DCA6 (Deck) Questions
DCA6 (Deck) Questions
(OP)
I just sent an email to AWC with the following (2) questions:
The overhang of the joist is limited to the lesser of Lo or L/4 (1/4
the backspan) per this document. Where is the L/4 coming from?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
I am looking at Table 2 of the DCA6 (Maximum Joist Spans and Overhangs) I am interested at how the overhang allowable length (Lo) was obtained. Was the 220 lbs point load applied with all other distributed live loads removed? I typically like to manually calculate my deck loads so I would like to make sure that I am checking all load conditions accurately and that they meet or exceed the DCA6 requirements. Another thing I found counter-intuitive are the allowable overhang lengths (Lo) as they vary by joist spacing. It would seem that joists that are spaced closer together (ie. 12" o/c) would have greater allowable overhang lengths. Based on Table 2 this does not appear to be the case.
The overhang of the joist is limited to the lesser of Lo or L/4 (1/4
the backspan) per this document. Where is the L/4 coming from?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com






RE: DCA6 (Deck) Questions
RE: DCA6 (Deck) Questions
I've got a deck with 12' of backspan and a 4' overhang (L/3) so technically it fails, the client is upset because the local bldg. dept. says his deck is a "no-go".
It has 2x8 HF No. 2 joists @ 16" o/c, according to Table 2 of the DCA6 the max. allowable (Lo) overhang is 1'-10", the backspan limit is L/4 or 3", so the Table 2 value governs in this case.
Technically it also fails on the main span @ 12', Table 2 gives an allowable span of 11'-1" for a 2x8 HF @ 16" o/c
I'm also trying to get a feel for what other engineers are doing with deck engineering. Is the DCA6 by the AWC the standard that everyone goes to?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: DCA6 (Deck) Questions
I have always interpreted the DCA6 as a prescriptive code, similar in that regard to the IRC, meaning it's requirements and restrictions apply so long as the structure is not being designed by a licensed Professional Engineer, but if the structure is being designed by a licensed Professional Engineer then I would not expect the building department to overrule the PE's design to enforce a provision like the backspan/4 limit on cantilever length. They may generate a question/comment during their plan review, but then I would expect them to accept a response from you outlining that your structural analysis and design meet the requirements of the IBC as satisfactory.
RE: DCA6 (Deck) Questions
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com