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Ranman333 04-01-2013 05:04 PM

Foundation For a Semi-Recessed Storage Shed Under Deck
 
I am in the design/planning process for building a deck on the back of my house. I'm working to finalize a design and will play general contractor by getting the permits, sourcing materials and hiring the sub-contractors (concrete and deck carpentry). The deck will be unique in that I want to incorporate a shed underneath. Currently there is 71" from the grade to the sill of the sliding door on the back of the house (daylight+, but not walkout height)

The idea is to do the following:

Construct a 24' x 14' Freestanding deck based on (6) 6"x6" posts spaced on 10' centers in both directions. (Two rows of 3 posts 10' apart with each post in the row also 10' apart). Beams would be (2) 2 X 12" and joists would be either 2 x 8 or maybe 2 x 10 depending on cantilever. Design would include 2' to 3' cantilever overhangs. "Frame in" around (4) of the 6" X 6" posts creating a 10 x 10' "room". Add exterior sheathing and finish with vinyl siding that matches the house (brick and siding combo on the back). Access gained by a 68"W x 10' paved "ramp" decending to double 32" steel entry doors. Trench drain (with popup 12' away) at base of ramp. Trex Rain Escapes systems overhead to keep things dry.

This is simple enough, but to increase headroom in the shed, my plan is to excavate down and pour a slab and 4 shallow walls (back up to the grade) around 4 of the posts givnig an additional 26" of headroom. Then I would 2x4 frame from the top of the concrete wall to the bottom of the deck joists sheath then vinyl side. If I've done my math correctly, that should give me around 83" - 84" from the floor to the underside of the joists. (just enough to use standard height entry doors). Also, there would be two 2 x 12 beams running along two of the walls.

Where I am confused is on what and how to do the concrete work and set the related 6" x 6" posts. For my area the chart says the post footings need to be 22" dia and in MI 42" deep. That said, the posts closest to the house will need to be at the same depth as the basement footing which will make them around 55" deep. Add 6" concrete walls 9' 6" x 26" high all the way around and it seems like a lot of concrete for footings and a shed. What would be the easiest and most cost effective way to accomplish this in a sound way? Do these walls need to be that thick? Will they require a footing? Could I save concrete costs by using bell footings for the posts (say 12" diameter flaring to 22" approaching the bottom of the post holes)?

Then there's the grade vs. the shed floor (26" below grade). Pour the footings up to the grade and mount the posts on top so there's no soil contact? Pour to 26" below grade and attach the posts with mounts on top but have lumber in direct contact with soil on 2 sides from shed floor to grade? Attach posts with mounts? Bury them in the concrete?

Any words of advice you could give on what is acceptable, required and just how best to do this in general would be very helpful. Thanks to anyone who responds.

stadry 04-01-2013 10:14 PM

that's a big post for even a contractor let alone a wanna-be 1,,, hint: most dwgs require a pro stamp ( arch / pe ),,, quit watching tv & hire a good deck bldr,,, you're probably building a nice frog pond w/that design/bld stuff,,, yes, you'll spend more at 1st however you'll not likely get f'd by some taillight gypsy who'll do shoddy work you accept 'cause you don't know differently :huh: hire the right guy AND you have someone to sue - not just imitate a shrinking violet when your bride points out what's wrong there, there, AND there, too !

certainly would've been a big help knowing where YOUR ' where ' is,,, just sayin',,, some others may wanna advise but there's too much for moi,,, you're welcome !

Ranman333 04-01-2013 11:58 PM

Quote:

Originally Posted by itsreallyconc (Post 1150574)
that's a big post for even a contractor let alone a wanna-be 1,,, hint: most dwgs require a pro stamp ( arch / pe ),,, quit watching tv & hire a good deck bldr,,, you're probably building a nice frog pond w/that design/bld stuff,,, yes, you'll spend more at 1st however you'll not likely get f'd by some taillight gypsy who'll do shoddy work you accept 'cause you don't know differently :huh: hire the right guy AND you have someone to sue - not just imitate a shrinking violet when your bride points out what's wrong there, there, AND there, too !

certainly would've been a big help knowing where YOUR ' where ' is,,, just sayin',,, some others may wanna advise but there's too much for moi,,, you're welcome !


Thanks, I guess...:(

Number one, the only "good deck builder" willing to do this job quoted me $28,000 for this project. My math doesn't come anywhere close to that. I'm thinking $15,000 - $20,000 max. (deck and rails are composite, BTW)


I suppose I was trying to be specific about what I am trying to accomplish so apologies if what I wrote was too much to chew...

I have a competent deck builder, he just doesn't do anything other than standard footings, framig, etc.

My goal is to finalize a plan myself, seek permit approvals, hire an excavation/concrete company to locate and pour the footings, walls and slab, and then contract my deck builder to build the deck.

For location I said I was in MI, but to be more specific Southeast MI (metro Detroit).

While I'm not an architect, I have several years of architectural drafting/drawing experience and I've worked both on a machine shop floor and in the drafting department with AutoCAD. My local muni does not require any "pro stamp" just a reasonable print/set of plans.

GBrackins 04-02-2013 12:30 AM

that's a lot of reading for this late at night, I tried but my vision got blurry ...... maybe I'll take a wack at it come sun up, in the mean time here's something for your reading pleasure. It is the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide." It is based upon the code requirements of the 2009 International Residential Code. I do not know what your code requirements if any are. But it's good advice on how to build a code compliant deck. There have been a lot of new requirements over the past few years because of all the decks that have failed causing injuries and deaths.

Good luck!

Ranman333 04-02-2013 02:57 PM

Quote:

Originally Posted by GBrackins (Post 1150653)
that's a lot of reading for this late at night, I tried but my vision got blurry ...... maybe I'll take a wack at it come sun up, in the mean time here's something for your reading pleasure. It is the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide." It is based upon the code requirements of the 2009 International Residential Code. I do not know what your code requirements if any are. But it's good advice on how to build a code compliant deck. There have been a lot of new requirements over the past few years because of all the decks that have failed causing injuries and deaths.

Good luck!

Thanks. Yes, I have read that guide for building decks and am pretty comfortable with the requirements. That said when it comes to setting the post footings and posts, I see deck builders using several methods.

1) Auger the hole, use a sonotube, fill with concrete to grade and set the post into the concrete. Plumb and square as it dries. Post is encased in concrete. Not easy to replace if rotted.

2) Auger the hole, use a sonotube and pour concrete to the grade. Embed a base connector or drill one in after the fact. Attach post with a post base connector. Post is not encased on concrete or in contact with soil, but may lack lateral strength. Easy to replace one day if needed.

3) Auger the hole. Drop in a pre cast "cookie". set the post on top of the cookie and backfill keeping post plumb abd square. About 30" of the post is in direct contact with the soil. This would be easiest, but I need the post to last. ACQ/MCQ lunber rated for soil? Pitch it in tar? Don't do it?

My only complication to using one of these methods is that I want to pour 6"W X 26"H walls and a slab floor in between 4 of the posts. this means I want the posts to LAST. I have the opportunity to do this right the first time and am loking for some simple advice on what is acceptabe and how best to proceed.

GBrackins 04-02-2013 03:22 PM

couldn't you place your wall so that the posts come down on sit on top of the wall?

sorry taking a short break from work and haven't re-read your original OP

Ranman333 04-02-2013 03:43 PM

Quote:

Originally Posted by GBrackins (Post 1151002)
couldn't you place your wall so that the posts come down on sit on top of the wall?

sorry taking a short break from work and haven't re-read your original OP

I like the way you are thinking, but I think you would still need to lay a spread footing that extends below the frost line and then the wall would be rebar'd on top of that(42" in MI) to uupport the load of the deck overhead..

I'm thinking cylindrical post footings or cast cookies to 42" for the deck load and a monolithic slab with an 8" turndown along the edges inbetween the 4 posts. The 26" walls are essentially retaining walls since the slab is 26" below grade.

Ranman333 04-02-2013 03:55 PM

3 Attachment(s)
Here are a few sketches I made to help better visualize what I want to do. Maybe these will help. Each scetch shos a different way of doing the post footings.

Canarywood1 04-02-2013 05:32 PM

2) Auger the hole, use a sonotube and pour concrete to the grade. Embed a base connector or drill one in after the fact. Attach post with a post base connector. Post is not encased on concrete or in contact with soil, but may lack lateral strength. Easy to replace one day if needed.


That's the method that should be used with a simpson tie,ANY kind of wood should never be in contact with soil or concrete.

stadry 04-02-2013 06:27 PM

might try here - http://www.bigfootsystems.com/?gclid...FQGCnQodP0cACw [ no $$$ interest ],,, there's another on the mkt which incl rebar chairs - saw it @ local home show,,, all the sonotube columns i ever saw sat on conc fnd's - agree no wood in contact w/soil ever as canary sez

Canarywood1 04-02-2013 09:25 PM

Quote:

Originally Posted by itsreallyconc (Post 1151110)
might try here - http://www.bigfootsystems.com/?gclid...FQGCnQodP0cACw [ no $$$ interest ],,, there's another on the mkt which incl rebar chairs - saw it @ local home show,,, all the sonotube columns i ever saw sat on conc fnd's - agree no wood in contact w/soil ever as canary sez


The bell on the bottom of the sonotube is supposed to be the foundation,but not much help if you have to rent a back hoe dig the hole.


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