This was a table I saved from an article in JLC some time ago. There's really no reason there couldn't be a prescriptive table.
Hip/Valley Chart2
Hip/Valley Chart2
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2x8 Hip Rafter Failure
- Thread starter jar546
- Start date
jar546
CBO
I have seen that chart. I agree they could probably break it down into a chart but there must be a reason they still have not other than the WFCM 3.28 prescriptively.
RJJ
Co-Founder
That chart has been around for a while. Why the need for a chart? If they submit a plan with calculations and the sizing of the hip in relation to the jack and common rafters is within load requirements either pass it or request a DP's seal.
As much as I hate more pages and tables their purpose is to avoid having to engineer things over and over that have the same solution. It makes common solutions prescriptive. I would rewrite the code language that all hips and valleys need to be designed as supported myself and then reference a table or allow engineering, the current language is pretty murky.
RJJ
Co-Founder
Yes I agree! It always has been. The problem is that unlike common rafters Hips & valleys take on a whole different realm of problems.
example being a Hip with a drop hip just a few feet below it would blow and table. Thus the need for design. Snow loads and drifting can also increase the ability for the hips to fail. The rule of thumb of using one size larger then the rafter size has always had its limits.
As referenced by Jeff the code could allow 2x4 to frame some of the members. Well that IMHO is and would be a mistake.
example being a Hip with a drop hip just a few feet below it would blow and table. Thus the need for design. Snow loads and drifting can also increase the ability for the hips to fail. The rule of thumb of using one size larger then the rafter size has always had its limits.
As referenced by Jeff the code could allow 2x4 to frame some of the members. Well that IMHO is and would be a mistake.
rleibowitz
Bronze Member
Unless I'm mistaken here's how you figure a hip rafter load for a 16x16 building with a total load of 30ft2....8x8x30lbs=1920ibs divided by 2 = 960 pounds of combined live and lead load 12 foot span which is the diagonal of the 8x8 load area...looks to me like a 2x10 does the trick if it complies with 2009 IRC section R802.3 Hip and Valley rafters shall be not less in depth than the cut end of the rafter. Hope this helps