Building insulation materials weak and brittle. Before its risks were recognized, it was used because it was a cheap, effective insulator with a high R-value and its open-cell structure was a good acoustic insulator. Though it absorbed moisture easily, it regained effectiveness as an insulator when dried. Asbestos once found common use as an insulation material in homes and buildings because it is fireproof, a good thermal and electrical insulator, and resistant to chemical attack and wear. It has been found that asbestos can cause cancer when in friable form (that is, when likely to release fibers into the air - when broken,
Dynamic insulation medium (m) is known. The air permeability of some materials that could be used in dynamically insulated walls or ceiling are listed in Table 3. Air permeability data is crucial to the selection of the correct material for the air control layer. Further sources of air permeability data include ASHRAE and Kumaran. Table 3: Measured Air Permeability of Building Materials (1) Pressure drop calculated at flow rate of 1 m/mh The application of the theory of dynamic insulation is best explained by way of an example. Assume a house of 100 m floor area with a dynamically insulated ceiling. Putting