Most drafty windows don't need to be replaced. Fix them in order: find exactly where the air gets in, seal the gaps that never move with caulk, weatherstrip the parts that do, and, if the glass is single-pane, add low-e storm windows. Replacement makes sense when the frame or sash is rotted beyond repair, the window won't operate safely, or you're already planning bigger work. In Philadelphia, two rules can change the plan: properties on the Philadelphia Register of Historic Places need Historical Commission review even for windows and storm windows, and in a home built before 1978 any paid window replacement has to follow EPA's lead-safe rules.
This is general information. For code and permit questions, the City's Department of Licenses and Inspections (L&I), or your township or borough in the suburbs, has the final word.
Step 1: Find where the air actually comes in
"The window is drafty" can mean four different leaks, and each has a different fix:
- Between the sash and the frame (the moving parts). Common in old double-hung windows whose sashes rattle in their tracks.
- At the meeting rail, where the top and bottom sashes overlap. If the lock no longer pulls them together, air comes straight through.
- Around the outside of the frame, where the window meets the wall or the trim. This is usually failed caulk or a gap behind the trim.
- Through the glass itself. Single-pane glass feels cold because it loses heat fast, even when it's sealed.
To find the leak, wait for a cold, windy day. Close the windows and doors, turn on the bathroom and kitchen exhaust fans to pull air through the house, then move a strip of tissue or a lit incense stick slowly around each window. Where the tissue flutters or the smoke streams sideways, you've found it. The Department of Energy's building science program at PNNL has a short guide to finding leaks and weatherstripping windows and doors that uses the same tissue test.
Check the lock, too. On a double-hung window, a sash lock that closes loosely, or is missing, leaves a gap at the meeting rail. Tightening or replacing it is often the cheapest fix of all.
Step 2: Fix what you can yourself
Caulk the gaps that don't move
Use caulk where the frame and trim meet the wall, inside and out. Scrape out loose, cracked old caulk first, clean the joint and let it dry, then run one continuous bead. Exterior joints take the most weather, so use a caulk rated for exterior use. Don't caulk a window shut: the sashes have to open, and in bedrooms they may be your way out in a fire.
Weatherstrip the parts that do move
The PNNL guide matches the weatherstripping to the spot:
- Side channels of a double-hung window: tension seals (folded vinyl or spring bronze) that sit inside the track.
- Top and bottom of the sash: adhesive tape, rolled vinyl or reinforced foam.
- Meeting rail: removable putty-type air-sealing cord is a temporary fix you press in each fall and pull out in spring. Interlocking metal strips are the permanent version, and the guide notes they're best installed by a pro.
Remove old weatherstripping first and clean the surfaces so the new strips stick. Afterward, open and close the window and make sure the lock still engages. If it doesn't, the strip is too thick.
Before you scrape or sand anything
Many Philadelphia rowhomes and twins were built long before 1978, and windows are one of the places lead paint survives: on sashes, in the tracks and on the sills, where friction grinds it into dust every time the window moves. EPA's rule for contractors generally doesn't apply to homeowners working on their own home, but EPA's advice for do-it-yourselfers still applies: keep children, pregnant women and pets out of the work area, contain the dust with plastic sheeting, seal off doors and heating and cooling vents, and clean up with a HEPA vacuum and wet wiping. If you'd have to scrape or sand painted wood to get a weatherstrip to fit, that's a good point to hire it out.
Step 3: Consider storm windows before replacement
If your windows are single-pane and basically sound, storm windows are the step most people skip. Modern storms aren't the aluminum panels you hung each fall: they mount permanently over the existing window, outside or inside, and many have a low-emissivity (low-e) coating that reflects heat back into the room.
ENERGY STAR says certified low-e storm windows are an affordable option where full replacement is difficult, and estimates savings of about 10% on heating and cooling bills when they go over single-pane clear glass that has no storms. That estimate doesn't count the air-leak reduction, which ENERGY STAR says adds more savings but varies a lot from house to house. Treat the number as a rough guide; your bills depend on your house and your rates.
Interior storms are worth a look in rowhomes where the front façade matters, in condos, and on upper floors where working from outside means a lift or scaffolding. On a historic property, ask the Historical Commission before you buy either kind (see below).
Step 4: When replacement is the right call
Repair and storms don't fix everything. Replacement is usually the better answer when:
- The sash or frame is soft and rotted, not just weathered. Push a screwdriver into the sill and the bottom rail: if it sinks in easily over a wide area, that wood is failing.
- The window won't stay open, won't close fully or can't be locked, and the hardware can't be repaired.
- Water is getting into the wall around the window, not just air. That points to failed flashing, which needs the window out anyway.
- You're already gutting the room or redoing the façade.
Even then, wooden windows are more repairable than they look. The National Park Service's Preservation Brief 9 on repairing historic wooden windows is written so a homeowner can follow it, and it's a good way to judge whether a carpenter's repair is realistic before you price new units.
Permits for window replacement in Philadelphia
According to L&I's EZ Permit standard for windows and doors (revised June 2026), no permit is required to replace windows in a one- or two-family dwelling if the windows aren't fire-resistance rated and there's no structural change, meaning no change in the location, shape or size of the opening. Making an opening bigger, adding one or changing its shape is a different project and needs a permit.
The same standard lists what replacement windows must meet when the EZ permit applies, and it's a useful checklist for any job: the gap between the new window and the framing must be sealed (caulked, gasketed or weatherstripped), replacement units must have a U-factor of 0.32 or lower, and safety glazing is required in the locations the code treats as hazardous. The U-factor is printed on the window's NFRC label; lower means it holds heat better.
In Bucks and Montgomery counties, the rules are set by each township or borough, so call the code office before you order windows.
Historic properties: talk to the Historical Commission first
If your home is listed on the Philadelphia Register of Historic Places, either on its own or as part of a historic district, the permit picture changes. The Historical Commission's page on getting approval for work to a historic property lists windows, storm windows, doors and storm doors among the exterior features it reviews, while replacing clear window glass counts as maintenance that doesn't need review. L&I's EZ permit route also excludes buildings the Commission lists as historic.
The review costs nothing. Contact staff at preservation@phila.gov or (215) 686-7660 before you sign a contract, and be ready for questions about whether the existing windows can be repaired and whether the replacements match the originals in look and material. Replacing windows on a listed building without review can lead to a violation from L&I.
Lead-safe rules for the contractor
In a home built before 1978, a paid contractor replacing windows must follow EPA's Renovation, Repair and Painting (RRP) rule: the company needs EPA firm certification and a certified renovator on the job, it has to give you EPA's lead-hazard pamphlet before work starts, and it must contain and clean up the dust. EPA says the rule applies to all firms, even sole proprietorships, and window replacement is covered regardless of how small the job is. You can look up certified firms with EPA's lead-safe firm search.
About the federal tax credit
If you've read that new windows earn a federal tax credit, that's out of date for new projects. The IRS says the Energy Efficient Home Improvement Credit (section 25C) is not allowed for property placed in service after December 31, 2025. Windows installed in 2026 don't qualify. Don't let a sales pitch built on that credit rush your decision.
Checklist for drafty windows before winter
- On a cold, windy day, run the exhaust fans and do the tissue or incense test at every window.
- Tighten, repair or add sash locks so the meeting rails close tight.
- Replace failed caulk around the frames and trim, inside and out.
- Weatherstrip the sashes, tracks and meeting rails; check that the windows still open and lock.
- Use lead-safe practices if the job means disturbing old paint, or hire it out.
- For single-pane windows in decent shape, price low-e storm windows.
- Probe sills and bottom rails for rot, and look for water stains on the wall below each window.
- Before ordering replacements, check whether the house is on the historic register, and whether the openings will change size.
- If you hire, ask for the company's EPA lead-safe firm certification for any pre-1978 home.
When to call a pro
Bring in a window or carpentry pro when the wood is rotted, the sash cords or balances are broken, sashes are painted shut, or the fix means scraping old paint in a pre-1978 house. Call one too for any window above the first floor that has to be worked on from outside, for storms or replacements on a historic property (a pro who has dealt with the Historical Commission saves time), and whenever water, not just air, is coming in around a window.
When you get estimates, ask each contractor to say whether they'd repair, add storms or replace, and why; what U-factor the proposed windows have; who handles any Historical Commission review; and how they'll contain lead dust. Our guide on how to check a contractor in Philadelphia covers the state registration and the written contract. If the drafts also chill your pipes, see how to prevent frozen pipes.
On HomeKept you can describe the job once, with photos of the windows and a note on whether the house is on the historic register, and compare up to three estimates from local window and door pros in Philadelphia. It's free for homeowners.
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