U-Factor
A measure of how well a window or door prevents heat transfer. Lower U-factors indicate better insulating performance.
Why It Matters for Homeowners
Why it matters: U-factor is the metric your contractor uses when ordering windows that pass Title 24 inspection in California. It is essentially the inverse of R-value: lower numbers mean better insulation. The Title 24 ceiling for residential windows in LA climate zones is typically around 0.30, and meeting that level is what the city plan-checker verifies before signing off on a permit.
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