Window Permit Glossary

Plain-language definitions for terms you'll encounter when researching window permits, egress requirements, and energy codes.

A–C

Air Leakage (AL): Reported on the NFRC label. Measures how much air passes through a closed window (cfm per square foot). Maximum 0.3 cfm/ft² in most codes. Lower is better.
Building Permit: Official authorization from a local government allowing specific construction or renovation work. Required for most structural changes and egress windows.
Certificate of Appropriateness (COA): Approval document issued by a Historic Preservation Commission confirming that a proposed exterior change is consistent with a historic district's character. Required before a building permit in designated historic districts.
Certificate of Completion: Document issued after a successful final inspection confirming the permitted work is complete and compliant. Keep permanently with home records.
Climate Zone (IECC): One of eight geographic zones (1 = hottest, 8 = coldest) used by the IECC to set energy code requirements. Your county determines your zone.

Egress Window: A window in a sleeping room that serves as an emergency escape and rescue opening. Must meet IRC R310 minimum dimensions: 5.7 sq ft net clear area, 24" height, 20" width, 44" max sill height.
Florida Product Approval (FPA): Florida Building Commission certification required for all windows installed in Florida. Separate from NFRC; verifies wind resistance and product compliance.
Header / Lintel: A horizontal structural member spanning a window or door opening, transferring the load above to the surrounding framing. Must be properly sized for the opening width and load conditions.
HVHZ (High-Velocity Hurricane Zone): Designation for Miami-Dade and Broward counties in Florida where all window replacements require permits and Miami-Dade NOA product approval.
IECC (International Energy Conservation Code): Model energy code published by the ICC and adopted (with amendments) by most states. Sets minimum U-factor and SHGC requirements for windows by climate zone.
IRC (International Residential Code): Model building code for one- and two-family dwellings. Adopted by all 50 states in some form. IRC Section R310 governs egress window requirements.

Like-for-Like Replacement: Replacing a window with the same size in the same rough opening without structural change. Generally exempt from permit requirements in most jurisdictions.
Low-E (Low-Emissivity) Glass: Glass with a microscopically thin metallic coating that reflects infrared radiation, reducing U-factor and (in some configurations) SHGC. Standard in code-compliant replacement windows.
Net Clear Opening: The actual unobstructed open space when a window is fully opened, measured at the narrowest point. What IRC R310 egress requirements are based on — not the window frame or rough opening size.
NFRC (National Fenestration Rating Council): Independent organization that certifies and labels window energy performance. The NFRC label on every window shows whole-window U-factor, SHGC, VT, AL, and CR — what inspectors check for code compliance.
NOA (Notice of Acceptance): Miami-Dade County product approval document, required for all products installed in the High-Velocity Hurricane Zone. More stringent than standard Florida Product Approval.

Rough Opening: The framed hole in the wall into which a window is installed. Larger than the window's nominal size to allow for shimming and leveling. Not the same as net clear opening.
SHGC (Solar Heat Gain Coefficient): Fraction of solar radiation that passes through a window as heat. Ranges 0–1; lower = less solar heat gain. Required to be ≤0.25 in IECC Zones 1–3; no requirement in Zones 4–8.
Sill Height: The distance from the finished floor to the bottom of the window's net clear opening. IRC R310 requires maximum 44 inches for egress windows.
U-Factor: Rate of heat transfer through the entire window assembly (glass, frame, spacer). Reported as BTU/hr·ft²·°F. Lower = better insulation. Primary metric regulated by IECC energy codes. Whole-window U-factor (from NFRC label) is what code requires — not center-of-glass U-factor.
Window Well: An excavated and lined area outside a below-grade window, providing clearance for egress. IRC requires minimum 9 sq ft horizontal area (36"×36") and a ladder if the well is deeper than 44 inches.
WPI-8 Form: Texas Windstorm Insurance Association certificate of compliance required for window installations in TWIA coastal counties. Documents windstorm compliance for insurance purposes.