DIY measurements can support early budgeting, but they do not replace field verification before ordering. Older openings may be out of square, and trim dimensions are not rough-opening dimensions.
A proper installation includes substrate review, fastening, leveling, drainage, insulation, perimeter seals, and hardware adjustment—not simply placing a unit in the opening.
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Preliminary, field, and order dimensions
Preliminary measurements support budgeting, field verification belongs to the responsible installer, and order size accounts for required installation clearances.
Do not treat outer trim dimensions as unit dimensions or overlook sill slope and wall depth.
Installation joints determine long-term performance
Even a high-performance unit can leak if fastening, leveling, insulation, or exterior sealing is wrong.
Weep holes and exterior drainage paths must remain open rather than being sealed for cosmetic reasons.
Inspect every opening at completion
Check operating force, locks, screens, glass condition, seal continuity, and interior-exterior finishes on every unit.
Save photos of labels, glass markings, written warranties, and scope for future service.