I've been making foundations like this and others for over 20 years. I don't find it is necessary to get the harder to find blue board, the pink board works fine - it has more than enough compressive strength.
Good drainage is critical. Rubble, gravel, drain pipes, slope on compaction or ledge all work. Our foundation looks somewhat like the one on the right except we poured it all as one thing, not in multiple pours for footer and slab. The layers go:
Interior of cottage
Floor slab of steel reinforced concrete
Gravel with drain pipes embedded
The edge of the foundation is shaped to thicken it to be a beam downward and upward to be kneewall on the south and west. All one mono-pour. We used block in other area for walls. There are a few small contact points between the beams of the foundation edge and the ledge to give firm support. This makes it so the house is not actually resting its weight on the insulation.
is about 100,000 lbs of concrete, masonry, stone and brick completely within an insulating envelope on a 252 sq-ft foundation. It has a few anchor points to the ledge of the mountain, keying in around natural protrusions so we won't slide down the slope. It stays warm very easily, takes a minimum (3/4 cord) to heat and collects passive solar energy that soaks into the thermal mass.
Eventually we'll berm around the house and over the barrel vault concrete (ferro-cement) roof. A project for another year. That will further improve the thermal performance and lift the wind up off us more.
One of the beauties of the cottage is it is plumb, straight and level. Previously I've been fixing up old houses. A level surface is wonderful!
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project: