
Its primary purpose is as a thermal battery. When it gets real warm in the house (through the solar gain of our south windows), we open up the door to the new room. There is a lot of thermal mass in the walls of the room, so it stores the heat well. There is a large bench across the north wall, which serves as a giant thermal mass.
The North Room is also a barrier between the outside and the interior of the rest of the house. It has made a huge difference in the nocturnal temperature drop in the bedrooms, which stay about 60 degrees when it is 30 outside, with no fire.
Its secondary purpose is as a storage room. We built a table and shelf unit to house my sewing machine, fur operation, fabric, etc. Abe will be putting some of his mushroom and fodder stuff in there. Also tools, boxes, spare mattress will be moved in there shortly, now that it is finished.

The main advantages to Rapidobe are speed and low-cost. The tarp that forms the big bag is a recycled billboard vinyl (cheap or free). We cut many of the posts from our property, and the dirt was right under our feet. It is basically a big bag of compacted earth, which is extremely cost effective for a wall material.

The east wall is styrophone insulation with lathing attached to both sides, stuccoed, like a SIP. It has a metal frame that is welded to the door and to the roof.
The west wall is a temporary plywood and frame wall. We will be adding to that area of the house one day when we do the "west wing", so it just has to block out most of the weather for now. It is tarped on the outside.

All in all, it turned into a really nice room. It is now painted and ready to move into. Guess what we're doing for Christmas?!
For more photos, click here.