortar are hauled away. If the block was set in a metal channel or had an old wood frame behind it, that comes out too. The opening is then measured for the buck and the window.
What window should I buy to replace a glass block window?
A vinyl basement slider or a hopper in the size closest to your masonry opening, allowing for a wood buck on all four sides. Measure the width and height of the masonry opening, inside and out, and send the photos; we tell you the exact window size to buy before you order. Big-box stores stock standard basement sizes, or we can supply the window and add it to the quote.
Will a new basement window in a block opening be an egress window?
No. A glass block opening is small, and a slider or hopper in that opening gives you light and air, not an emergency exit. An egress window for a bedroom needs a much larger opening cut through the foundation, a bigger well and a drain, which is an excavation job, not a window swap. If you want a bedroom in the basement, say so up front and we help you sort out what that takes.
Is a glass block window more secure than a vinyl window?
Glass block is hard to break through, which is why it went in. A vinyl slider or hopper with a good latch is secure enough for most homes, and you can add a locking bar or a window well cover. The tradeoff is real: block gives you security and no ventilation; a window that opens gives you air, egress from a fire in a finished room, and a latch. Most homeowners who finish a basement make the swap.
Do you supply the window or do I?
Either. Buy the window yourself and we install it labor only, after confirming the size against your opening so it fits the first time. Or ask us to supply it and we add the window as its own line on the quote. Labor is the same either way: block out, buck in, window set in a sill pan, foamed, sealed and trimmed.
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
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