Carport Size Calculator

Sizing a carport is a packing problem with clearances. It starts from vehicle envelopes: a compact car is roughly 5.5 by 14 feet, a sedan 6.5 by 16, a full size SUV 7 by 17.5, a pickup 7 by 20, and a large motorhome 8.5 by 30 and up to 11 feet tall. Width is the sum of the vehicle widths plus a buffer between each pair and at each outer edge, and 3 feet per gap is the common figure because a front door swings about 30 to 34 inches. Length is the longest vehicle plus front and rear clearance. Height is set by the tallest vehicle plus the depth of the roof structure, with 8 feet a practical minimum, 9 to 10 feet preferred for lifted trucks and roof racks, and 12 to 14 feet needed for recreational vehicles. The structure itself is driven by roof load. Under ASCE 7 the flat roof snow load is computed as 0.7 times exposure, thermal, and importance factors times the ground snow load, and ground values range from zero along the Gulf Coast to well over 100 pounds per square foot in mountain counties. A 22 by 22 foot roof at 20 psf therefore carries roughly 9,700 pounds. Posts are typically spaced 8 to 12 feet apart, footings extend below the local frost depth, and beam size follows the clear span. These are preliminary numbers only. Open sided canopies are frequently governed by wind uplift rather than gravity load, since ASCE 7 treats a free roof as having pressure on both faces, so any permitted carport needs a local code check.

The word carport is generally credited to Frank Lloyd Wright, who used it for the covered parking bay of the Herbert and Katherine Jacobs House built in Madison, Wisconsin in 1936, the first of his Usonian houses. Wright argued that an automobile needed shelter rather than a room, and the open sided structure suited his goal of building genuinely affordable middle income houses. The idea spread quickly through post-war American suburbs, where it cost far less than a garage and worked well in mild climates, before losing ground to enclosed garages that doubled as storage. The engineering basis for sizing them came from separate work on structural loads. American minimum design load requirements were consolidated in ANSI A58.1, first published in the 1940s, which was transferred to the American Society of Civil Engineers and renamed ASCE 7 in 1988. Its snow chapter introduced the ground-to-roof conversion factors, exposure and thermal coefficients, and drift provisions that carport roofs are still checked against, while the wind provisions for open buildings and free standing roofs, which matter enormously for a structure with no walls to resist uplift, were expanded in later editions. Residential permitting was standardized when the International Code Council, formed in 1994, published the first International Residential Code in 2000, consolidating the three regional model codes and setting the thresholds above which accessory structures such as carports require permits and engineering review.