Dr. Owen Geiger and I have collaborated on a new article posted at earthbagbuilding.com
that describes how to use earthbags filled with various natural insulating materials to insulate ceilings or roofs.
There seems to be a general lack of interesting ceiling options using sustainable building materials. For instance, when touring otherwise beautiful straw bale homes one often sees sheetrock covering conventional industrial insulation. Instead of using fiberglass batts or even manufactured cotton batts to insulate a roof, it is possible to use earthbags that are filled with a variety of insulating materials. These materials include rice hulls, crushed volcanic rock (such as scoria), vermiculite and perlite.
The insulating value of these ranges from about R-2 to R-3, so they are quite effective, and can also be quite inexpensive to install.
This article also describes how one might use mats made of natural fibers to cover and finish these earthbag ceilings.
Suspended ceilings, as described in this article, have a number of benefits. They conceal the roof structure, plumbing, venting and electrical wiring, as well as improve acoustics and insulation. And they can also greatly enhance the ambiance or hominess of a room.