In ,
MJ belched:
In a week, I'll be building a 10x12 shed.

The plans call for a on-grade foundation with 6x6 skids. My property
is sloped. From high pt to low pt is about 8 inches. I called out a
guy and asked about pouring a slab. After I got over the price
objections ($3k), he and I talked about cheaper suggestions. He
said, oh, we could do Sonotube piers. I agreed but the project at
that point stalled as I lost the person who was going to help.

Anyways, I found another person and he said he and I would do the
foundation layout, digging, etc. ourselves. I told him my soil is
kinda hard (clay and possible sandstone). No problem, just water the
area and it will soften. I did a test dig yesterday and the water
didn't drain for over an hour. Hmm, this is gonna be tough going.

Here's where I'm at. I could go with on-grade foundation using solid
concrete blocks to level up the low spots. Not a problem for me, easy
to layout and make happen. Or... we could get a power auger and drill
the Sonotube piers. My helper who is a expert carpenter is away on
vacation until two days before we start, so I can't get his opinion.

Which way would you go? Block or tubes?

My only concern is earth movement. Earthquakes are possibility. But a
rare one. Would one would see a wood foundation come off a cement
block pier in a minor (less then Richter 2) quake? I thought of
drilling into the block and holding the joists with anchors. Can you
drill solid block?

MJ

Personally, i would do the Sonotubes.
I had built a 16x20 and they used concrete blocks. I have to have it jacked
up and leveled every couple of years because the blocks slowly sink into the
ground. I wish now i had done piers/sonotubes
I'm getting ready to jack it up again and I'm going to replace the 4x4 skids
with steel I beams so that I can drill holes in the ends to accomodate a
cleavis hook to hook the farm jacks to and make it easier to jack up with
less stress on the building. Plus the I beams won't warp/twist like the 4x4s
and hopefully stay straighter
jmo & ymmv