Allowabla Deflection Attic Floor

Roof rafters roof joists and roof beams.

Allowabla deflection attic floor. This sets an allowable first floor live load of 40 psf a dead load of 10 psf and a deflection of l 360. Plaster or gypsum board. If the span of the joists is 10 feet between supports then the deflection should not be more than 1 3 between the center and the end. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360.

If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. My calculations tell me assuming 2 southern yellow pine joists which are common in my area that 2x6s 16 inches on center will span 9 feet 9 inches with allowable deflection being the governing factor. You can also use the wood beam calculator from the american wood council website to determine maximum rafter and joist lengths. The dead load on a floor is determined by the materials used in the floor s construction.

The l 360 standard means that the floor should not deflect more than the span divided by 360. Use the span tables below to determine allowable lengths of joists and rafters based on size and standard design loads. For this example i ll use the icc which serves as the model for many state and local codes. It defines a live load deflection limit of l 360 for these trusses.

But you can still double the capacity of the existing 2x6s in the attic floor so first let s make sure that s enough for your situation. Other than plaster or gypsum board. Floor live load deflection limits for room in attic trusses deflection limits for trusses with habitable spaces differ depending upon the building code. Other than plaster or gypsum board.

Plaster or gypsum board. First check the local code for allowable live load dead load and deflection see figure 2. See the table below. If there s wall board covered ceiling suspended from the underside of that floor the dead load increases to about 10 pounds per square foot.

Frequently there is misunderstanding regarding deflection between joists. A typical wood frame floor covered with carpet or vinyl flooring has a dead load of about 8 pounds per square foot. Table r502 3 1 1 shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with section r311 7 provided that the design live load does not exceed 30 pounds per square foot 1 44 kpa and the design dead load does not exceed 20 pounds per square foot 0 96 kpa. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.

Floor beams floor joists and floor.