Deck Addition - Double my Deck

Old 04-28-10, 10:31 AM
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Deck Addition - Double my Deck

My deck is 12x12. I want to double it to 12x24. Want to keep it simple and use the existing stairs. Right now, the deck is supported on the side of the house and also by two 4x4 posts that support a 4x4 that runs parallel to the house. These hold up the deck. I want my addition to be flush with my current deck. Should I just use four 4x4s to support the new addition and attach to the current deck? Thanks!
Old 04-28-10, 01:30 PM
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Bunch of things come into play. Here, we have to use 6x6's because of the height of decks in the mountains. How high is your deck off the ground? The only other downside I can think of is when you marry the two pieces together, you will have a single line where the decking draws together, rather than a staggered look. If you can live with it, then it is up to you. I would double the joist on the end where you want to start your extension, bolting it in several places with carriage bolts, attach your rim joist to the house using carriage bolts, then complete your rectangle/square, adding internal joisting at 16" oc using joist hangers. The post and beam you have now, should be duplicated on the addition, not only for aesthetics, but firmer support. Your posts should be sitting on Simpson Strontie post bases, which are on top of 12" sonotubes filled with concrete. I know I started from the top down, so just reverse everything I said and you will be OK.
Old 04-30-10, 03:18 PM
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4X4's aren't large enough for the beams, unless the 4X4's are spanning less than 4' between posts. 4X6's will only span 6', and you seem to want to span about 8' to 10' between posts. Use a larger beam. (4X10 or dbl. 2X10's)

Post size is determined by post height. A 4X4 post can't be more than 8' tall. Anything taller than that requires a larger post.

Take all of what Chandler I I have told you with a grain of salt. He's on the right coast and I'm on the left one. Things are totally different depending on where you're at. Best to check with you local bldg. dept. and see just what applies in YOUR backyard, which is where you'll actually be building the deck!

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