Shed roof uplift and ground anchoring concern
Hi. I am in Zone 4a near Nashville
I am concerned about winds turning my shed roof into an airplane wing. What would be the advice on keeping the roof on and posts in ground?
KEY ELEMENTS:
18x56ft shed roof, no walls (except high side – barn)
12-16ft off ground
Only 3 6×6 posts 28ft O.C.
Details:
Enclosed Gable Pole Barn:
16′ walls.
28’x56′ enclosed
Shed roof.
18×56 ft shed roof
No sides
3ea 6×6 posts supporting the 56′ of roof at 28ft O.C. spacing of the posts.
Girders – bar joist girders
2×10 rafters 24″O.C.
2×4 purlins
metal roof. No sides.
The high (barn) side of the shed roof will be about 16ft high and the low (eve) side of the shed roof will be about 12or 13ft high.
Occasional high wind gusts.
Shed roof faces south and prevailing winds come from south/southwest.
Note: I need the spacing so I have plenty of room for logs, sawmill, lumber; so, more posts are not an option I am considering.
Am I wrong to be concerned?
Thank you for your advice.
-Mike
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Replies
You can use steel straps looped around the top the bar joist and nailed into each side of each joist as a type of hurricane tie to prevent the rafters from lifting off the bar joist.
The bar joist to post connection is probably already fastened to the posts with bolts or some other type of connection that won’t lift.
If those posts are set in concrete or are sufficiently deep they probably won’t lift (this is “check with an engineer territory). If you’re trying to retrofit some uplift protection, screw-in earth anchors such as those used to guy utility poles can provide thousands of pounds of pullout resistance and can be installed slightly out from the posts and then connected with steel cable or chain with a bit of tension to help hold things down.
Chances are occasional wind gusts aren’t a huge problem unless you get BIG gusts. The steel strap ties is cheap insurance though and might be all that’s needed, but if you’re really worried get the posts checked out, use earth anchors, or put some concrete piers in as anchor points.
Bill