Pole barns and footing loads?


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Old 11-24-14, 08:30 AM
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Pole barns and footing loads?

I am looking to build a 16' x 24' pole barn in my backyard to function as storage for equipment as well as a place to work on my vehicle out of elements. I am on a 1/4 acre lot, so space is at a premium. I'm also subject to lot coverage restrictions, so I can't/don't want to build anything with a larger footprint. For storage of things like seasonal decorations, out of season clothes, etc...I'd like to go up and incorporate two large (10' x 16') lofts at either end of the building. Essentially what I would do is build the pole barn and then balloon frame the loft platforms at either end with the poles carrying the weight of the loft and material stored in it. What I'm wondering is how I can be sure that I won't be overloading the footings of the poles?

My building inspector has signed off of on the plans and told me to assume a soil bearing capacity of 1500lbs/psf. The NRCS classifies soil for this area as "gravelly loam." Basically its soil with bits of clay and crushed up granite mixed in. I am planning on 24" diameter footings, which will have a bearing surface of 3.1 sq/ft, so 3.1 x 1500 = 4650 x 12 footings = 55,800lbs. How can I be sure that my footings will support the weight of the building, any snow load (I'm in NJ), and the contents of the lofts? I have run across resources on the internet that will give weights of various building materials-everything from dimensional lumber to sheathing to roofing, so I could add up the weights of everything on the materials list and start there?
 
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Old 11-24-14, 09:50 AM
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I'm surprised the inspector signed off without this detail already answered. Drawings usually include all the below grade support/foundation for the building specified above. If these are engineered drawings, I would head back to the source and ask for that detail.

Bud
 
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Old 11-24-14, 09:56 AM
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How can I be sure that my footings will support the weight of the building, any snow load (I'm in NJ), and the contents of the lofts?
You could add up the weight, but I think you'd be wasting your time. You need an engineer to figure the load calculations. Normally when plans are submitted, the city needs to see the structural calculations. It's more complicated than just figuring the weight of what's above and dividing it among available bearing points. It involves how the weight is distributed (transferred down), footing depth, and so forth.

The weight of items placed on loft has no bearing here, there will be an assumed live load and dead load. However be sure when submitting plans, you make it clear the lofts will be part of design.
 
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Old 11-24-14, 09:58 AM
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I'm surprised the inspector signed off without this detail already answered. Drawings usually include all the below grade support/foundation for the building specified above. If these are engineered drawings, I would head back to the source and ask for that detail.
These are not engineered drawings but rather a design I came up with myself. Since this is a storage building not meant for habitation and not connected to my main residence, the requirements do not seem to be that stringent. Basically he looked over my drawings and told me that the bottom of my footings had to be 48" deep to meet frost depth requirements and didn't get more specific than that. I live in a small town and the inspector is an older guy. When I showed him the drawings he said "Mmmhmm...just basic construction-looks good." This is what he approved:

[ATTACH=CONFIG]42332[/ATTACH]
 
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Old 11-24-14, 10:27 AM
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As you did the design yourself, you cannot blame anyone else.

What you plan on putting up in the "storage" areas is only what you plan to do now. This always increases and grows. There is no way you can get a reasonable "design" by picking and choosing materials stored. What if you decided to "temporarily" support some other materials or toys, like snow mobiles and the hurrican Sandy hit?

What you are doing is idealistic (arbitrarily selected loads, connections and weather conditions) and would not be looked at favorably by a buyer in the future. What happens if there is a wind storm after a wet snow when you just doubly loaded the posts and footings. - The slab provides no support vertically or horizontally in most conditions.

The building official allowed you to use use your assumed soil bearing capacity (for vertical loads), since you are the responsible "designer". That does not address the soil types, moisture conditions, water table and lateral strength.

Once it was called a "pole barn" you are put in that slot, which is the worst that can be built for the proposed purpose and materials. I worked for a company that had well built "pole barns" for outdoor storage and never ended up being really stable thanks, but survived thanks to the rigid roof truss system (horizontal diagonal bracing) that could work with poles that were not plumb after a few years.

Dick
 
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Old 11-24-14, 10:51 AM
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Points well taken. I need a 16' x 24' building with loft storage that I am going to do all of the work myself on, and I have a budget of $5000. What should I do? I will say this though-I have no plans to store anything like equipment or "toys" up in the loft for a number of reasons-there's more than enough room on the ground floor for what I have/plan to have, I'd have no way of getting it up there anyway. We're talking about Christmas decorations and rubbermaid tubs full of clothes, camping gear, hunting and fishing stuff, etc... As far as resale value I don't really care-I'll be leaving my current home in a pine box
 
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Old 11-24-14, 11:26 AM
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Let's back up for a second since you haven't got this half built, like many do before they ask, but your cost vs size doesn't seen workable. Not criticizing, just doing a reality check.

Will you be having a dirt or gravel floor? Or pouring a slab. With dirt or gravel it is hard to seal the inside from the outside. If you are planning on pouring a slab, maybe that is where you should be starting. A couple of years ago I helped a relative put up a traditional 2 car garage and he, with a tiny bit of help from me, did all the labor and struggled to keep the cost under $25 a sq ft. Now, yours will probably not be as finished as his was, but materials have gone up considerable since then and your $5K is going to be stretched mighty thin.

Bud
 
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Old 11-24-14, 11:32 AM
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I can't give you "official" advice....

The "Old Guy" Inspector has probably seen many of these buildings in your area and "knows" it's acceptable, or will stand up for awhile.

I would suggest that when planning lofts: Place posts under outside ends of rim joists or outside ends of beams, post will run down and have a footing under each post.

Consider trusses for roof, this will add to cost though.
Attach roof members to top plates with hurricane ties (seismic ties).

At each corner of building, install 4' min. shear panels, total of eight.
If a wide opening at front, install minimum 2'-8" shear panels at opening sides.

Consider drywall on inside walls. 5/8" drywall does provide additional shear value and qualifies as an interior shear wall.

There are other Moderators here, Chandler and XSleeper, who are very good at this, so hang in for better info. Oops, and Bud...
 
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Old 11-24-14, 11:42 AM
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The plan was to keep it simple at first and then improve it over time. I ruled out a slab early on because of cost. The floor will be compacted stone dust. Think of this as an overgrown garden shed-very simple. It's a place to keep the tractor, log splitter, snowblower, lawn mower, chainsaws, generator, etc...out of the rain and give me a place to wrench on my vehicles out of the rain and to store out of season stuff. No electric (yet). I have a 12' x 24' attached garage right now but that is getting converted to bedrooms to accommodate a growing family, hence the need for the pole barn.

My biggest gripe about the attached garage was that though it was big enough to hold all of my stuff, everything was packed in and if you wanted to get one thing out you had to move ten other things. I don't really need a place to store MORE stuff, just a place to store my stuff with enough space to walk around it, move things, etc... Over time the plan would be to add electric, insulation, some kind of heat source, and probably a 10-12' wide lean-to, but right now the plan is literally just to build four walls and a roof to keep out the rain.

Consider drywall on inside walls. 5/8" drywall does provide additional shear value and qualifies as an interior shear wall.
Good advice-I was actually going to do one better and use 1/2" OSB. I have access to a lot of it that was used for temporary structures for free. It has lots of screw holes, but that won't matter for my purposes. I will also be removing some from my current attached garage as I had applied it over the sheetrocked walls so that I could hang things easily.

*EDIT*
One last note-I was quoted $3800.00 in materials from my local lumberyard (they beat Lowes by about $400 and I'd rather give them the business anyway). The only thing that does not include is the stone dust and rental fees for a mini Bobcat to level the site and the auger attachment for post holes. I'm definitely going to run over $5000, especially with the beer and pizza I'll need to feed my "workers" (dad, father-in-law, neighbors), but not by too much hopefully.
 

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Old 11-24-14, 09:10 PM
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While I understand wanting to do things on the cheap, I have to ask--why wouldn't you put the electrical (service panel, runs, lighting and receptacles), and insulation, in place before installing wall sheeting? You're making a lot of unnecessary work for yourself, adding it all later. Or will you be content to run extension cords from the house when you want to work out there after dark? And work in the cold?

From an engineering perspective, I think your design is flawed. You will be building, in effect, a 22' tall sail, which is unlikely to withstand even moderate wind loads common to your area. Without a properly-engineered roof and walls, racking and collapse are likely, and your homeowners insurance will be reluctant to fork over thousands of dollars to replace the building and all of your stored equipment, without having an EOR (engineer-of-record) to go after. You might consider contacting your insurance agent before renting the Bobcat, telling them what you plan to do, and how much coverage you want on the structure and contents.
 
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Old 11-25-14, 06:31 PM
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You might consider contacting your insurance agent before renting the Bobcat, telling them what you plan to do, and how much coverage you want on the structure and contents.
You might be surprised at the answer to this-I know I was. I called my insurance company directly (no agent) and they told me that my homeowner's policy has coverage of $26,500 for accessory structures on the property which includes garages, barns, sheds, etc... I asked if they needed to see stamped drawings or anything like that and they told me that as long as the proper permits are pulled and the local code official signs off that it's fine with them. I suppose that because NJ is such a highly regulated state in general they assume that no one is going to get away with building something shoddy. Come to think of it though, they told me the same thing about my wood furnace installation-all I needed to do was pull the proper permits and have a satisfactory inspection. Other people with other insurance companies have had to provide drawings, take pictures, have an inspector hired by the insurance company come out, etc...

However, I've decided to take a different approach to this and looked at the possibility of stick framing a building instead, but with a foundation not unlike a pole building. I had read this article a while back and gave it another read today:

UMass Amherst: Building and Construction Technology » Wooden Grade Beams

Basically the idea is to pour piers, bolt a beam to the top of them to form a perimeter, and use that as the foundation/sill for the building. The building sits on individual footings as a pole building would, but it can be stick framed by virtue of the wood sill around the perimeter. I threw this drawing together quickly, but you get the idea. It's basically a copy of kit built sheds for sale all over the internet like this one:

Best Barns Richmond 16x24 Wood Storage Shed Kit

This company lists their 2x6 truss (it's not really a truss) with plywood gussets as rated for 90 mph wind load and 30lb psf snow load. I would think that mine would rate a little better since I plan to use 3/4" plywood and make the gussets quite a bit larger. They also only gusset them on one side. I could also upgrade to 2x8s for not much more money:

[ATTACH=CONFIG]42395[/ATTACH]

As you can see I'm still planning on balloon framing the loft in order to make more headroom up top, but I would think this would add rigidity to the walls? Curious to hear others thoughts on this.
 
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