Shallow pressure treated foundation

[TheWire]

I'm looking at building a 20x32' 1.5 story cabin in NE Wisconsin.  The site has about 6-8" of sandy top soil with clean dry sand and large rocks at times under that.  As the area is on top a slight hill, I expect it will always be fairly well drained.  I'm looking at my foundation options.  I'm thinking about going with a shallow system as the site is not easily accessed by large equipment and the acreage has a lot of granite boulders which could hamper attempts at digging piers.

The system I first looked at was a series of 2x2x1' holes filled with gravel and tamped.  Adjustable concrete piers would be set atop the gravel.  I was looking at going with these piers at 4' intervals along the outside walls and down the center support.  Here is the place I found this: http://www.coyotecottage.com/cabin/cabinconstruction/foundation.htm

I have looked at pressure treated foundations in the past for a house I built and this idea occured to me.  Its basically setting a PT Wood foundation on grade on top of gravel.  Here is my thought process:

Dig a trench 1' deep and 2' wide matching the perimeter of the cabin ensuring the trench bottoms are undisturbed soil/sand.

Fill this trench with washed 3/4" limestone gravel, level and compact.

Build two  32'x2' and two 20'x2'walls out of pressure treated (PT) wood.  Glue and nail pressured treated 1/2" plywood to 1 or both sides.  This box beam would give these walls strength to deal with slight variations in support by the gravel.

Nail a 2x8 PT footer to the bottom of these walls and set them on the gravel.  

Set a center beam and support it with short piers on 2x2x1' gravel holes.

Set the floor joists across the walls & the center beam and put occasional angle braces between the bottom of the 2' walls and joists to provide tip over resistance.

I was also planning on placing 2' wide band of foam insulation on the ground around the outside and backfilling slightly.  The foam would disrupt frost action, which I would not expect a lot of anyway, and protect the trenches from getting hit with rain water.

I would probably add some large screw in anchors for wind resistance.

I would appreciate any comments on this foundation method.

Thank you,

Jerry

[jraabe]

You have described the crawlspace version of the All Weather Wood Foundation.

Here's an overview. http://www.toolbase.org/Technology-Inventory/Foundations/wood-foundations

I have plans for this and a wood framed basement foundation as an option in the 2-story Universal Cottage plans.
You can find much more history and information on a search of "all weather wood foundation"