Insert or full-frame: get it in writing
Most replacements are inserts: the new unit slides into the existing frame, which keeps cost and mess down. The Department of Energy's Building America Solution Center points out the catch. Older windows often were never air sealed behind the trim and may have no pan flashing under the sill, and an insert leaves those problems where they are. A full-frame replacement strips the opening back to the framing on all four sides so it can be flashed, insulated and sealed. DOE's checklist calls full-frame the recommended option.
Neither is wrong for every house, but the quote should name which one you're buying. Ask: "What stays, what comes out, and will I be able to see the condition of the opening before the new window goes in?"
What the flashing section should say
For full-frame work, DOE's checklist expects these pieces, and a good quote mentions each:
- A sill pan at the bottom (rigid, flexible or liquid-applied) that runs out to the face of the wall's water barrier, the house wrap or building paper behind the siding.
- Side flashing over the window flanges and the sill pan, tied into that barrier.
- Head flashing at the top that laps over the side flashing, with the house wrap folded down over it, so every layer overlaps like shingles and water runs out instead of behind.
- Installation following ASTM E2112, the standard practice for installing exterior windows, plus the window maker's instructions.
Watch for a quote that promises to seal everything. DOE's checklist says to caulk the head and side jambs but not across the sill, and the Solution Center's window guide says the joint below the frame shouldn't be caulked and factory weep holes in the bottom of the frame shouldn't be filled. Water that gets into the window has to be able to drain out. Ask the installer to show you where sealant goes and where it deliberately doesn't.
Also ask about the metal head flashing over the outside trim. The Solution Center says it should stick out a little past the trim on each side and angle out at the bottom to drip water away. It's usually the only flashing you can see once the job is done.
Inside air sealing is a separate line item
Exterior flashing keeps rain out; it doesn't stop drafts. DOE's checklist has the gap between the window and the framing filled with non-expanding spray foam or blown-in insulation, and on old windows that includes the hollow sash-weight pockets after the hardware is removed. Foam or caulk inside is not a substitute for flashing outside, so the quote should cover both.
Hidden rot, trim and restoration
Full-frame work means pulling trim and sometimes siding. DOE's checklist has replaced exterior trim primed on all six sides and matched to what's there, and interior trim restored to match. Get those, plus painting and disposal, spelled out rather than left to an allowance.
Then ask what happens if opening the wall turns up soft wood or no water barrier at all. The Solution Center shows a house where new windows went in over a rotted sill that was never fixed. A sensible contract says you get photos and a written price for the repair before extra work starts. If framing looks damaged, ask who will judge it and whether a structural engineer is needed.
Before the estimate visit, you can note what you see without opening anything: stains or peeling paint under windows, trim that feels soft when you press it with a thumbnail, bubbling paint on the siding below, and weep holes that have been painted shut. Those clues help, but they don't prove the window is the leak; a roof, gutter or plumbing problem can look the same.
Lead paint in older homes
If the house was built before 1978, EPA's Renovation, Repair and Painting rule applies, and EPA says window replacement is always covered no matter how small the painted area. The firm must be EPA lead-safe certified, and unless testing shows the paint is lead-free, lead-safe work practices apply. That covers most Philadelphia rowhomes and a lot of older Bucks and Montgomery County houses. The quote should say how dust will be contained and cleaned up, and the contractor should be able to show its firm certification.
Permits and historic review
In Philadelphia, the city's building permit page says replacing doors and windows in a one- or two-family home doesn't need a building permit. The exception that catches people is historic designation. If the property is on the Philadelphia Register of Historic Places, the Historical Commission must review window replacement, including storm windows, before work starts. How to check historic designation before exterior work walks through looking it up, and whether storm windows are still worth it on an older house covers keeping the originals instead.
Outside the city, each Bucks and Montgomery County township sets its own rules, so ask the contractor who will confirm permit needs at your address. Why permit rules differ from one township to the next explains where to check.
Before you sign
- Photos of the opened rough opening, sill pan and finished flashing before trim covers them.
- A copy of the installation instructions for the window being installed.
- Written workmanship coverage separate from the manufacturer's product warranty.
- Pennsylvania's required contract terms. What Pennsylvania law requires in a home improvement contract lists them.