Currently, Approved Document E (1992 edition) gives guidance on suitable building materials using generic names, densities and physical dimensions. There are a number of problems with this. First, there is less of an incentive for manufacturers to develop new materials not included in the generic descriptions. Second, the generic descriptions do not make it easy to calculate the mass-spring resonance frequencies of walls and floors in the same way that thermal conductivity enables the calculation of U-values.
For example, for a concrete floor slab with a 65mm floating screed, Approved Document E currently contains guidance on the use of 25mm mineral fibre quilt with a density of 36kg/m 3, or 5mm closed cell polyethylene foam, as the resilient layer.Measurement of these materials' dynamic stiffness conducted at BRE's Acoustic Centre has shown that the mass-spring resonances of such floors are approximately 50Hz with a glass fibre quilt and approximately 150Hz with polyethylene foam. Therefore, knowledge of the resilient layers' dynamic stiffnesses means that it can be known, prior to specification, that with glass fibre, improvements in impact sound insulation begin at a frequency about 100Hz lower than with polyethylene foam.