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May 2024 #16298 Page #104
Minimum Uniformly Distributed Live Load For Habitable Attics
By MiTek Staff
n attic truss with 7 feet room height – should it be designed for 20 psf (pounds per square foot), 30 psf, or 40 psf room live load?
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Per International Residential Code (IRC) Table R301.5, the minimum uniformly distributed live load for uninhabitable attics with limited storage is 20 psf, for habitable attics and attics served with fixed stairs and sleeping areas is 30 psf, and areas others than sleeping areas is 40 psf. IRC defines Habitable Space as a space in a building for living, sleeping, eating, or cooking. A habitable space has a minimum height of 7 feet and an occupiable floor area not less than 70 square feet with minimum 7 feet in any horizontal dimension (except kitchens). Portions of the room with a sloping ceiling measuring less than 5 feet or a furred ceiling measuring less than 7 feet from the finished floor to the finished ceiling shall not be considered as contributing to the minimum required habitable area of that room. For rooms with sloped ceilings, the required floor area of the room shall have a ceiling height of not less than 5 feet and not less than 50 percent of the required floor area shall have a ceiling height of not less than 7 feet.
The criteria listed here applies to ‘attic’ spaces. These spaces generally have a room profile that follows the top chord/rafter with a center section of uniform height under the collar tie (as shown in the drawing). Attic trusses with a room height 7 feet and above, meeting code requirements of Continued next page
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