Understanding Duration Of Load Of 1 6 For Roof

Rather the span is based on the rafter s horizontal projection.

Understanding duration of load of 1 6 for roof.

Factor is equivalent to the earlier use of a 1 3 wind load factor in that the newer wind load provisions of asce 7 98 include separate consideration of wind directionality by adjusting wind loads by an explicit wind directionality factor kd of 0 85. Full time loading floor joists serves as the benchmark value. The factor for dead load 1 2 is lower than the factor for live load 1 6 because dead load is more predictable than live load. In order to stay intact and in place a roof must be able to resist loads both permanent and temporary that are pushing.

So consider a simple gable roof on a 24 foot wide ranch framed with 2 6 exterior walls and a 1 1 2 ridge. Anything hung from or attached to the structural framing is a collateral dead load. How long will the members be loaded. See figure 1 headers.

Where l r shall not be less than 12 psf and not more than 20 psf. L r l o r 1 r 2. Benchmark values are multiplied by 1 15 to yield snow load values and by 1 25 for 7 day loading. Tables automatically handle this adjustment.

Since the wind load factor of 1 3 included this effect it must be adjusted to 1 5 in. This is the horizontal distance from the inside surface of the supporting wall to the inside surface of the ridge board. Greater than 10 years 0 9 permanent 10 years 1 0 normal floor ll 1 year 1 075 long term temporary load 2 months 1 15 snow load 7 days 1 25 roof live load 10 minutes 1 6 wind or seismic load less than 2 seconds 2 0 impact load e g. Dead loads consist of the weight of the building itself plus the weight of all fixed items like walls roof and carpeting.

The span would be 11 5 3 4. Roofs are under a lot of pressure. Using lrfd lc 2 the combined design load equals 1 2 times the dead load plus 1 6 times the live load or 15 6 kips. Load limits on the roof of a building.

All loads are listed as pounds per square foot of horizontal projection footprint area. Don t worry about the calculations. In commercial or industrial buildings for each floor or portion thereof designed for live loads exceeding 50 psf 2 40 kn m 2 such design live loads shall be conspicuously posted by the owner or the owner s authorized agent in that part of each story in which they apply using durable signs. It shall be unlawful to remove or deface such notices.

Roof live load reduction. Static loads also known as dead loads are the permanent loads of the structure. Here each square foot of roof system delivers 50 pounds of live load and 15 pounds of dead load 65 psf total to the structural support system. Roof live load may be reduced by the following equation.