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KY Post and Beam Foundations

B

bwky

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Joined
Dec 23, 2020
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3
Location
Kentucky
I'm going to be building a 30' x 30' cabin and was debating what type of foundation to use. It will be a single story cabin, with a slant roof.

I'd like to get the plans approved by the county, so I want to be sure everything is up to code before going through that process.

I'm leaning toward a Pier and Beam foundation due to cost saving aspects, but rarely see these around central KY.

1) Aside from the energy efficiency aspects of having an open floor, any code issues about this? I've skimmed the code and it looks like this type of construction is totally permissible.

2) Foundation would consist of 16 24'' Piers on top of 12' thick, 36'' square footers, 28'' deep in the ground. Pier spacing would be 7'. Girders would be composed of 3 staggered 2x12x12s braced to the piers using the appropriate simpson braces.

I drew it out, but don't see where to attach an image.

Anyway, appreciate any thoughts.

Thanks!
 
Welcome!

If I am understanding your design, I don't know of a Simpson product that would allow staggered lumber seams in a beam. With 7' spacing on the piers, there is no reason that you can't land the seams over a pier.

Design sounds good, worse case, invest a few hundred bucks and get a registered design professional to sign and seal the design.

Good luck! (BTW, if you sign up as a sawhorse, you can attach images)
 
A crawl space might be easier, unless you're on a steep grade. It will give you a space to run pipes & ducts that should stay above freezing, unless the cabin will be left unheated most of the time. If the underside of the floor is left exposed you will need something to protect the insulation from critters trying to burrow in it, such as plywood or hardware cloth plus window screen. A post & beam foundation will also need diagonal bracing.
 
Does a prescriptive post and beam foundation design exist or is that an engineered design? In my world, we would require engineering making the concrete foundation more affordable. I built a house with a plywood foundation 30 years ago. Saved a little money and it still looks good. That was back in the days when your treated plywood had the good stuff, arsenic and copper. I don't think I would try a treated wood foundation with today's treated products.
 
First it is a mortal sin to stagger seams in a beam. They shall always be provided with support of a post. If you go with a crawl space do the following; 1). Provide a 3" thick concrete floor, 2). Insulate exterior walls with 2" foam from top of foundation to 24" below finished exterior grade, and 3). Provide supply and return air on opposite ends of the crawl space. No vents or windows. Treat it like a basement and it will act like a basement.
 
There isn't any design, I'm just drawing up what we'd like.

I had been referring to the following for KY building codes:
Specifically, sections R401 for foundations, R327 for Post and Frame

I did have another question about pier diameter. I'd be using concrete piers, with 6x6 on top to brace to the girders. Section 404.1.9.2 describes a minimum diameter of 12 inches for a pier. I had wanted to go with 18 inch diameter piers, but it sounds like 327.3 requires 24'' for the 30' width of the cabin?

I had planned on stapling foil joist insulation on top and under the floor joists as the research I've done seems to indicate it's better than other options. I debated whether I should put treated plywood under as the bottom, under the foil, but I'm wondering if that'd be overkill.

Regarding the 3 staggered 2x12s for the girders, I was thinking it might be stronger rather than having the beams end at each pier as the entire length would be tied together.

Thanks
 
This is a pic of what I was thinking. I know it's hard to see the staggered 2x's, but they'd all end on the supporting piers. I'd nail the 3 2x's together to form a beam.

Thanks again!
 

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This method is most similar to pole barns except they open span the interior which would eliminate the interior piers and girders. The proposed plan is most common in European construction methods. Call or set up a consultation/meeting, provide your documents and ask questions and requirements. Your building official may or may not require engineering.
 
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