Pole Barn design ideas for hurricane alley

[George_W]

Hello all! I'm brand new here and have been reading some of the very helpful post here. I thought I'd try and solicit some advice from some of the knowledgable people here!

I'm planning a 28wx40lx14 to 16'h pole barn (pilings on 8' centers) on the east coast (close to the beach) that has to be rated to withstand 130mph winds. In talking with the local contractors and building inspector they specified 8x8 pilings with 8' embedment in the ground (sand). Thats about all they specified other than it having to meet the 130mph wind code. There is all sorts of stuff in the code for stick framing and conventional footing/foundation walls but nothing on pole framing. Ironically everyone that I've spoken to- county inspectors, piling contractors and building contractors, highly recommended the pole barn over conventional stick framing for its superior wind/racking resistance and overall strength. Other than paying a professional engineer for a design and stamp I'm kinda at a loss on several key design specification elements.

My submitted plan specified 2x6 horizontal girts on 2' centers with 7/16osb and 8" hardiplank horizontal lap siding-blind nailed.

Several things concern me now that I've started checking into it further. First-the James Hardie Website (http://www.hardie.com/pdf/ner-405.pdf) shows that Hardiplank nailed over OSB isn't rated near where I need it to be in wind resistance. Nailing it directly to 2x4 conventional framing (vertical frame) at 16" o.c. meets the parameters but now throws my girt plan in the trash. I'm certain this has to do with nail strength in 7/16th inch osb versus pullout strength of all nails going directily into framing. Actually now that I'm thinking about it the osb isnt really necessary...its used in conventional stick framing for racking/sheer resistance as much as just a nailing surface. With the non-load bearing walls as found in pole construction it wouldnt really be necessary.

Anyway, building a 16" o.c. 2x4 stick frame between pilings will burn up twice the wood, more cuts, more time and also the question of how to fasten it securely to the timbers and floor. Not to mention finding long straight 16'-2x4's to run vertically between pilings and how to fasten conventional framing securely between piles. If I use foundation bolts in the slab...I now have to turn it down on the edges and it takes away from the idea of "free floating walls" that the girts would provide. Then there is the additional expense of the concrete. I'm sure that in using conventional verticle framing I'd be losing some strength the girts would have provided in tieing all of the pilings together too?

The are other possible options for me but I'm not thrilled with them. My most recent idea would be using hardie panel (basically 4'x8' cement fiber sheets) similar in concept to plywood horizontally over the girts. They are designed to to be nailed vertically with the long edge supported by framing...however horizontal layout over girts would accomplish the same thing I think? I'm thinking that using these sheets with such high side walls would really make it look like an awkward slab sided structure without the breakup horizontal lap siding would provide?

With lack of code specs on this I'm sure I could get away with my original design, however I want to do the right thing and not have my little barn explode during the wave of hurricanes next year.

Anyone have any suggestions?

Regards,
George

 

[chucko]

one thing to think about on a open building is uplift. The shape od a roof is almost like a wing and you can get a lot of uplift. A lot more than pole in just sand can handle. Have the truss company run you some trusses for a open building at 130 mph wind in a costal zone. The drawings will have reactions on them both gravity and wind (uplift)....Then just start adding numbers up to be sure you connections can handle it

 

[SPIKER]

sounds like you have some thinking , lanning and drawing to do.

I'm not sure how to go about it with you set up either. like chucko said talk to all the local lumber companiest that would be providing price quotes to you. get as much info on what OTHERS have done in you're area and go from there. I would think that steel framming would be you're best bet in a commercial type building. not as pretty but you can get the high walls you want with less hassle & be more wind friendly...

MarkM /forums/images/graemlins/crazy.gif /forums/images/graemlins/confused.gif

 

[George_W]

Thanks for the suggestions guys. I know I'm in a special situation but still wondering if anyone out there has installed hardipanel by itself on 2x6 horizontal girts...no sheathing underneath? I've seen T1-11 done that way. Just trying to avoid the vertical framing if I can.

Chucko, its interesting what you said about the embedment in sand. It seemed counterintuitive to me utill it was explained.

Anyway down in my area 90% of construction is done on pilings...beyond keeping things out of the flood waters the water table is so high...poured footings arent the best foundation.

When you go down 2' or so you hit a wet sand slurry type mixture...its rather like quick sand. They only auger the holes down 2-3' or so and insert the piling. They then use a water pump (basically a 3" trash pump necked down to 1" on a long pvc pipe. They stick this down next to the piling and it washes/floats it right on down 8 feet. Once they're down they are set by hand with a large sledge hammer a final 1/2" or so and they are locked in. They aint coming straight up by any kind of pulling unless and until you break the hydraulic lock thats put on them from the wet sand. Iive tried to get old 4x4 posts out myself and they broke off (they werent rotten either) when I put the jack and truck to them.

A local builder told me that each 8'x8' pile has a bearing potential of around 20 thousand pounds + each. I know its hard to believe but all of of the reading I've done supports this. Evidently the bearing strength comes from the friction on the side of the pile not the base as one would expect in terra firma. I dont know what the uplift rating is but its got to be huge also.

 

[chucko]

I understand what you are saying but if the building gives you x# of uplift than you will need and eng or the building department to sign off that the poles in the sand can handle that much.

There are lots of new wind codes out now that were not in place before. Some things are no longer allowed even thouh the house beside you is buit the same way you want to and it mad it through Hugo

 

[texbaylea]

I was doing research on building with SIPs which are OSB faced. I found that Hardie Plank recommends double nailing 8" o.c.. This means face nailing at the exposed edge through the under plank. I will try to find again the link that had this information.

Vernon

 

[Cdash]

I know that 8 feet deep sounds like a lot and will never get pulled out, but one thing that happened this hurrican season that took out quite a few piling supported buildings was storm surge scour. If your on the beach, near the beach or in the path of the storm surge, you can easily loose 4' of soil, leaving you with only amounts. Although if you loose that much soil, you may be a total loss anyway.....

 

[MarkV]

George,

I believe HardiPlank makes a vertical siding for a board and batten look. Wouldn’t that solve your nailing problem? No idea on wind load for it.

MarkV

 

[George_W]

Cdash,
You are right on about that!! I saw some devastation last year that I didnt think possible from exactly that...scour and the pushing/lifting power of the water. A couple of hotels were literally ripped from their poured footings and pushed across a highway. Another one was undermined anc collapsed on itself from SCOUR. It is amazing the digging power that fast moving water exerts on things. Four or five piling houses near the beach were lifted off their pilings by the tidal surge actually more of a tidal wave. Two were carried away a mile into the sound. I think their surface mass and open bottom encountering fast moving/rising water were more than they could bear. The pilings held in most every case though...the ties/bolts/banding/joists etc. being the weakest link, just let loose.

While I am not exactly on high ground, I'm not close to the water. I'm in an area of thin woods in the shadow of sand dunes-some as high as 60'. I do get a little rising water on my lot during direct hits but fortunately its not moving with any velocity...it just slowly rises. Its costing me a fortune but I'm filling the whole lot 2' to get 1' above the base flood (100year flood) line.

Chucko-I see what your saying. I probably should have explained a little better. I think the problem I'm having is the total lack of code for ground level pole buildings. I'm not using trusses or rafters...it will be 8x8 timber all the way to the peak with roof purlins across the timber. The only pertinent code i've found there is for pilings in general... 8' embedment, 8' o.c. max on the load bearing side, 12' max on all other sides. All the rest of the code is pertaining to stick built "load bearing shear wall" structures. Since the pilings themselves are the load bearing portion, the walls between them are floating with the piles...not bearing in any way. I have a permit for the building in hand...I just want to make sure I'm building the walls strong enough for ground zero. I'm pretty confident the timber/piling portion of the structure will be sound, its the walls and more specifically the siding that concerns me!!! Even though the building department approved it without requiring any engineering...I am second guessing my 2x6 girt board/osb/hardiplank walls. I also dont want to keep making inquiries to the BI and bringing something he may have overlooked in the plans to his attention.

 

[OkeeDon]

Someone else mentioned truss design. Here in Florida, that's a lot more important for windload than the siding you choose. The HardiePlank may not have enough wind resistance to hold up in 130 MPH winds, but it's not going to affect wind load. For wind load, what will be much more important is keeping your poles in the ground, keeping your top beam attached to the poles, and keeping your trusses attached to the top beam. Next, will be keeping your roof attached to the purlins and the OSB sheathing attached to the girts. In other words, if you do lose some of the HardiePlank because the nails didn't hold, your damage would be cosmetic, not structural. The only real danger is that your lap siding would add to the flying missles during the storm, and there will be plenty of that regardless of your siding.

While James Hardie Company says it's OK to install HardiePlank on vertical studs 16" on center with no backing, I'd personally not do it. I have some fairly extensive experience with both HardiePlank and HardiePanel, and the stuff, while wonderful, is fairly brittle and can break easily if hit sharply with no backing -- like if you bumped it with a front end loader. Metal might dent in the same circumstances, but probably wouldn't leave you with a big hole that would be dificult to repair! I plan on using HardiePlank on both my house and barn, but it will be on SIPS (with OCSB) on the house, and OSB cladding on the barn. I'll nail using the normal nailing pattern and not worry about wind loss on the siding.

I have currently have a small commercial building (about 1200 SF) with HardiePlank nailed directly to old, slightly rotten T111. I lost no planks during hurricane Frances, but lost one board during hurricane Jeanne 3 weeks later. I'm convinced it was only because of the double hit. We were directly in the center of both hurricanes, about 10 miles from the coast.

I think your best bet would be to go ahead with the OSB cheathing and HardiePlank like your original plans. If you are really concerned, go ahead and place a visible nail in the bottom of each plank every once in a while, maybe 16" to 24" OC, or even further. All you're trying to do is prevent the wind from getting a finger-hold on the bottom of the plank and starting to peel it up.

{EDIT} I was writing this while you were composing your previous message about not using trusses. Still, my advice in the first paragraph still holds, just that it will be making your that your roof beams stay attached will be one of the critical areas. Frankly, the 2x6 girts almost sound overbuilt. If your nailing them flat to the poles, through the 1-1/2" side, I'm not sure how much more strength you'll gain with a 2x6 over a 2x4, or even whether you'd need that extra strength once the OSB is attached.

Also, I wanted to add that the HardiePlank will give you the cleanest look to the siding, because any of the other solutions -- such as the HardiePanels or any vertical siding that is less than 14' in length (or however high you go) wll have some sort of joint that will be unsightly and require trim. For example, using the 4x8 sheets horizonally as you mentioned would require horizontal battens every 4' and vertical battens every 8' to cover the joints -- it would look like a checkerboard.

If you're really concerned with the holding power of the nails in the OSB, you'll have to consider using plywood for the sheathing.

I think the lack of design standards for the siding is just because they don't care about that, as long as you have the structure correct.