Structural & systems · Glossary
U-factor
Also called: U-value
U-factor is the measure of how much heat flows through a window assembly per square foot per degree of temperature difference. Lower U-factor means better insulation. California Title 24 typically requires U-factor below 0.30 for new and replacement windows in single-family residential renovation.
Why this matters for renovation projects
U-factor shows up on permits, contracts, or estimates that Renology covers across LA, San Diego, San Francisco, Seattle, Portland, and Denver. Most homeowners encounter the term once a project is already mid-flight, when there is no time to learn its mechanics without slowing the contractor. Knowing what it means before signing the contract is the difference between a clean project and an avoidable surprise. For how Renology calibrates cost ranges against permit valuations and contractor invoices, see the methodology.