Window-to-Wall Ratio Calculator

This calculator finds the window-to-wall ratio (WWR) for a building facade and checks it against the ASHRAE 90.1 maximum allowed for the declared climate zone. Window-to-Wall Ratio is simply Total Window Area divided by Total Wall Area, expressed as a percentage -- raising Total Window Area raises the ratio, and raising Total Wall Area lowers it, since wall area sits in the denominator of that division. ASHRAE Climate Zone plays no part in that division at all: it only sets Max Allowed (Code), the ceiling the ratio gets compared against, using a simplified three-tier rule -- zones 1 through 3 (hot climates) top out at 40%, zones 4 and 5 sit at 30%, and zones 6 through 8 (cold and subarctic) drop to 25%.

Code Compliant just flags whether the computed ratio clears that ceiling or not. Energy Penalty estimates the extra heating and cooling load implied by exceeding the limit, scaled at 1.5% of extra load for every percentage point over the ceiling, and it sits at zero whenever the design already passes. This tool is a simplified compliance screen for early design, not a substitute for a full ASHRAE 90.1 envelope trade-off study, which also weighs U-factor, SHGC, and orientation together rather than glazing area alone.