How can I guesstimate U-Factors for older unmarked windows?
I do work legalizing unpermitted dwellings, of which my area has tens of thousands. These were all built at a time when such units were not allowed, so often zero permits. Now, these can become ADU’s (Accessory Dwelling Units) but must generally be brought up to Title-24.
I have a unit with vinyl double hung double pane windows, as inserts into a early 1900’s redwood frames. They’re perfectly good, but I can’t exactly date them, and there’s no real maker mark, and no U-Factor.
Could anyone point to a resource by sale date, of the required minimum U-Factor and SHGC for windows in California USA?
Without this we’ll have to tear the windows out, and frankly there seems to be lower hanging fruit for energy efficiency. I’m guessing it’s carbon negative to rip these out.
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