Planning a deck, a bit confused about spans, footing sizes

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Small Cabin Forum / Cabin Construction / Planning a deck, a bit confused about spans, footing sizes


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bobbotron Member	# Posted: 16 Jul 2013 06:59pm Reply So I'm looking to build an 18x18 foot detached deck in Southern Quebec, nearish to Ottawa (fair snow load in the winter.) It's starting on top of a hill, will be about half on a hill, half drops down to a second shelf about 5 to 6 feet down. I'm thinking it'll have three beams, running perpendicular to the hill. Each beam will have either three or four posts, making for a span of either 9' or 6', with one or two posts on the top of the hill, and one or two down the hill, each at least 4' deep. The deck will be very close to the ground on the top of the hill - basically the beam will rest right on the sonotube. I'm planning on using 6x6 PT posts, and 8" sonotubes. 2x8 ground rated PT for the deck joists and probably two ground rated PT 2x10's for each beam. I plan on putting the outer beams about 6"'s in for the side of the deck. I'm somewhat confused about what size of footing I'd need - I've looked at a few span tables and each points to a different size. My dad didn't even use sonotubes for his raised deck at his cabin, but I think I don't want to do that here. I plan on putting a lot of bracing on the lower posts as they will be a ways up in the air, but not nearly as much as some decks near my place. So I'm thinking either no footings or a 14" footing for each tube. Maybe bigfoot footings, but wow they require a big hole. I have no idea what kind of decking I'll use yet, maybe some kind of 4/3" cedar decking. What do you think? Suggestions? Something I'm not thinking of WRT to building on a hill? I need to run all of this by the inspector, but I like to have these things lined up first.

optimistic Member	# Posted: 16 Jul 2013 07:59pm Reply Did you look into http://www.technometalpost.com/en/home/? From what I calculated it is almost the same price as doing sono tubes with cement and big foor but a whole lot easier. They give you a reading, signed by their engineer, as to how much load you can put on it. Unless you go to an engineer - it is hard to get exact figures on what kind of wood/beam load to run. That's why I always do an over-kill.... I will do triple beam from 2x10's with bolts and construction glue. Then use this calculator for the joists : http://www.awc.org/calculators/span/calc/timbercalcstyle.asp You would play with how much 'in' to put the beam to make the joists and over-kill - reducing span.

knock Member	# Posted: 16 Jul 2013 09:52pm Reply bobbotron - a lot will depend on the inspector and what they require. Submit what you want to do and they will likely make the necessary corrections. I am sure they handle things like this all the time. Here is a deck guide from a city down here in Missouri. On one page they set out pier sizes based upon the square footage of deck being supported. (Drawing on page 3 and table on page 4) Pier size can also be affected by soil conditions. http://www.marylandheights.com/Modules/ShowDocument.aspx?documentid=5199 I would go larger than an 8" sonotube (just my 2 cents), but I tend to overbuild. Good luck

bobbotron Member	# Posted: 18 Jul 2013 05:11pm Reply I haven't looked into metal posts seriously, not heard a lot of good things about them locally, as far as price goes. Maybe I'll phone around! Quoting: optimistic Did you look into http://www.technometalpost.com/en/home/? From what I calculated it is almost the same price as doing sono tubes with cement and big foor but a whole lot easier. They give you a reading, signed by their engineer, as to how much load you can put on it. Unless you go to an engineer - it is hard to get exact figures on what kind of wood/beam load to run. That's why I always do an over-kill.... I will do triple beam from 2x10's with bolts and construction glue. Then use this calculator for the joists : http://www.awc.org/calculators/span/calc/timbercalcstyle.asp You would play with how much 'in' to put the beam to make the joists and over-kill - reducing span.