Pier & Beam Foundation for Tiny Home

[homesteadhappy]

I'm new to the terminology, so please bear with me.

Including the porch on two sides of the house, my total dimensions are 24'x24'. The house itself is 16x20. I am planning on a pier and beam foundation. The county I am in is completely unrestricted (no building codes/zones/permits/building department/etc). There's not a single red light in the whole county and much of the population is Plain (Amish/Mennonite), just to give context.

Frost line is 10-12" and state code says we should have a minimum 12" deep footing for the piers. I was going to go 24" down, 6" compact gravel of some kind, and then 18" Sonotube cement footing. I was planning on doing double 2x8 beams (aka 4x8 beams) and doing 2x8 joists every 16" oc.

I am trying to figure out how many piers I need. I was thinking about doing 4 rows of 4 (16 total distributed evenly), 4 rows of 5, or 5 rows of 5.


Am I wildly off here or is this okay? Thank you! 

[anceow]

As I know, the number of piers you'll need depends on factors like soil type, load-bearing capacity, and the size of the beams. It might be worth consulting with a local engineer or contractor for personalized advice.

[rothbard]

I'm new to the terminology, so please bear with me.

Including the porch on two sides of the house, my total dimensions are 24'x24'. The house itself is 16x20. I am planning on a pier and beam foundation. The county I am in is completely unrestricted (no building codes/zones/permits/building department/etc). There's not a single red light in the whole county and much of the population is Plain (Amish/Mennonite), just to give context.

Frost line is 10-12" and state code says we should have a minimum 12" deep footing for the piers. I was going to go 24" down, 6" compact gravel of some kind, and then 18" Sonotube cement footing. I was planning on doing double 2x8 beams (aka 4x8 beams) and doing 2x8 joists every 16" oc.

I am trying to figure out how many piers I need. I was thinking about doing 4 rows of 4 (16 total distributed evenly), 4 rows of 5, or 5 rows of 5.


Am I wildly off here or is this okay? Thank you!

Piers and beam are engineered foundation, of course you don't have to engineer them but I think it difficult to determine without calculating for your soil.  For 320 square feet 12" frostline you could very easily do a full perimeter block foundation, just saying, then you wouldn't lose any sleep over wondering if it was 100% as you'd be 100% up to IRC prescriptive codes.  I think it took me only 4 weekends to do a foundation 33% larger perimiter than that.  Jus sayin.  Maybe go back and read the debates and decide yourself and you may decide a few extra days of work is cheap insurance if this is your full-time house.

If you decide to keep going with pier and beam maybe you can look around at the amish houses and see and ask what they did?  Might give you ideas of what worked locally.

[MountainDon]

I second the idea for a perimeter foundation. With a 12" frost depth it would be a better than pier foundation and about as much work as a bunch of pier holes, with concrete in the bottoms.  Perimeter would be much more stable than many pier foundations can ever hope to be.

Digging the trench can be assisted with the use of a roto-tiller to loosen up the soil, then shovel it out and rototill some more as necessary.

The more piers you have the more chances you create for uneven settling and movements of the piers.

The AWC calculator can help try different sizes for joists.  A simple cabin without any large loads such as big refrigerators, water beds , etc can likely safely use 30 PSF as a floor load. Floor joist selection will depend upon lumber species and grades as well as spacing, but a 16 foot span is possible for a one floor simple cabin.     https://awc.org/calculators/span-options-calculator-for-wood-joists-and-rafters/

You mention 2 porches. Is that one on a long side and a second on an end?  How do you intend to frame the porch flooring?