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I have an old cedar deck, and most of the decking and vertical support posts are rotted out. I'd like to rebuild the deck as-is, just replacing the rotting pieces.

The current design is as follows:

  • 2x8 treated ledgers anchored to concrete foundation
  • 2x8 treated joists coming off the ledgers
  • 2x8 treated rim joists around the edges
  • 4x4 cedar posts around the edges (4 foot intervals), sitting on concrete footings
  • Posts are notched and are supporting the rim joists, attached with nails
  • There are no other supporting posts or beams
  • Deck extends about 8 feet out from the house
  • Deck is about 4 feet off the ground for one section, and 2 feet off the ground for the other section
  • Deck is located in Texas, so snow is not a concern

My concern is that all the information I've found on decks shows people using 6x6 posts as the main supporting structure, with beams on top of those and joists on top of the beams. I only see 4x4 posts used to form the supports for the railings.

I'm hoping to use the current design, and replace all of the posts, decking, and railings. The only significant change I have planned is to attach the posts to the rim joists using carriage bolts instead of nails. Is it reasonable to have 4x4 posts as the primary support, or do I need to consider more significant design changes?

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how high of the ground will the deck be ie How long will the supporting columns be? Do you get a lot! of snow where you are? Some worthwhile reading (IMHO): Heavy Timber Construction - WCD5 - American Wood Council <-- Direct link to PDF). –  Mike Perry Aug 5 '11 at 17:15
    
Sorry I forgot to include that info - it's there now. –  Charlie Aug 5 '11 at 18:12

3 Answers 3

up vote 6 down vote accepted

Around here, 4x4s are not uncommon. This table shows that a 4x4 pine post that is 6 ft or shorter can support a load area of up to 10 ft² assuming 50 lbs/ft².

Don't trust me or a random table on the internet; make our own calculations from tables in the building code or other trusted sources and consider having them checked by an engineer.

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I recommend going to one of the big box stores and buying a book on building decks. I bought one a couple of weeks ago and it had a section on updates to building code.

I do remember that one of them now is that you either need to double up your 4x4's or use 6x6's.

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4x4 post will be fine. I have built many decks for new homes with them. 6x6 is more sturdy of course and will not twist as easy, but for structure purposes, 4x4 will be fine. I would just not go more then 10' apart with them.

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2  
"4x4 post will be fine" how can you (or anyone else) say that, when we don't know the height on the deck ie The length of columns (or if we need to take into account something "snow" loading)? –  Mike Perry Aug 5 '11 at 17:19
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you're missing my point, we currently don't know how high off the ground the deck is, or if something like "snow" loading needs to be taken into account... To make a blanket statement like "4x4 post will be fine" without first knowing all the "important" facts seems at best a little risky to me (IMHO). –  Mike Perry Aug 5 '11 at 17:40
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ok, whatever, first sorry Charlie I did not know my answer was going to upset Mike here, so sorry to argue on your post; however, if you want to park a truck on your deck and it is 6-8ft off of the ground you can use 4x4 post 10' apart and it will be fine and up to code. anything higher and parking a truck use 6x6's wow! –  lazoDev Aug 5 '11 at 17:50
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Sorry I neglected to specify the height - I had included it originally and then accidentally removed that when I reformatted the question. The deck is about 4 feet high. –  Charlie Aug 5 '11 at 18:12
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@lazoDev, your answer didn't upset me & I wasn't arguing with you. I was only making a (valid) point. I could have simply "down voted" your answer, but I don't believe in doing that "blindly" eg Not leaving a valid comment, reason with a "down vote". Your answer was "valid", but dependent on the "missing" information... –  Mike Perry Aug 5 '11 at 20:24

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