What are the advantages of living in a straw-hut? Well it shields you from the warm rain and if you can tolerate the heat in the summer, the humidity and general lethargic atmosphere with a little breeze then this is the perfect sustainable environment with little initial investment. It is getting more difficult and less fun if you are trying to work in such an environment.
For all other environments where the air needs to be chilled or heated in the most cost-effective and environmentally sustainable manner using some form of climate control, air conditioning and insulation are the only options. Modern buildings will use the most effective insulation techniques and materials, highly efficient lighting systems that generate the highest light output for the least watts possible, and lower energy heat pumps in air conditioning systems that rely on highly effective insulation.
The insulation material between your outer fabric and your sheet-rock (UK: Plaster Board) wall is what matters.
The three materials I like most are Self expanding foam, open cell or closed cell, Styrofoam and Neoprene. Styrofoam is blown into a cavity and then expanded using steam. It can fill any cavity and produce a very effective heat and cold insulation. An Aerogel is by far the most effective but has to be produced in sheets or blocks and cut to size for the application and therefore only practical in new construction while Styrofoam can often be applied to an existing cavity.
The most effective material available today is called an Aerogel, this is not a brand but the type of material which has extreme durability and heat insulation properties within the likely operating temperatures in any environment on planet Earth. There are water-repellent varieties of the material which are best for regions where high humidity and dampness are main features of the local climate.
Both materials require experience and are not recommended to apply in a do-it-yourself way. There are specialized companies in almost any country that will apply those materials.
Most commonly used in North America is self-expanding foam from two component epoxy. However, self-expanding open cell foams are not as efficient mainly due to the poor consistency and often poor preparation of surfaces and poor application, they will also degrade much faster than the Styrofoam or the Aerogel which will generally out-live the building. Closed cell foam is the most durable, has almost twice the insulation performance compared to open cell foam and adds to the structural capability of a building but it is also three times as expensive.
A very good material for insulation in all climates might be open cell Neoprene the material that is also used to make wet suits. In 1/8 of an inch or 1/4 of an inch thickness the insulation capabilities outperform foam insulation in heat conductivity as well as long-term durability in cold and wet climates. The material comes at around the same price as expanding two component foams, it is less of a mess to apply but may need more skill as it only comes in sheets or rolls.
All three materials are sustainable as they will either degrade or remain a non-toxic filler. However, all three materials are produced in toxic and volatile processes. In my view the benefits of the materials outweighs the dangers resulting from the manufacturing process as the process can be controlled so it has less of an environmental impact.
Any “Green” Architect will have their own experiences and views as to what materials are best to use in your application as the material you are trying to stick the insulating material to may have different requirements. Wood for example takes expanded closed or open cell foam very well while the underside of a metal roof needs to be meticulously clean, if not the material may peel off or provide pockets for water to collect in.
So if you are building a new structure or renovating an old one to become a state-of-the-art “Sustainable Living or Working Environment”, it will require the most energy-efficient lighting to create the least amount of heat, an air conditioning system that is pumping heat in or out of the space most efficiently and most effective insulation to not introduce or lose heat or cold through wall, ceiling or floors.