ANSI Standards for Roof Uplifting

General

• As the homeowner, you must consult with a licensed worker such as an architect or civil engineer who is qualified to judge roof structure and wind loads. She must verify that the roof deck and structure can support the installed roofing system, and the fastener design load requirements. Site-pullout tests might be necessary to ensure that the fasteners and deck have enough holding power during winds. Tests are based on the spacing of fasteners either as determined by the ANSI standards or by the spacing required by the tests, whichever is more conservative.

Uplift Loads

• The uplift loads that the roof must meet depend on the building height, the surroundings, the wind speed and the part of the roof being analyzed. For example, a home is up to 30 feet high in an area surrounded by other closely spaced houses of the same height, and subject to peak wind gusts of 90 mph. The uplift loads must be at least 43.3 lbs. per square foot for the roof corners, 28.7 psf for the corners and 17.1 psf for the rest of the roof. Increasing the peak wind gusts to 100 mph increases the required loads to 53.4 psf for the corners, 35.5 psf for the perimeter and 21.1 psf for the field.

Roof Assemblies

• Roof manufacturers generally supply the tested load capacity of any roofing system. Dividing this capacity by the safety factor of two generally yields the factored tested load capacity. This tested capacity must exceed the uplift loads specified by ANSI standards, or the roofing system is not allowed on that particular building. If the factored tested load capacity exceeds the uplift load for most of the roof, but is under the load for the perimeter or corner, installers can use a separate extrapolation method to determine whether the roof is suitable. However, this method requires that the roof has either mechanical fasteners or adhesive beads to attach insulation; the tested wind uplift load capacity has a minimum of three full-sized insulation/cover board/substrate boards on the test frame; and the field load does not exceed 53 psf.

Green Roofs

• In 2010, ANSI adopted standards for vegetative roofing systems, which consists of vegetation and growing media, drainage system and waterproofing over a roof deck. It specifies the maximum wind speeds that a roofing system can tolerate based on roofing system type, building height, surroundings and the distance between the growing media and the top of the parapet. The parapet is the surrounding wall on the roof that keeps the vegetation in place. For example, a house up to 30 feet high in an area surrounded by other houses with a System 1 parapet from 2- to 6-inches high can tolerate a maximum wind speed of 105 mph. For building measuring 30 to 45 feet high, wind speed maximum tolerance drops to 100 mph. For higher winds, green roof systems are not allowed.