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bobbotron
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# Posted: 5 Jun 2014 22:15
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So we're planning a deck for this summer, I wanted to get some input and feedback with my design.
So the cabin is on the top of a large hill overlooking a lake. It's built on a large flat area, nice sandy soil for the most part. About 8' away from the edge of the cabin, the ground starts to slope down. We want to build an 18'x18' deck, half of it quite close to the ground, that extends out down the hill. It'll be about 8' in the air at the far point. We'd like to have it as close to ground as possible near the cabin, as it works well with the rest of the layout of the area, and it will mean we wont get snow build up against the doors on that side of the cabin. The cabin is about 2' up on that side.
So we were planning on doing three beams to support the deck, and making it a free standing deck, it wont be the same level as the cabin's structure, so there's nothing to lag a ledger to (* see below!)
The plan is for each beam to have three piers, each pier 8" sonotubes with 14" footings. Each beam will be 3x10s. Joists will be 2x8" PT. The first two sonotubes will be basically on the same grade as the cabin, the last one will be down the hill. I plan on adding braces from these down the hill posts, to the beam and to each other.
The beams will be perpendicular to the side of the building.
* So my dad was up the other week, helping me mark out the end perimeter of the deck. He was suggesting that instead of putting a row of sonotubes near the cabin, we could lag bolt a ledger board to the cabin sonotubes, and use heavy duty joist hangers to attach the deck beams to this ledger. I've never seem this suggested on the internet, but I thought I'd ask you guys what thought of this. I'm not sure I dig the idea. I could see possibly pouring deck sonotubes AND lagging a header to the cabin sonotubes for extra strength. Anyway, I'm quite interested to hear what's thought of this.
** He also mentioned instead of putting joists on top of the beams, we could install hangers between the beams, so the deck surface would be 7.5" lower - this would make for a slightly better view from the cabin which is definitely desirable. 
I've attached a rough sketch of what I'm talking of. Interested to hear what people have to say. I've run this structure by my building inspector, who is great, but I quite appreciate to hear what others have to say. I've not run * or ** by him yet.
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Jim in NB
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# Posted: 6 Jun 2014 08:19
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Nice big deck! - a wide! The front deck on my camp is 32x12 - fits the front of the place! I too had a really good slope to deal with. I attached it to the camp and then constructed five pads (2x2' x 8" with rebar) with 6x6 posts, the one beam was triple lam 2x10s with joists 2x8 16"O/C. I used 4/4x6" decking, all wood was PT. Extra PT ledger board on camp joist and then joists attached with hangers. My beam runs parallel to the main building obviously. The deck has held up amazingly well. I have a metal roof which discharges half it's snow load right on to the deck - some pretty wild build ups of ice/snow which I usually go down and shouvel off mid winter. I am very happy with the results after five winters. The only thing I would do differently is triple lam 2x6s rather than use 6x6s for the posts. Easier to haul and construct and permits the ability to better integrate the braces into the structure.
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toyota_mdt_tech
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# Posted: 6 Jun 2014 08:50
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The lumber sizes, spans etc are plenty. I know with 2X8 joist you can go closer to 12 feet long at 16" OC. At 8 feet long, should be nice and solid (no bounce)
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bobbotron
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# Posted: 6 Jun 2014 10:25
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Thanks toyota. I thought so too, I seem to be getting in the habit of over building things. I considered using 2 2x10s for the beams, instead of 3, but 3 seems to be proper overkill.
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Don_P
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# Posted: 6 Jun 2014 23:12
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awc's deck construction guide is commonly accepted or referenced by many building dept's.
http://www.awc.org/codes/dcaindex.php
One thing you'll notice is that max girder span is 8'. This allows a built up girder of 16' or shorter lumber to be alternately spliced over the piers helping to weave the girder into a continuous beam.
Jim in NB raises a good point, snow load can be the controlling load in some areas rather than occupancy load. I've seen decks sheared off of buildings by sliding snow from the roof dropping onto the deck.
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bobbotron
Member
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# Posted: 9 Jun 2014 16:32
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Thanks for the feedback guys!
So we dug some holes this weekend, decided to do 4 per beam on the outer two beams, currently 3 on the middle, 4 still be in the cards. Got 6 out of 11 dug to 4 feet, lot of work.
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Jim in NB
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# Posted: 26 Apr 2016 06:19
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Was going thru some old posts and thought I would add another comment to this post and something to consider if you have big snow loads and a metal roof. In 2015 we had fairly big snow loads with no melts - the snow went all at once. The pictures tell the story - the snow took the railing off. Was a pretty easy reattachment. I have since taken out spindle sections of the railing system to let the snow pass thru. There was no damage to the deck flooring or supporting structure. If you have snow load - best to set up the discharge away from your deck!
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NorthRick
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# Posted: 26 Apr 2016 16:22
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Was anybody home when that happened? If so, it must have scared the living daylight out of them! I know when our little cabin sheds snow off the roof it can be startling for sure.
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Jim in NB
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# Posted: 27 Apr 2016 07:41
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No unfortunately I wasn't there - would have loved to have been over to the side taking a video though!
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