Frost Protected Shallow Foundation

I've been spending many man-hours working on the plan. We spoke with a concrete contractor regarding the footers, and he had some interesting facts to share with us. The first fact was the two foot [24 inch] frost depth required for footers here. I had been thinking about the amount of concrete we'd need to adequately support those big posts, and had settled on 12 inch depth, 36 inch square footers, but to avoid using excess concrete, we were planning on laying each footer on a bed of ruble 12 inches thick. The local code, however, requires a depth of 24 inches for a footer. No matter, we can accommodate that. But I recalled something I had come across before regarding shallow foundations, and frost protection I'd like to share.

A frost-protected shallow foundation system was started in Scandinavia. They use rigid foam insulation set around the outside of the foundation to protect against frost heave. Such shallow foundations reduce costs several ways. First, you have less excavation and backfill. You can use significantly less concrete by not needing to pour footings below the frost line. Since we plan to use in-floor radiant hydronic heating,
it just makes sense to combine the insulation of the surrounding foundation with the slab insulation.

SketchUp revised versions

 

Image via Wikipedia

 I have been getting more confident with SketchUp. I can't say enough about this program. As you can see, We plan an upper floor. Stairs are yet to be inserted. The loft doors on each end will be flanked by windows. I need to frame up supports for a bale lift, a beam extending out from above to hang a block and tackle from, above each end door. I also plan to put a pass-through from above each stall. And then comes the roof! The question is: trusses versus site-framed rafters, in the post and beam style.

 

The bottom view shows some features of the foundation. Each of the twenty upright posts will need a firm footer. I have planned for three foot square footers, 24 inches deep. The county building inspector will no doubt have a significant say here! My plan is to dig a trench for the outer perimeter footing, that will support the bale walls. It will be 24 inches deep, and 24 inches wide. The outer wall posts will set on the inner edge of this perimeter footing, with a bump-out three foot long and 20 inches wide, so a full footer will support each of those posts. I will ask the county inspector about rubble trench technology. We may be able to decrease the amount of concrete yardage by using compacted rock in the trenches. * Finally, the foundation will be insulated with EPS [expanded polystyrene] boards, and protected from rising damp with a good vapor barrier.