How to stop cold air coming through basement windows

Start by sealing the air leaks around the sash and frame, because moving air is what you feel. Then add a second layer of still air on the inside: shrink film on windows that stay shut all winter, or a removable insert on any window someone may need to open. Only box in a window with foam board if nobody will ever need to climb out of it. New double-pane glass costs the most, so it comes last.

TL;DR

• Air-sealing comes first and costs the least. HomeGuide prices weatherstripping at $5 to $10 per window, installed.¹
• Shrink film kits sold for $18.99 and $26.68 on Amazon when we checked in September 2026.² Keep film off any egress window.
• A removable insert is a 2x2 frame with plastic on both faces. It traps a pocket of air and still lets the window work.³ On an egress window, anyone in the house has to be able to pull it out by hand.
• Well covers keep snow, rain and debris out of the well.⁴ Over an egress well, the 2021 IRC says the cover must open from inside without a key or a tool.⁵ Local adoption varies.
• Storm windows run $150 to $400 each installed, and double-pane replacements $400 to $2,000.¹ Save them for windows that are failing.

Which basement window fixes give the most for the money?

Air-sealing gives the most for the least. Weatherstripping runs $5 to $10 per window installed, and it stops the moving air you feel first.¹ Shrink film and removable inserts come next for winter. Storm windows and new double-pane units help most with bad glass, but they cost hundreds of dollars per window.

Here's how the options line up. The ranking is ours. We put the lowest price we found first. Where no source we checked gave a price, we placed the fix by the materials and labor it needs.

The two HomeGuide guides disagree on weatherstripping. The window replacement guide says $5 to $10 per window, installed.¹ The egress window guide says $10 to $50.⁴ We'd budget from the higher figure for a large egress window, since that guide is about those units. For small basement windows, the lower figure is the better fit.

Which basement windows have to stay operable?

Any window that serves as the basement's emergency exit has to open from inside without keys, tools or special knowledge.⁵ That's the egress window, the emergency escape and rescue opening in the 2021 International Residential Code, section R310. Every fix on that window has to leave it working. Local adoption and amendments vary.

Here's what the model code says about basements:

• Basements need at least one operable emergency escape and rescue opening. Each basement sleeping room needs its own.⁵
• A basement used only for mechanical equipment, with no more than 200 square feet of floor, is an exception.⁵
• Bars, grilles, covers, screens and similar devices over an egress window or its well must come off from inside without a key, a tool or more force than it takes to open the window.⁵
• When an existing basement is altered or repaired, a new egress window is only required for new sleeping rooms.⁵

Walk the basement before you buy anything. Mark which windows are egress windows now, and which room might become a bedroom later. On Green Building Advisor, an expert member put it plainly: egress windows "should remain operable, or be replaced with something else that will meet code requirements as an emergency exit door."⁶ If a rental unit is in your plans, our basement apartments page covers what that build involves.

How do I insulate my basement windows?

Work from the leaks inward. Seal the sash with weatherstripping first. Then seal the frame where it meets the foundation. Last, add a layer of still air inside the glass with film or an insert. That order matters, because a cover over a leaky frame just lets cold air find its way around the edges.

Seal the sash

Self-adhesive foam weatherstrip tape is cheap and easy to find. Packs sold for $5.99 to $17.99 on Amazon when we checked in September 2026.² Clean the frame, press the tape where the sash closes, then open and latch the window to make sure it still works. On an egress window, always run that last test.

Seal the frame to the wall

Look where the window frame meets the concrete or block. Caulk small cracks. Fill wider gaps with a low-expansion foam made for windows and doors, so it doesn't bow the frame. If the wood is soft or rotten, a seal won't hold for long. That window belongs in the replacement pile.

Add a layer of still air

Once the leaks are closed, trap air on the inside of the glass. It's the same idea that makes insulated glass work: double- and triple-pane windows hold air or argon between the panes.¹ A homemade insert does it with plastic. "The double layer of plastic creates a pocket of air inside which insulates the window."³

What can I put over my windows to keep the cold out?

Put shrink film on windows that stay shut all winter, and a removable insert on any window you may need to open. Rigid foam board works on windows you'll never use, but it blocks all light. Keep film, foam and foil off an egress window unless the cover lifts out by hand with no tools.

Shrink film kits

A shrink film kit is plastic film and tape that goes on the inside of the frame. The Duck MAX kit on Amazon covers up to 5 windows for $18.99, or up to 10 windows for $26.68.² It's a good match for small basement windows you won't open until spring.

We'd keep film off an egress window. It's taped over the frame, so anyone escaping would first have to tear through it. The code asks for an opening that works without special knowledge.⁵

A removable insert

A removable insert is a snug frame that presses into the window opening. One DIY build uses 2x2 lumber, 2 1/2 inch screws, thick plastic sheeting, hot glue, two handles and weatherstripping half an inch wide by 5/16 inch thick.³ The builder says it "will keep the drafts and bugs at bay, won’t inhibit the functionality of the window" and can add privacy without blocking the light.³

Here's how that build goes:

1. Measure the opening. Hers was 35 inches by 22 5/8 inches.³
2. Cut the two long sides half an inch shorter than the opening.³
3. For the short sides, subtract twice the thickness of your 2x2, then another half inch.³
4. Screw the corners through pilot holes, then glue plastic over both faces so there's an air pocket between them.³
5. Add the handles, then weatherstripping on one short side and one long side. Press it into the opening. It should fit very snug.³

Frosted window cling on the plastic makes it opaque if you want privacy.³

On an egress window, treat the insert like a cover under R310.4.4. It has to come out from inside without a key, a tool or more force than opening the window takes.⁵ Put the handles where a child can reach them. Show everyone in the house how it lifts out. If it takes a hard pull, trim the weatherstripping until it doesn't. Your building department makes the final call on whether it passes.

Rigid foam board, for windows you'll never open

One option for a window you'll never use is to seal it from the inside with rigid foam. In one Green Building Advisor thread, the owner planned 2 inches of polyiso board with the edges sealed by canned spray foam.⁶ An expert member saw no harm in that as a stopgap if the windows were going anyway, and suggested painting the glass first.⁶ Another said the longer-term fix is to take the window out and build a wall-like panel in the opening.⁶ A third, who took out his own basement windows, warned against leaving them in: "If you leave the windows in they will rot, the glass will get damaged and mice and other things will start coming in."⁶

Two limits apply. Never do this to an egress window. And think twice in a room you plan to finish. The 2021 IRC gives habitable rooms glazing of at least 8 percent of the floor area, with at least 4 percent openable, unless mechanical ventilation and artificial light meet the section R303.1 exceptions.⁵ Boarding up a window now can create a problem at inspection later.

Reflective foil and blinds

Reflective bubble foil is sold for windows too. One 23.6 inch by 10 foot roll was $13.99 on Amazon.² It blocks the view and the light. Blinds cost $30 to $200 per window installed.¹ No source we checked measured how much cold either one keeps out, so treat them as light and privacy fixes.

Do window well covers help with cold air?

Indirectly. A well cover keeps debris, rain and snow out of the well while still letting light through.⁴ None of the sources we checked measured its effect on drafts. Over an egress well, the cover has to open from inside without a key, a tool or extra force.⁵ Our window well covers guide compares the types.

Clear polycarbonate covers are popular because they're durable and keep the view. Metal grate covers add security but block more light.⁴ For cold, a solid cover is the one that keeps snow off the glass.

Size matters on an egress well. A cover can't shrink the opening below the code minimums.⁵ Under the 2021 IRC, the window needs a net clear opening of at least 5.7 square feet, at least 24 inches high and 20 inches wide.⁵ The well needs at least 9 square feet of floor area, with at least 36 inches of width and projection.⁵

Water matters more than wind. The code has area wells drain into the foundation drainage system, with an exception for well-drained soils.⁵ HomeGuide puts a drainage system at $1,000 to $4,000.⁴ A well that holds water is a bigger problem than a drafty sash, so fix that first.

When should you replace or close up a basement window instead?

Replace a window when the glass is single-pane, the frame is rotting or the sash won't open and close properly. Close the opening for good only if it isn't an egress window and the room doesn't need its light. Both jobs cost far more than sealing, so price them at an estimate.

HomeGuide lists the signs: cracked glass or a rotting frame, trouble opening or closing, drafts around the window and windows more than 20 years old.¹ Here are the costs it gives:

• Storm windows cost $150 to $400 each installed.¹ They fit over your existing windows and add insulation.¹
• Double-pane windows cost $400 to $2,000 installed.¹ Triple-pane windows cost $450 to $3,000.¹
• Changing the window size needs a permit that costs $50 to $200 for reframing the opening.¹

Replacing an egress window has its own rule. Under section R310.5 of the 2021 IRC, a replacement is exempt from the size rules if it's the manufacturer's largest standard size that fits the existing frame or rough opening. It must also keep the same operating style, or one with an equal or larger opening.⁵

Closing a window for good is a small wall job. An expert on Green Building Advisor said the infill should have "all the same elements as any wall": cladding, a weather-resistive barrier, an air barrier, insulation and interior finish.⁶ Before you close one, remember what it would cost to add it back. HomeGuide puts a new egress window at $6,000 to $8,000 on average.⁴

If the windows are part of a bigger project, get a written quote for finishing your basement and have the windows priced in the same visit. You get a free on-site estimate and a written, itemized quote, and nothing starts until you sign.

What to ask your contractor about basement windows

A good quote lists the window work as its own line items. Ask which windows are egress windows, how each fix keeps them operable and what has to be repaired first. Then check the permit and the well cover. These are the questions to bring to the estimate:

• Which of my windows count as egress windows, and does each fix keep them operable?
• Are weatherstripping and frame sealing listed on the quote?
• If you're replacing an egress window, is it the largest standard size that fits, with the same operating style?
• Will the well cover open from inside without a key or tool?
• Is there rot in the frame or water in the well that needs fixing first?
• Does the job need a permit? Your contractor pulls the permit and books the inspections.

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