Some pole barn construction questions
I am planning on putting up a 36×60 pole barn within the next few months and have seen a few different finished buildings and have some questions. I will be using 6×6 .60 PT posts. Should I put them 3′ in the ground on a 1′ thick footing in a sonotube, backfilling with gravel, or just fill the sonotube to the top with cement and locate the posts on top with a steel bracket? I liked the idea of not putting the posts in the ground but I am not sure if my inspector will let it fly. 8′ between posts or 10′? Any advantage either way? I will be using a doubled 2×12 header across each load bearing 60′ side but want to space the posts 12′ apart on the front 60′ side for door openings. Will I need tripled 2x12s to span the 12′? I have been told the doubled will span 10′ but I dont know about 12′. I will be using manufactured trusses to span the 36′, and will be using steel roofing material over 2×4 purlings. Can I go 4′ OC with the trusses or will I need to stick to 2′ OC even with the lightweight roofing material? This is in NY where we do get a good snowfall once in a while. Thanks,
Dave
Replies
Your local building official is the final answer.
In my portion of southern MI the footing depth is 42+". The bottom 8" is filled with concrete. No sauna tube is typically used unless the top of the concrete is closer than 36" to finish grade. The posts are then backfilled and tamped with a granular or crushed material.
If you were to pour a solid footer up to near grade and place the post on top, you would have to use additional bracing to compensate for the loss of the post's rigidity.
If you are using trusses, you don't need any headers along the gable end walls.
Your truss spacing is designed and specified by your supplier.
Terry
Terry,
thanks for the info. In this case I will need headers, as the door openings will be on the wider load bearing walls and not on the gable ends. Any idea what size built up header I would need to span the 12' post spacing? I will go with the posts in the ground.
TLE gave you some good advice, but I wanted to add a couple of things.
If your posts are 8' OC, I'd put your trusses 8' OC also, so they can set directly on the posts. Typically what I've seen is either 8'OC with 2X4 purlins, or 10' OC with 2X6 purlins. Neither one is better than the other - It's just personal preference.
I've seen some really slick "saddle" purlin hangers that I liked a lot, but can't remember who makes them. Don't think it was Simpson.
When you order the trusses, make sure you specify what spacing you're using. I've been in a building where the trusses were set at 8' OC but only designed for 4' OC. (The trusses were sagging badly, and the guy wanted to know how to fix them) Also, specify whether or not you want the trusses designed for a ceiling load. It doesn't add a lot of cost to smaller trusses such as yours. Can be big bucks for 50 to 60' trusses. I'd specify a ceiling load even if you don't want it - Gives you the option down the road if you change your mind.
As for the headers - I don't think 2X12s would fly for a 12' opening, but it depends on your design loads. I'd suggest ordering an engineered header when you order the trusses. That way you know you're covered.
I agree on the engineered lumber, I have used laminated beams throughout my house and they are a great problem solver. Possibly a solid 5 1/2" x 12" laminted beam? I checked out a pole barn with 13' openings and he had rough cut 6x10 solid beams but I dont know how he got rough cut lumber accepted by the inspector. Also, if I space the trusses 8' apart, are 2x6 purlings really strong enough to span 8' and still support the roof without sagging? Do you put the 2x6s on end rather than flat to do something like that? I suppose if I had the trusses directly on the posts there really would be no need for any headers as the posts would be taking all the load.
MY OPINIONS: from having built more than a few.
Drill 20" holes for the posts(bottom below frost). Drop in a foot of concrete, ,let set up, position posts, brace and fill holes. Set trusses on 24" centers(why get cheap, you can finish the inside ceiling down the road alot easier) Headers from SYP 2x12's will be fine and not sag. Keep your posts at 8' max, space the gable ones out even.
You also get a puff of wind now and again.
A sail like that sitting on top of the ground can really hurt somebody when it goes traveling in a storm.
Anchor those posts aas deep as you can.Excellence is its own reward!
I'm assuming you had a general reply to all and not to me specifically, right? As to the barn sitting on top(as mine have the top of the concrete footing at least 38" in the ground for NE OHIO.)
That's right Keith, I'm still getting the hang of the site and all the options and buttonsExcellence is its own reward!
I was a poultry house superintendant in Arkansas for a few years. I can give you our specs on this at the time.
4x4 treated# 40 posts below frost level 6 inches, or more. We dug a continuous footing. In the footing we dug post holes every 4 ft. trusses on 4 ft center . We also ran two 1/2 inch rebar through every post in the footing continual. 2x4 lath.
WE have lost several houses to snow . Just 1 ft of snow. I dont know however if these houses have ever failed or what the houses that did were built like. But I will say this ; I wouldnt dream of going any lighter than what I mentioned if you have a possibility of 1 ft of snow.
Tim Mooney
As I said earlier, 2X4 purlind are normally used for 8' OC spacing around here. But definitely on edge. You could probably get by with laying them flat up to 4' OC. Whether or not any particular size is adequate for your situation depend on your design loads and the species of lumber you're using.
*And* your local building codes/building inspector.
I can tell you what common practice is around here (NW Oregon).
DO NOT attach the posts to brackets at ground level. In a pole barn, racking resistance to wind load, etc. comes from the poles themselves, and their being embedded in the ground. 0.6 PSF CCA poles do not rot, period. Hole depth will depend on frost depth and how high the walls are, but 4' is used here. Concrete pad at the bottom; alot contractors also use concrete to fill he holes, mostly I think because it's faster than carefully backfilling and tamping another material. Less ideal, but quicker, is not to pour a pad, just place the poles in the holes with alot of spikes embedded in them, and fill with concrete. But I poured pads on the couiple of pole buildings I did.
For 36' span, 6x6 poles 12' O.C. are used. wall girts are 2x6, 2' O.C. Pole barn trusses, designed to be used in pairs (one on each side of the poles), are used, one pair 12' O.C. purlins are then 12' long 2x6 on edge, 2' O.C.
when using the pole barn specific trusses, are they sistered together so that they both sit together on the center of the post? Or are they spaced slightly apart from each other? Are the purlings put on edge on top of the trusses or put flush to the roofline and nailed to the side of the top chord? I havent seen this style of pole barn but it seems very cost effective. I also may be upgrading to 40' deep from the 36', does this change anything as far as post spacings? Also since the purlings are 2x6s on end, does that mean that the top chrord of the pole barn trusses are made with 2x6's or do I have to specify that? Thanks for all the info, this is great. Lots of different ways to build a simple barn!
Edited 3/31/2002 6:41:17 PM ET by drptop70ss
Lots of good ideas so far, here's a few comments from our experience.
Here in upstate NY., we recently put up a new pole barn using .60 6x6 poles set in ground 42" on top of 12" conc. footing. Backfill and tamp with gravel. We went with acantilevered truss design giving us a 10' overhang along one 60' side for outside lumber racks that are under cover. Didn't cost that much more. We went 4' o.c. with 2x6 roof purlins laid flat 2' o.c. and metal roofing. Went with an upgraded metal finish with a longer warranty period. Trusses should be spec'ed by your supplier for the spans and spacing you're planning and if any chance of finished ceilings, for that too as earlier suggested. Our ceilings are metal liner panel screwed up to truss bottoms, no problem spanning the 4' even with insulation above. Plus the ceiling is prefinished white and really brightens up the inside. Our post layout was 8' o.c. maybe overkill but we get alot of wind. One word of caution. Build it about 50% bigger than you think you need because the darn things fill up a lot faster than you plan on.
Ours will someday be woodshop, so I laid radiant heat piping in the concrete floor over 1" of Foam insulation. Eventually I want to hook up a remote location wood/ oil boiler unit, and a backup forced air unit for quick heat.
I'm a little puzzled as to why you would use 2 trusses on just a 36' span. Unless you have a really outrageous snow load, a single truss should be easy to design.
One thing to keep in mind about double pole barn trusses - They may be designed for half the spacing, or may be designed to be nailed together. This affects whether or not you need braces on the webs. Ask your truss manufacturer for more info.
I worked for a company that does about $28,000,000.00 annually ( yes Million! ) building "upper end" pole barns. We had every aspect speced by an engineer who signed off on all loads, wind shear, etc. It is a costly project to gamble guesses. We augered out 24 inch holes four feet deep poured 10 inches of concrete ( let set) Next day dropped in 2x6 pressure treated laminated columns with rebar passing through them ( about 6 " each side) plumbed, braced and poured concrete around them and then backfilled. This seems like overkill unless you consider wind shear and uplift potential. We were never sorry for the extra effort in the foundation. Good luck!
Thanks for all the suggestions and info. I will use the 6x6 posts 4' down on 1' of concrete and then backfilled with concrete. I know some here have posted not to use concrete to backfill, but the building inspector insists on it. I will get a quote on trusses 4' OC but will space the posts 10' except for the one 60' side which will be 12, so I will have an archetect spec me what size laminated beam to span the 12'. Probably going to end up 40' deep also instead of the 36', too much stuff already to jam in this barn! Thanks again.
Glad I could help someone else for a change! Best wishes! If you think of it let me know how it went.
Most pole barns include girts between posts, then vertical metal siding its attached to the girts. I'm thinking if corrugated metal siding were attached horizontally directly to 6x6 posts, there would be no need for girts and the metal would provide lateral shear strength. The only advantage I see for girts is the "ladder" they provide.
Comments please.