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Old 03-14-2011, 12:08 PM   #1
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deck framing help


Is 2x12 joists 12" OC overkill? I want deck to be super strong and last forever, but this seems like it might be a little extreme with 2x12 joists. My deck is 21' x 35'. I set 2 rows of 6 6x6 posts...1st row is 10' out from house and second row is 20' out from house. I installed double 2x12 beams on 6x6 posts so the spans of joists will be 10'....do I need to install blocking between these spans. I've read that anything over 8' span requires blocking, but I didn't know if this was the case with 2x12's.

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Old 03-14-2011, 12:25 PM   #2
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...I think 2x12 is a little big.10's should be fine.

12"oc is fine. 16"oc will save some money. Sometimes it has to be 12" depending on what decking material you use and what direction you lay it in.

I think 2 rows of blocks. Say at 7' and 14'.

Cant comment on beams. Whats your beam span?

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Old 03-14-2011, 12:35 PM   #3
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beam spans are 6.5 feet. doubled up 2x12's. I have to use 2x12 joists as the 2x12 ledger boards were installed by framing contractor. I'm using 5/4 pressure treated deck boards running perpendicular to the joists...no angle.
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Old 03-14-2011, 12:39 PM   #4
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Then whats your question?
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Old 03-14-2011, 12:41 PM   #5
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mainly I wanted to know if 12" OC was overkill....I used software to design deck, and it spit out 12" OC for joists and I don't think I've ever saw another built like this. It will make it a pain in the ass to install blocking and about $200 - $300 more in lumber. Also, wasn't sure if I needed blocking with my joist sizes and spans.
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Old 03-14-2011, 12:44 PM   #6
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Anything better than minimum Code is safer, stronger, better; http://www.lancova.com/deckinfo.pdf
2009 update; http://www.awc.org/Publications/DCA/...eckarticle.pdf

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Old 03-14-2011, 12:48 PM   #7
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...I allways install blocking.

.. you can still use 2 x 10 joists. Ledger needs to be equal to or greater than deck joists and no greater than band joist.
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Old 03-14-2011, 12:49 PM   #8
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Well put Gary.
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Old 03-14-2011, 12:54 PM   #9
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Thanks for the .pdf file....that is exactly what I was looking for. I love this site.
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Old 03-14-2011, 12:54 PM   #10
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Thanks. I forgot; bridging; http://www.awc.org/Publications/DCA/...eckarticle.pdf
Span; http://publicecodes.citation.com/ico...002_par017.htm

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Old 03-14-2011, 03:34 PM   #11
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2 by 12 at 12 " is overkill. The norm for a 10 ft span is 2 x 10 at 16" spacing. If you want it super stong, 2 by 12 at 16" will probably be just fine.

By the way, we do not know where you are. In this part of the country, if you are not using treated lumber, your frame will start to rot in a few years.

Also, with treated lumber make sure your fasteners are correct for the lumber. Certain treated lumber will corrode certain fastener material in as little as 6 months. I like stainless steel screws, but at $11.00 perpound it adds up!
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Old 03-14-2011, 03:43 PM   #12
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You should check with your local code enforcement official regarding minimum requirements for your deck. My building inspector has a nice 10 page guide that describes pretty much everything you need to know, including minimum beam and joist dimensions, handrails, stairs, posts, connectors, ledgers etc.

You want your deck to be super strong and last forever, but whether it lasts forever is more a function of the types of materials and certain details like flashing, hardware, and connections and less a function of how strong the joists and beams are. For example, you can use 6x6 posts, which are "super strong", but if you install them directly into soil they are going to rot in a few years unless they are ground contact rated. In my town, by the way, all posts are required to be installed on concrete piers, and the piers are required to have a galvanized standoff for the posts. These types of details are going to determine how long your deck lasts. How big the beams and joists are will determine the maximum allowable load on the deck, and will determine how stiff the deck feels, but will have little to do with longevity.

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