Replies

1. 
   DanH | Mar 21, 2013 07:49am | #1

   Did you ask them if they'd accept 2x10, or 16 inch centers?

   (If the code for cantilevers doesn't cover this situation, what DOES it cover?)

2. 
   rdesigns | Mar 21, 2013 10:37am | #2

   If the cantilever will be the support for the wall which, in turn, supports the roof, the code (IRC), Table R502. 3.3(1) shows that 2 x 8 joists on 12" centers could be cantilevered only 18"  with a roof width of 24 feet. Your 2 x 8 @ 24" OC joists would not support much of a load. 

   Will your cantilever actually need to support a bearing wall and roof span? If so, what is the span of the roof section being supported? If you have trusses, it will the the full length of the trusses; if you have a stick-framed roof, it will be the span width from the interior bearing point to the end of the cantilever.

   Considerably longer cantilevers are allowed for those that don't support bearing walls.

1. 
   oops | Mar 21, 2013 08:37pm | #3

   Sorry, but I don't understand.  Are you suggesting that the total load of the span should be considered  when calculating the load on the end of the cantilivered floor joist?  The reaction on the other end of the truss / joist / rafter or what ever can't be zero.   Wouldn't you just consider one half the total load of the span?

1. 
   rdesigns | Mar 22, 2013 09:46am | #4

   Sure, the load on the end of any span, whether roof or floor, will be only 1/2 of the total span. The code table uses the term "roof width" with listed widths of 24', 32' and 40' along with various snow loads. The table assumes that 1/2 of the span will bear on the cantilevered wall.

   However, your original post indicates that you are building a cantilevered deck, and probably the cantilever end won't be supporting a roof above. That's one reason why the inspector said the code doesn't cover your situation. The other reason is that, even if the cantilvered end is supporting a load from above, the code "wouldn't cover it" because 2 x 8's on 24" centers won't meet the code.

   Also, there's another table in the code (R502.3.3.2) that may be more applicable--it is for cantilever spans supporting only an exterior balcony (or, deck, in your case.) Again, however, 2 x 8's on 24" centers are not listed. 2 x 8's on 16" centers are listed to allow a cantilever of 36" with a snow load of less than 30 lbs/sq. ft.

   So, your next question might be: Since my cantilever is only 24", and my snow load is less than 30 lbs/sq. ft., could I be allowed 24" centers on my 2 x 8"s?

   The answer is: Possibly, because footnote "f" on that same table states: "Linear interpolations shall be permitted for ground snow loads other than shown."

   Other than getting an engineered design, you might go over the code table with your inspector to see if he will "interpolate" the table to allow 2 x 8's on 24" centers, or if some other compromise might be acceptable.

1. 
   dirtpour3 | Mar 25, 2013 06:54am | #7

   Interpolation

   Thanks. I'll give it a try.

3. 
   Mike_Mahan | Mar 22, 2013 12:22pm | #5

   Calcs.

   2x8 @ 24" oc will work. See pages 2 & 8 of the attached. I hope you can get them to buy this.

   
1. 
   dirtpour3 | Mar 25, 2013 06:46pm | #9

   Looks good

   It appears you inserted my deck joist parameters? I appreciate it very much.

   w4 = the load bearing ability of the joist? Percent of beam capacity on page 8 is good as long as it's < 100%?

   Thanks for the help.

4. 
   dirtpour3 | Mar 25, 2013 06:50am | #6

   Joists are in place

   Plans examiner accepted the joists as stated and they are installed now. Inspector failed them in the field. 2 x 10s are not an option now.

5. 
   AndyEngel | Mar 25, 2013 11:43am | #8

   See if he'll accept DCA6-09 spans

   http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf

   DCA6-09 is an alternative deck code by the American Wood Council. It's based on the National Design Specifications for Wood Construction, the same document that all the wood construction details in the IRC are based on. I find it to be an extremely useful document, and it's free.

1. 
   dirtpour3 | Mar 26, 2013 06:47am | #10

   American Wood Council

   Thanks for the lead. I will see if they bite.

1. 
   m1roofing | Oct 05, 2014 09:28am | #11

   Resolution?

   dirtpour3, I currently have the exact situation on a deck. What was the outcome / How did you resolve the issue?

   Thanks,

   m1roofing