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Uneven jambs make the replacement size hard to pin down
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When width readings differ at the top, middle, and bottom, how do you tell whether that’s ordinary clearance for the replacement unit or a sign the opening needs attention before anyone orders a window? I’d also measure the height at both sides, but I’m not sure how to interpret the pattern: an opening can be out of square, or a jamb can bow in the middle, and those don’t seem like the same issue.
Is the usual starting point to size from the narrowest width and height, then apply the manufacturer’s specified deduction? How much does that depend on whether it’s an insert or a full-frame replacement, and when would you stop measuring and get the opening assessed rather than trying to account for the unevenness with the order size?
1 reply
The diagonal measurements can help show whether the opening is out of square. If they differ, the corners may not be square; if they’re similar but the width narrows at mid-height, that points to a localized narrowing, not necessarily a bowed jamb. Either way, the pinch point matters for fit, but the measurements alone may not identify its cause.
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