A cracked storm window can let in drafts, rain, and bugs, but replacing it doesn’t always mean replacing the main window behind it. In many homes, the storm unit is a separate outer layer that can be removed and swapped on its own. The key is to identify what kind you have, measure carefully, and install the new unit without blocking the drainage paths that keep water from collecting around the frame.
Table of Contents
First, identify the storm window you need to replace
Storm windows sit outside or inside your primary window. They add a layer of protection and can help reduce drafts, noise, and heat loss. Before you buy a replacement, check how the existing unit is attached and whether the damage is limited to one part.
Exterior storm windows
Exterior storm windows are mounted on the outside of the house. Many newer models have aluminum frames and slide in tracks, so you can raise, lower, or remove a sash for cleaning. Others are fixed in place and held to the window trim with screws.
Look for screws along the frame, sliding tracks at the sides, and small drainage openings near the bottom. Those details help you work out how the unit comes off and what features the replacement needs. If the frame is sound but a sliding panel or screen is damaged, you may only need to replace that part.
Interior storm windows
Interior storm windows attach to the room-side of the main window. Some use clips or screws; others are held in place with compression seals or magnetic strips. They’re often designed to fit one specific opening, so measure the frame where the storm unit sits—not the outside trim.
Storm sash versus the whole frame
A storm sash is the movable or glazed section of a storm window. If only the glass, screen, or sash is damaged, replacing that piece may cost less and require less work than removing the entire frame. But if the frame is bent, loose, badly corroded, or no longer seals against the house, replacing the complete unit is usually the more dependable fix.
| What you have | What may need replacing | What to check |
|---|---|---|
| Sliding aluminum storm window | A sash, screen, or complete frame | Track shape, panel size, frame condition, and drainage openings |
| Screw-mounted exterior storm window | Usually the complete frame or a glazed panel | Screw locations, mounting surface, and old caulk |
| Interior storm panel | A panel, seal, or full interior unit | How it attaches and whether the opening is square |
| Wood storm sash | The sash, glass, or entire storm assembly | Rot, loose joints, glazing condition, and paint hazards |
Gather tools and prepare the work area
For a typical screw-mounted storm window, you’ll likely need a tape measure, screwdriver or drill, utility knife, putty knife, gloves, safety glasses, and a stable ladder if you’re working above ground level. Keep a helper nearby for a large unit. Storm windows can be awkward to hold even when they aren’t especially heavy.
Buy the replacement only after you’ve confirmed the mounting style and taken measurements. Bring photos of the old unit, including its corners, tracks, fasteners, and drainage holes. A supplier can use those details to help identify a compatible frame or sash.
If the home was built before 1978 in the United States, old painted surfaces may contain lead. Scraping or sanding them can create hazardous dust. Don’t disturb peeling paint casually; check local guidance and use a lead-safe professional if the work could damage old paint. Also, never lean out of an upstairs window to reach the exterior. Use proper access equipment or hire a window professional.
Measure the opening before ordering
Measurements are one of the most common reasons a replacement storm window doesn’t fit. Measure the place where the new unit will actually sit, following the replacement maker’s instructions. The outside trim size and the storm-window opening are not always the same.
- Measure the width in three places: near the top, at the middle, and near the bottom of the opening.
- Measure the height in three places: at the left side, in the center, and at the right side.
- Use the smallest measurement in each direction when the opening isn’t perfectly even, unless the manufacturer gives a different measuring method.
- Check the mounting surface: note whether the unit fits inside a recess or attaches to flat exterior trim.
- Record the frame depth and attachment details: include track shape, screw positions, and any special corners or flanges.
For example, if the width measures 35 7/8 inches at the top, 35 3/4 in the middle, and 35 13/16 at the bottom, don’t order a 35 7/8-inch unit based on the widest point. The opening narrows in the middle. Follow the supplier’s sizing rules so the frame has the clearance it needs to sit straight without being forced.
Don’t assume every manufacturer uses the same allowance for fitting. Some storm windows are made to a precise opening size; others require you to subtract a small amount. Confirm the method before placing your order.
How to replace a screw-mounted storm window
1. Remove the old unit carefully
Open or remove any movable sashes and screens first if the design allows it. This makes the frame lighter and easier to control. Support the frame with one hand or ask a helper to hold it, then remove the screws around the perimeter.
If paint or caulk is holding the frame to the trim, score the seam gently with a utility knife. Work slowly so you don’t gouge the siding or damage the main window. Once the fasteners are out, ease the frame away from the house. Don’t yank it; a stubborn section may still have a hidden screw or a bonded strip of sealant.
2. Inspect and clean the mounting surface
With the old frame off, check the trim for soft wood, loose paint, gaps, or signs of water damage. A new storm window won’t seal well over rotten or uneven trim. Repair the mounting surface before continuing, and let any filler, paint, or sealant cure as its instructions require.
Remove loose debris and old caulk that would stop the replacement frame from sitting flat. Avoid scraping aggressively if the paint may contain lead. The goal is a clean, stable surface—not bare wood at any cost.
3. Dry-fit the replacement
Hold the new frame in place before adding sealant. Check that it sits evenly, lines up with the opening, and doesn’t bind against the main window. Use a level to check that the sides are vertical and the top is level. If the frame rocks or leaves a large uneven gap, stop and recheck the measurements and mounting surface.
Dry-fitting matters because once you drive screws through the frame, correcting a bad position becomes harder. It also helps you confirm that the sliding panels and screens will move as intended.
4. Apply sealant where the instructions call for it
Some exterior storm windows need a bead of suitable exterior sealant behind the top and sides of the frame. Many designs leave the bottom unsealed or rely on built-in weep holes so rainwater can drain out. Sealing every edge can trap water behind the frame and encourage rot or corrosion.
There isn’t one caulking pattern that fits every product, so follow the window maker’s directions. Keep any drainage slots clear. If you’re installing an interior storm panel, use the supplied gasket or sealing method rather than automatically applying exterior caulk.
5. Fasten the frame without twisting it
Set the frame in position and start the screws loosely. Check alignment again, then tighten the fasteners gradually, moving from one side to the other. Don’t overtighten: pulling screws too hard can bow a thin aluminum frame and make the sash stick.
Test the sliding panels and screens before finishing. They should move without scraping or jumping out of their tracks. If they bind, loosen the frame screws slightly and check whether the frame has been pulled out of square.
6. Finish the edges and test for leaks
Install any sashes, screens, caps, or trim pieces that came with the unit. Seal the areas specified by the instructions, but leave drainage openings open. From indoors, check for visible gaps around the frame. On a dry day, you can also inspect the outside after light rain to see whether water drains away rather than sitting at the bottom.
Replacing a sliding panel or storm sash
If the frame is in good condition, replacing just the sash may be straightforward. Raise or lower the panel to the position that lets it clear the track, then release the tabs or tilt it inward if the design allows. Some units use hidden clips or specific removal positions, so check the manufacturer’s instructions rather than forcing the panel.
Match the replacement panel to the original system. The frame thickness, glazing type, screen arrangement, and track dimensions all matter. A panel that looks close but is too thick or too narrow may not lock, seal, or stay in place safely.
For cracked glass, be especially cautious. Glass can break further while you remove it, and older storm windows may use glazing compounds or fasteners that are difficult to handle. If the glass is large, the frame is high up, or you’re unsure how it’s secured, have a glass or window professional replace it.
Common mistakes to avoid
- Measuring the trim instead of the fitting opening: This can leave you with a unit that won’t mount correctly.
- Ordering by appearance alone: Similar-looking storm windows can use different tracks, fasteners, and frame depths.
- Caulking the drainage path: Water needs a way out of many exterior storm-window assemblies.
- Overtightening screws: A distorted frame can make panels stick and weaken the seal.
- Ignoring damaged trim: A new frame can’t make rotten or loose wood a reliable mounting surface.
- Working at height without a safe setup: If you can’t reach the window securely, get professional help.
When to hire a professional
A handy homeowner can often replace a small, screw-mounted storm window at ground level. Consider hiring a window installer if the unit is large, difficult to reach, custom-shaped, or attached to damaged trim. Professional help is also sensible when you see significant wood rot, suspect lead paint, or need a precise replacement for an unusual historic window.
Getting the fit right can take more time than the installation itself. A professional may be worth the cost if a wrong-size order would be expensive or if water has already damaged the surrounding wall.
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Frequently Asked Questions
Can I replace a storm window without replacing the main window?
Yes. Storm windows are separate units in many homes, so you can often replace the storm frame, sash, or panel while keeping the primary window. Check that the main window and its trim are in sound condition first.
Should I caulk around the entire storm window?
Not automatically. Some models call for sealant along the top and sides while leaving the bottom open for drainage. Follow the product instructions and keep weep holes clear so water doesn’t collect behind the frame.
Can I replace only the glass in a storm window?
Often, yes, if the frame is straight and in good shape. The glass must be the correct size and thickness, and it needs to be secured using the frame’s intended method. Large, cracked, or hard-to-reach panels are best handled by a professional.
How do I know whether I need a new frame or just a new sash?
Replace only the sash if the frame is firmly attached, undamaged, and still holds the panel securely. Replace the full unit if the frame is bent, corroded, loose, badly sealed, or damaged in a way that prevents a proper fit.
Conclusion
Replacing a storm window starts with identifying the type of unit and measuring the actual fitting opening—not guessing from the trim. Remove the old frame gently, repair the mounting surface, dry-fit the replacement, and follow the manufacturer’s directions for fastening and sealing. Pay special attention to drainage and safe access. A carefully fitted storm window can protect the primary window and help keep drafts and rain outside where they belong.
