Out Building / Pole Building questions

[NLazyA - Addy]

I have followed so much of these threads and have really come to appreciate the advice and knowledge of all you guys. I would appreciate any experience or advice you guys might have here. I have built only one pole barn in my life.

My friend who just bought property next to us (that is a good thing) is building a 48x50 pole outbuilding. He had it designed and plans to frame it like the pole buildings here in this forum and use metal for cladding and roofing. His designer sez he doesn't need to put any OSB or other support before putting on metal siding or roofing. It seems that if you don't use that, the metal siding could oil can, or get older faster due to wind, or something. ALso, how would you place a waterproof membrane on the roof?

My second question is backfilling the poles. the ground is a very mixed sandy/clay mixture. The designer also had him put a base of concrete in the holes (he is using 6x6 posts) first and then backfill the posts with concrete. When i built my first one, i just filled and compacted each pole with native material and didn't seem to have any problem.

Does anybody have any thoughts?

Thanks.

Jim Noetzelman

 

[MarkV]

Jim, for a metal roofed pole barn it is pretty standard not to use sheathing like OSB under the metal. Generally trusses are set at a spacing appropriate for your area, snow load, and then purlins are set perpendicular to the trusses for the metal to be screwed to. Properly installed metal roofing does not require any type of water proof membrane.

Different folks have different thoughts on backfilling the posts. Some like to use concrete the way your the plans call for while others feel that traps water between the concrete and the post causing rot. Some like to use native soil or stone dust as back fill to promote drainage around the post. A 16” round concrete donut or base for the post to sit on is pretty standard in my area.

MarkV

 

[EddieWalker]

His designer sez he doesn't need to put any OSB or other support before putting on metal siding or roofing. It seems that if you don't use that, the metal siding could oil can, or get older faster due to wind, or something. ALso, how would you place a waterproof membrane on the roof?

My second question is backfilling the poles. the ground is a very mixed sandy/clay mixture. The designer also had him put a base of concrete in the holes (he is using 6x6 posts) first and then backfill the posts with concrete.

Jim,

On filling the holes with the posts, it's pretty common to due just about any combination that you mentioned. Local Code changes so drastically across the country this that I don't think there is a proven "right" way to do it. From what I've learned, it seems that just about every way works.

The only real concern is to get the water away from the area of the pole that is just above the ground. This is where they rot and have all their problems. Have really good drainage and keep the pole dry and the rest is taken care of.

For the metal roof, it's standard to attach the metal to the purlins. If he is going to insulate, then depending on what he is going to use, certain types of insulation go between the metal and the purlins.

The problem with using decking and metal roofing is moisture. Metal roofs condensate water and will rot out the decking if it's not water proofed. If OSB, plywood or any other type of decking is used with metal roofs, then felt paper has to be used to water proof the decking. I don't know why anybody would add the addition expense of decking a metal roof, but it is done on existing homes with decking and that's whre the felt paper is used.

Eddie

 

[WVBill]

The manufacturers' web sites provide literature that says if/when and how you should use decking under their metal. Here are a couple of links:

Fabral

American Building Components: Metal Roofing, Metal Siding and Metal Building Construction

I put metal roofing on both my pole barn and the stick-framed studio I built for my wife. The pole barn is uninsulated, sided with T1-11 and unfinished on the inside and the studio is fully insulated, drywalled and sided with vinyl siding. Both have trusses with horizontal purlins as Mark V described.

Just to be sure - per the manufacturers directions - I used rubber sealant at the overlaps of the panels on the studio building.


WVBill

 

[NLazyA - Addy]

Eddie, Bill, Mark,

Thanks so much for your help and the information. Eddie/Bill, i appreciate the common sense on the addition of a wood deck before putting on a metal roof ( i have always appreciated all your posts on this forum!!). I think i don't "trust" the rigidity of the metal roof alone, and i need to rethink that now. It makes sense not to put in something that you don't need!!

When i have put in fence posts in the past, i have noticed how concrete seems to shrink and there is always a small gap between the post and the concrete...and that seems to fill with water.

I'm going to share this info with my friend. We hope to start the building early July.

Thanks guys.

 

[WVBill]

I think i don't "trust" the rigidity of the metal roof alone, and i need to rethink that now. It makes sense not to put in something that you don't need!!

Jim - the "rigidity" of your metal roof will come from two things:

One is the bracing you will add to your trusses. The horizontal purlins help some but you will need to have diagonal bracing also. Your trusses should come with truss design drawings and a copy of the BCSI booklet on truss bracing. Go here WTCA - Representing the Structural Building Components Industry for more info.

Second is that your purlins will probably be 2-feet OC so your metal panel is only spanning about 1' 8-1/2" unsupported. I've been up there in a bucket lift when I was putting it up - it's darn strong.

Best of luck. I was putting the metal roof on my studio building last August - believe me, that metal gets "HOT!"

WVBill