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Decking beams and joists for perpendicular decking

Gary Cornelisse

Gary Cornelisse

Registered User
Joined
Apr 24, 2017
Messages
2
Location
PA
I'm planning to lay my decking perpendicular to the house instead of parallel. I've been through the DCA 6 several times, and despite what our local code officer said, it's not clear how to figure out the specs for my beams and joists. Table 3 in the DCA is for joists framing from one side only. If my beams are extending from the ledger and I'm running joists between the beams (parallel to the house), it has to be framing from two sides of the beams.

I was hoping someone could point out the relevant sections of the DCA or help me figure out the necessary spec to meet code requirements.

- Basic deck dimensions are 20'x40', 40' side against the house
- Beams and joists will be 2"x10" Southern Pine
- 6"x6" posts at 10' and 20' from house

- 2 or 3 - 2"x10's" for a beam?
- Spacing (joist spans) between beams?

Any help is appreciated. Thank you!
 
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Gary,

Another Welcome to The Building Codes Forum !

On Page 19 and following; of the DCA 6 Guide, it lists the span
distances........Also, the American Wood Council ( AWC ) has an
online calculator for use in determining the correct spans for each
wood species and size of joists used.

Here is a Link to the AWC:
http://www.awc.org/codes-standards/spantables

At the top of the page are the Links to the calculators for use
and the span tables.

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You are going to need piers and posts at the house if you are running the beams perpendicular (or bear on the existing foundation)....so you can run the joists parallel...so you can run the decking perpendicular....
 
I think he's trying to get yellow highlighter out of an old code book!:eek:
 
Saturn2020 said:
, is there any difference if the decking is laid perpendicular or parallel?
Click to expand...
As long as you honor the span limits of the product and adjust the joist spacing as needed, the choice of direction is cosmetic. If you’re on a budget, normal 5/4”x6 deck boards will be the least expensive, followed by 2x boards.
 
There are a number of things to respond to.

1) Where the beams bear their concentrated load at the house, you cannot transfer this load through a ledger attached with any prescriptive means (IRC or DCA-6). Those concentrated loads are not accounted for. In this design you essentially do not have a ledger. You will need to either have a connection engineered or extend the beams into your house and bear them with support directly below (stud post or foundation). FLASH THIS LIKE YOU HAVE NEVER FLASHED BEFORE!! INSANE DETAILING AND CARE. You also need to be sure you have significant lateral restraint at the house at each beam, as you have no ledger fasteners providing this resistance.

2) The reason you cant support the beam from both sides is simply because the engineering in the span table does not account for this. There is a way to do this, but it is outside of the code. It does meet the intent of the code, however. See my course Down the Load Path at www.buildingcodecollege.com for details. You can take the course fro free without the coupon code "welcome" If you are building a deck, I suggest you purchase the other three deck courses as well (if you find the free one of value).

3) There would be nothing unusual about your joist span in this design.

4) You absolutely must understand that you are undertaking a much more difficult design and project with beams/joists in this orientation. This is not recommended for non-studied DIY'ers. It most certainly can be done, but I caution you that what you are intending is not very standardized.

I hope this helps.
 
Mick is a senior and recovering from heart surgery, think he isn't a candidate for avoiding crowds?
 
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