Uplift on 12x28 Lean-To

[jaw22w]

I am adding a 12 x 28 lean-to on the south gable end of my 30 x 40 pole barn. The 28 feet length will be open to the South. The 12' side walls will be sheeted in. I am starting to worry about the uplift potential this presents. I drilled the holes in the ground for the poles this past weekend and will be standing poles in the holes this coming weekend. I am using 4x6 treated poles. I am thinking about purchasing some 1/2" rebar and drilling the poles horizontally for a 12-16" piece of rebar. One rebar close to the bottom of the pole and one about 2 feet up and 90 degrees from each other.
The rafters are attached to the pole barn at the 12' level with Simpson rafter hangers at the high end and screwed to the poles at the low end at a 3/12 slope.
The site has a wide open field to the South and does receive a lot of wind, hence my worry about uplift.

Is my rebar method acceptable? Or necessary? Is there another method for countering uplift in a situation like this?

Thanks for any insight

 

[jack stand]

I have read post frame trade magazines suggesting this exact thing.

Is my rebar method acceptable? Or necessary? Is there another method for countering uplift in a situation like this?

 

[manwithtools]

How deep are the holes, how deep will the poles be set, what is the diameter of the holes, will they be filled with concrete? All of these variables will impact your situation.

 

[gsmith22]

How deep are the holes, how deep will the poles be set, what is the diameter of the holes, will they be filled with concrete? All of these variables will impact your situation.

all of this. make holes bigger, run rebar through posts and fill holes with concrete creating large boat anchors. without running numbers too difficult to say how much here or there but make it stout never fails

 

[jaw22w]

How deep are the holes, how deep will the poles be set, what is the diameter of the holes, will they be filled with concrete? All of these variables will impact your situation.

The holes are 16" diameter x 52" deep with 6" of concrete in the bottom. So the 4x6 poles will be embedded 46". I had planned on just dirt backfill. I thought putting concrete around the poles leads to rotting the poles out, but that would definitely help hold 'er down.
A thought occurred to me that I could install one of those mobile home hold down screws next to each of 4 poles into the ground. That should at least keep the structure in place.

 

[Firebrick43]

The holes are 16" diameter x 52" deep with 6" of concrete in the bottom. So the 4x6 poles will be embedded 46". I had planned on just dirt backfill. I thought putting concrete around the poles leads to rotting the poles out, but that would definitely help hold 'er down.
A thought occurred to me that I could install one of those mobile home hold down screws next to each of 4 poles into the ground. That should at least keep the structure in place.

They put uplift anchors in around here when the set poles for pole barns.

The ones common here are two pieces of galvanized angle approx 2"x2"x8" bolted thru the post with a 3/8 or 1/2" bolt.

The second method if using wet concrete instead of a cookie is a galvanized stirup that is approx 4" wide and goes down the 6" depth of the concrete, over the width of the post and back up to the post. The top two edges are bolted again with a thru bolt on the post. 6" of concrete is poured in the hole and the stirrup not only locks the post to the footer but also keeps it from sinking into the footer and later rotting due to it.

 

[gsmith22]

The holes are 16" diameter x 52" deep with 6" of concrete in the bottom. So the 4x6 poles will be embedded 46". I had planned on just dirt backfill. I thought putting concrete around the poles leads to rotting the poles out, but that would definitely help hold 'er down.
A thought occurred to me that I could install one of those mobile home hold down screws next to each of 4 poles into the ground. That should at least keep the structure in place.

yes, generally you don't want the wood in the ground and certainly encasing in concrete doesn't help with rot. helical piles can be both your foundation (for uplift and downward load) and keep the pile out of the ground. certainly would be a better way to construct but I was trying to stay within your original parameters. see RR Buildings on youtube for example

 

[Firebrick43]

yes, generally you don't want the wood in the ground and certainly encasing in concrete doesn't help with rot. helical piles can be both your foundation (for uplift and downward load) and keep the pile out of the ground. certainly would be a better way to construct but I was trying to stay within your original parameters. see RR Buildings on youtube for example

How would you attach the poles to the helical piers to take the bending moment, the very thing that defines a pole barn?

 

[gsmith22]

you wouldn't. it would have to become a post frame which is why I didn't initially suggest it - "trying to stay within our original parameters"

 

[Hank11]

Can you let some air escape to mitigate lift? If the air had a place to go it might help a lot.

 

[gsmith22]

do not under any circiumstance open doors during a wind event to "let air escape". what you are doing is changing the building from "enclosed" to some variation of "open" allowing pressurized air to enter and push up on the underside of the roof from below. It would certainly increase the interior pressure; building codes estimate as much as 3x. to limit uplift, you want your building enclosed menaing as few holes on the exterior envelope as possible.

 

[Kpaige]

As said helical piers would be the for sure no issue solution. You will get no heaving, no sinking, and no lifting.

 

[racecougar]

I expect that Hank11 was referring to the lean to rather than the building proper.

OP, what are you running for a header at the poles? What pole spacing are you utilizing?

 

[jaw22w]

I checked into the tie down screws. $10 each at Tractor Supply. That's some pretty cheap insurance. Might help save everything but the tin.

Thanks guys. It always helps me to talk about a problem like this.

 

[jaw22w]

I expect that Hank11 was referring to the lean to rather than the building proper.

OP, what are you running for a header at the poles? What pole spacing are you utilizing?

The header is 2x10 on the inside and outside face of the poles. Spacing on the poles is 8'-6.5" on each end with 10'-11" in the center.
The spacing is odd because when laying out rafter hangers @4' o.c. the layout had to be adjusted to miss the vertical sheeting ribs because the header at the barn is installed under the truss and under the siding.

 

[Firebrick43]

As said helical piers would be the for sure no issue solution. You will get no heaving, no sinking, and no lifting.

The issue with helical piers is you can’t use the poles for bending moments that pole barns are designed for.

This is what takes all the wind load in a pole structure.

Then you have to design a pretty significant structure in an open lean to to have all the wind loads be converted into strictly shear load to be transferred to the helical piers.

Further more there is no issue with poles heaving if they are below the frost depth, sinking if the are setting on a cookie or footer, or up lift if the correct brackets or stirrups are used.

While helical piers are a solution for foundations in poor soil conditions for more standard platform or ballon framed construction, they have no place in pole building and is just a very expensive solution for a non existent problem in pole buildings.

 

[Hank11]

I expect that Hank11 was referring to the lean to rather than the building proper.

OP, what are you running for a header at the poles? What pole spacing are you utilizing?

Right.
If this shed roof didn't have closed ends we wouldn't be writing about this.