Moisture Diffusion

Research done by Tim Padfield in Denmark, shows that moisture absorbing walls play an important role in the health of large public buildings, as well as in private houses. His comprehensive research is worth a visit at

http://www.natmus.dk/cons/tp/phd/phd-indx.htm

Organic Builders who use large amounts of organic materials can rely on those materials to breathe and moderate the moisture variations within the building. "The Healthy House" (1) points to some concerns with modern building design and materials. Air pollution inside a modern building can be many times greater than the air outside. Walls which breathe can exchange and filter the air and greatly reduce internal air pollution. Porous hygroscopic materials such as straw and timber can take in and release moisture and so act as a natural air conditioner. The diffusion resistance factor (DRF) of a material is a useful indicator of its capacity to resist the intake and release of water vapour, and diffusion of stale interior air. Table 5 gives the DRF factors for building materials, the higher the DRF, the less it breathes and the less acceptable it is for a healthy house.

Material DRF
Brick 10
Concrete 35-40
Earth 10
Mud & Straw blocks 2
Straw Bale 2-10
Solid Timber treated with natural paints and oils less than 5
Wall boards - plywood

- chipboard

- tempered, coated hardboard

50-200

50-110

1390

Vapour barriers - aluminium foil

- bitumen

70,000

800-1,200

Table 5 (2)

1. 1."The Health House" by Sydney and Joan Baggs - Harper Collins 1996.

2. 2."The Healthy House" page 134