Vent Terminal Height, Frost Closure, and Location (IPC 903)

HEIGHT (903.1): 6 in above the roof or 6 in above the ANTICIPATED SNOW, whichever is greater -- 18 in of snow makes it 24, not 6 -- and 7 FT where the roof is used for anything but weather protection. FROST CLOSURE (903.1.1): where the 97.5% design temperature is 0 degF or less the extension must be at least 3 in, and the increaser must sit at least 1 ft INSIDE the thermal envelope, which is the part everyone misses -- a fitting made up in a cold attic frosts shut exactly like the small pipe it replaced. LOCATION (903.2): never directly beneath, and not within 10 ft horizontally of any door, openable window, or air intake -- of this OR AN ADJACENT building -- unless it is 3 ft above. Vent SIZE from fixture units is separate.

required height = 84 in where the roof is used for a purpose other than weather protection, otherwise max(6 in, snow accumulation + 6 in); frost closure applies when the 97.5% outdoor design temperature <= 0 degF, requiring diameter >= 3 in and any size increase made >= 12 in inside the thermal envelope; location passes when the terminal is >= 10 ft horizontally from a door, openable window, or air intake OR >= 3 ft above it.

IPC 903.1 (vent terminal height, with the 7 ft case for a roof used for other purposes), IPC 903.1.1 (frost closure), and IPC 903.2 (vent terminal location relative to doors, openable windows, and air intakes of the building or of an adjacent building).

All three are short prescriptive provisions reproduced in state and municipal adoptions and code-viewer sites. No table is reproduced; the snow accumulation and the design temperature are local figures entered by the user.

Estimate. AHJ and licensed professional govern.

Field names used by the API: height_above_roof_in, snow_accumulation_in, roof_other_use, design_temp_f, vent_diameter_in, increase_inside_envelope_in, horizontal_to_opening_ft, height_above_opening_ft, required_height_in, height_deficit_in, min_diameter_in, min_increase_depth_in

• Height 6 in above the roof or 6 in above anticipated snow, whichever is greaterIPC 903.1
• Roof in use 7 ft where the roof serves any purpose other than weather protectionIPC 903.1
• Frost trigger 97.5% outdoor design temperature of 0 degF or lessIPC 903.1.1
• Frost sizing not less than 3 in, with the increase made not less than 1 ft inside the thermal envelopeIPC 903.1.1
• Location 10 ft horizontally, or 3 ft above, from a door, openable window, or air intake of this or an adjacent buildingIPC 903.2
• Not checked vent size from fixture units, the branch below, flashing, wall terminations, fuel-gas ventingstated scope limit