Where the draft is coming from
With the window closed on a windy day, hold your hand or a stick of incense near each spot and note which one moves the air:
- Between the sash and the side jambs, or where the upper and lower sash meet in the middle. That's fit and weatherstripping, the easiest fix.
- Around the glass. Cracked or missing putty lets air and water in. The National Park Service's Preservation Brief 9 says loose putty lets water saturate the wood, especially at the joints.
- Around the trim and the wall. That's air sealing between the frame and the house, not a window problem at all.
Also note sash that rattle, a lower sash that won't stay up (usually a broken cord), and paint that blisters or peels in one spot. Brief 9 says paint failure is a clue to where water is getting in, and that the sill, the sill-to-jamb joints, the bottom corners of the sash and the joints of the small glass dividers are where rot usually starts.
Repair, rebuild or replace
Brief 9 sorts wood window work into three levels, and they're useful when you read a contractor's proposal:
- Routine maintenance: some paint removal, taking out and repairing the sash, reglazing, frame repairs, new weatherstripping and repainting.
- Stabilization: partly decayed wood is patched, built up or consolidated, for example with epoxy, and painted.
- Parts replacement: a rotted sill or sash piece is replaced while the rest of the window stays.
A window that only needs the first level is a poor candidate for replacement. Brief 9 also says the source of the water has to be found and fixed before any of these repairs, or the rot comes back. The Park Service's own guidance for historic buildings says repair should be the first option considered, and that hard operation, energy use, code requirements or hazardous materials alone aren't reasons to replace, though they can be weighed alongside real deterioration.
What storm windows actually change
If heat loss is the worry, price storm windows next to replacement. In a Pacific Northwest National Laboratory study, adding a clear glass storm panel over a single-pane window cut its U-factor, the rate of heat loss through the window, by 47 to 53 percent, and a low-E storm panel cut it by 59 to 64 percent. Storm panels also cut air leakage through older windows. That's the window's heat loss, not your whole heating bill, so ask anyone quoting savings what assumptions they used. Whether an energy assessment is worth doing before replacing windows covers how to see where the house really loses heat.
Lead paint applies to both options
In a house built before 1978, assume the window paint may contain lead until testing shows otherwise. EPA's Renovation, Repair and Painting rule requires paid contractors who disturb that paint to be certified firms using trained workers. The small-job exemption covers 6 square feet or less inside per room, or 20 square feet or less outside, but EPA says window replacement is always covered regardless of size. So a replacement crew needs the same lead-safe practices as a restorer. Don't dry-scrape, sand or heat-strip old window paint yourself to see what's under it. What a quote should say about lead-safe work lists what to look for in writing.
Philadelphia historic properties
If your house is on the Philadelphia Register of Historic Places or in a historic district, the City says repairing, removing, replacing or covering windows, including storm windows, needs a Historical Commission project review as part of the building permit. Replacing clear window glass and scraping and painting wood trim don't. The review is free, the City says staff approve more than 90 percent of applications without sending them to the full Commission, and staff can be reached at (215) 686-7660 or preservation@phila.gov. Call before you order windows. How to check whether your Philadelphia house is designated walks through looking it up.
What to ask before you sign
- Which windows need which level of repair, and can you show me photos of the rot on any you want to replace?
- Can you repair one representative window first? The Park Service suggests a sample repair to judge the look, cost and quality.
- Will the price include weatherstripping and storm windows as separate lines?
- Is your firm EPA lead-safe certified, and who tests or treats the paint as lead-based?
- For replacement, does the old frame stay, what trim gets disturbed, and does the new unit match the original pane pattern?