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Floor joists in an 8x12 coop - Page 2

post #11 of 16

I really want to not have to use middle piers if possible, so I think I will go with the 12' span. Am I understanding you that I need to use 2X8 instead of 2x6 for the joists?  Should these be pressure treated?  I have seen many designs online, and I am hesitant to get started because I want to get it right the first time!  So you would definitely recommend burying the 4x4s down to the frost line? I had seen some folks just put the 4x4's into the pyramid shaped piers that sit on top of the ground.  Is this a bad idea?  I didn't know if it would work doing it that way for such a large structure.

 

I am building a monitor style shed with the center section walls 6' tall, peaking to 8' in the center.  The outer sections will be 4' tall at the outside to save on 2x4s, and join the center section at about 5'.

post #12 of 16

With the structure off the ground the only thing that should be pressure treated is the posts. I would put the posts below frost line in your area otherwise your building with rack up and down each spring. Most soils wont hold that large a structure on little cement post stands- they will continue to settle. By burying the posts or setting into buried concrete piers you have both surface area bearing on soil and friction along the side of pier. It's not going anywhere doing that and it's such a small amount of work to dig down X amount (don't know your area) of feet to prevent frost lift. When all is said and done with this building you'll have a fair amount of time and money into it. A day of labor more and little money for 8"sonotubes and 6 bags of concrete isn't much at all. Being an outbuilding it's not so imperative to get down below deepest frost ever but a good amount down. Like here in the North a footing should be 5' down, I'm happy going 3ft on a small outbuilding and only 2ft on privacy fence posts.

 

And if your building is really only going to be 4' high on 16' ends then you don't need the 6 posts. Go with 2x12's to make the beams and four posts (one each corner) then get the sonotube deep.

 

To shave some money and wieght you can frame all the walls in 2x3's 2ft on center. Once sheathed with plywood it's a truss and will hold enormous loads.


Edited by Egghead_Jr - 11/5/15 at 1:10pm

Everybody talks about the weather, but nobody does anything about it.

 

-Charles Dudley Warner

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Everybody talks about the weather, but nobody does anything about it.

 

-Charles Dudley Warner

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post #13 of 16

Thanks for all the good advice!  I am in Tennessee, and for plumbing, they use 18" to get below the frost line.  

 

I think I misled about the height.  It will be 4" high on the 12' ends.  The monitor is on the long (16') ends, so it will go from 4'-5', and then the monitor section will go from 6'=8' peak.  Does that make sense?

 

Our Lowe's lists the non-treated 2x8x12 as Top Choice #2 Prime Kiln-Dried Southern Yellow Pine S4S Dimensional Lumber (Common: 2 x 8 x 12; Actual: 1.5-in x 7.25-in x 12-ft)'  It is listed as "#2"...is that OK?  Also, they have 2x8x16 for about $13 each.  Are you saying I should use a doubled 2x10 beam or a single 2x12 beam, or should it be doubled no matter what?

 

Thanks again!

post #14 of 16
Quote:
Originally Posted by Egghead_Jr View Post
 

 Yes, the piers can be pressure treated 4x4's right out of the ground from frost depth or use 8" sonotubes and put bag cement in, devolop around the 4x4's last 12" of sonotube.

..and sorry to be such a noob, but what does this mean exactly?  Especially the "develop around the 4x4's" part?

post #15 of 16
Quote:
Originally Posted by screasy View Post
 

Thanks for all the good advice!  I am in Tennessee, and for plumbing, they use 18" to get below the frost line.  

 

I think I misled about the height.  It will be 4" high on the 12' ends.  The monitor is on the long (16') ends, so it will go from 4'-5', and then the monitor section will go from 6'=8' peak.  Does that make sense?

 

Our Lowe's lists the non-treated 2x8x12 as Top Choice #2 Prime Kiln-Dried Southern Yellow Pine S4S Dimensional Lumber (Common: 2 x 8 x 12; Actual: 1.5-in x 7.25-in x 12-ft)'  It is listed as "#2"...is that OK?  Also, they have 2x8x16 for about $13 each.  Are you saying I should use a doubled 2x10 beam or a single 2x12 beam, or should it be doubled no matter what?

 

Thanks again!

In my opinion, for an outbuilding, number 2 lumber is fine for the joists. It means that knots are allowed in the board, and some edges may be "live" meaning exposed bark. If you're selective when picking through the pile, you can minimize both. Make sure to observe the "crown" of each board (all boards will have a bit of an arch to them, called the crown) and set them crown up. 

 

For a 16' span, doubled up 2x12's is what he's recommending and will be more than sufficient. If it's me, I also buy a sheet of 1/2" plywood to sandwich between them, if only so that the final thickness matches the width of the 4x4 post you'll be setting them on. Basically you cut the 4'x8' sheet of plywood into strips 11.25" wide x 8 feet long, and sandwich it between the 2x12's using liquid nails and screws or framing nails to hold it all together.

 

As for the question about "develop around the 4x4's" for the posts. You only need the sonotube form where the concrete extends above the ground - the hole works as the form below ground. I believe that is what he's saying - for the 12" above ground, use sonotube to maintain the pier's shape. 

 

If frost depth in your area is 18", dig the holes for your piers to at least 20" to be safe. Personally I'd go 24" since it isn't that much more concrete and you only get to do this once. Keep the hole diameter between 8" and 10" and make sure there's no loose dirt in the bottom. For good measure, you flare the bottom out to 12" diameter or so to spread out the weight - especially since we've cut it down to 4 piers. Now, this might add confusion, and it is certainly a debatable subject, but my opinion is this: Don't set the 4x4 posts in the concrete piers. Eventually, water will soak in to them, and even though they're treated, they will soften up and rot away. It will take awhile but it will happen. Instead, use anchors set into the concrete, then fasten adjustable post bases to the anchors, and lag your 4x4's into those.

 

Egghead_jr, feel free to disagree, but an even more simple way to do this is to not use 4x4 posts at all. Bring the concrete piers to 12" or 16" above grade (depending on your final height decision) using the sonotubes, with anchors set in the centers. Then fasten on adjustable post bases, and those can be wrapped directly around the doubled 2x12 rim joists (especially if you sandwich the plywood in there, as I recommended). This avoids "stilts" holding up your structure. 

 

Here's an example of the adjustable post base I'm talking about: adjustable post base. I don't see that Lowe's carries anything adjustable like that, but Home Depot does. 

And the anchors you'll want to set into the wet concrete: anchors

 

Hope this helps!

post #16 of 16

Egghead_jr, thanks for info. :thumbsup

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