Pier spacing ... who/what is correct?

[hnash53]

I've been reading about pier spacing...sometimes for houses/cabins I've read 5 ft, 6ft, and 8 ft.  I'm assuming using 6x6 posts.

Also, I've seen some plans for 20'-wide buildings that use two beams with cantilever, and sometimes three beams with or without cantilever.

I'm looking at doing a 20' wide with 1 1/2 stories.

Whazzup?

Confused in Wyoming.

[John Raabe]

There are lots of different ways to build a successful post and pier foundation. For any particular design larger beams can carry the weight to fewer piers with wider footings or better bearing soil. Or you can have more piers and a smaller beam. A bit of a cantilever on beam or joist is a free ride on the stiffness of the structural member (did I really say that?   )

Best advice - pick a foundation plan that has the same loading (floors and roof) as the building you are doing. If you extend the building don't exceed the spacing between piers or you will have to resize the beams - drop in an extra pier or two if needed.

If you end up building in sub standard soil (clay or silt) then add an extra pier or fill a wider hole with crushed rock to support the load better. Most foundations are designed for 2000 psf of soil bearing. Good sandy gravel soil can be 3500-4000 or higher.

The third beam in some designs is likely because of smaller joists and an internal bearing wall. I like to use engineered joists for 20' spans (supported at either end). You can also use 2x8 joists and span them 10' to an interior bearing wall and foundation beam.

You can see that the foundation plan is draw up last after the structure of the house above it is designed.