Four questions, one verdict. Identify the frame — vinyl, aluminum, wood, or fiberglass-composite — before you put the wrong cleaner on it.
Verdicts cite Tony Petruzzi's frame-substrates piece (AAMA CW-10, EPA RRP rule, Aluminum Association TB-AC-103).
QUESTION 1 OF 40% COMPLETE
When was the home built or the windows last replaced?
whichever is more recent
Era is the strongest single predictor of frame substrate. Vinyl was uncommon before 1990; aluminum dominated mid-century residential; fiberglass-composite is largely post-2010. If the home is old but the windows were swapped recently, the install year is what matters here.