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Old 09-14-2010, 09:33 PM   #1
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Deck footing sonotubes


I am designing a 34' x 12' deck (about 400 sq/ft subtracting chimney space). One half is attached to the house by a ledger, the other half is cantilevered on a beam 10' out. It's supported by 6x6 posts 6'6" apart with a 9" cantilever on the ends. That makes 5 sections. I have been reading up on footing sizes and calculated as follows:

400/2 = 200 sq/ft
200 x 40 psf load = 8000 lbs
8000 lbs / 5 sections = 1600 lbs per section.

Various internet charts recommend 16" round footings for this load. The depth is going to be 36". I don't know what kind of soil I have, I'd guess somewhere between loam and clay.

Deck height is less than 3'.

Question:

Using 16" Sonotubes is going to be a whole cubic yard of concrete for 6 footings. Does sound right?

40 psf seems very high. If I understand this right, that's the equivalent of over fourty 300lb persons standing on my 400 sq/ft deck!? The deck itself can't weight more than 3-4000 lbs.

Please forgive my MS paint sketch :



Last edited by kwerk; 09-15-2010 at 09:56 AM.
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Old 09-14-2010, 09:40 PM   #2
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Deck footing sonotubes


Draw it to this: http://www.lancova.com/deckinfo.pdf http://www.soundfootings.com/pdf/US_...t_DepthAVG.pdf
before you get a permit.

Gary

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Old 09-14-2010, 09:46 PM   #3
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Deck footing sonotubes


I already have a permit, they didn't require a plan or anything. The nearest city that DOES has deck codes recommended I dig them to 36". Just seems like an awful lot of concrete.

The IRC2009 only talks about footings for buried posts but I want the post above grade on an adjustable bracket.
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Old 09-14-2010, 09:54 PM   #4
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Deck footing sonotubes


I can do 36" easy....as long as I don't hit ledge
Mine are over 40" down...very close to 44" when fully graded
And once the "pad" under the deck is poured they may be 48" down
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Old 09-15-2010, 06:51 AM   #5
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Deck footing sonotubes


Quote:
Originally Posted by kwerk View Post
Question:

Using 16" Sonotubes is going to be a whole yard of concrete for 6 footings. Does sound right?
Can't help with the other questions, but the size of your 6 piers are almost a yard.
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