Organic insulation materials may not have as high an R value per inch as polystyrene and fireglass, but when they are used in sufficient quantity, they can provide sufficient insulation. You need to consider the other advantages of organic materials, in that they breathe, they absorb and give off moisture, they are non-toxic, they take very little energy to process, they can be easily recycled, and they store carbon.
The following table compares the insulation value and energy requirements of a range of building materials. The 2 columns on the right are the important ones for the Organic Builder. The right hand column shows the thickness of material needed to provide R11 insulation. The second column from the right shows how much energy would be required to make a square foot of that material of the required thickness. Concrete and masonry brick are very poor insulators. The organic materials, softwood air-dried, flax, lambswool, corkboard, sawdust and earth, all require considerably less energy to provide the equivalent insulation of fibreglass, or polystyrene.
Insulation value and energy requirements of building materials
||Density lb/cu ft
||R Value per inch
||Energy Btu/cu ft
||Energy for R11 sq ft
|Flax Fibre Panels
|Softwood - Low Energy
Source - Mainly from "Living Spaces - Ecological Building and Design" - OKOTEST
The Organic materials shown in green, can easily match the insulation value of fibreglass and polystyrene by using thicker walls. However, the organic materials require much less energy than fibreglass and polystyrene.
R 11 ( or R1.5 in the metric scale) is about the minimum required for walls in many countries. If Organic Builders have access to abundant supplies organic materials such as straw, flax fibre, dry sawdust, timber, logs and earth, then it makes sense to make walls much thicker than minimum standards. This can be done for little financial, or energy cost. This will give greater comfort, and reduce energy running costs, and help the building achieve a high sustainability index.