Civil Engineering Reference
In-Depth Information
Figure 14.2: The McLaren Leisure Centre, Callander: a healthy building materials specification,
with dynamic insulation in the ceiling. Source: Howard Liddell
The thermal insulation property for static insulation is usually called lambda
(
) and can be measured with special equipment:
= W/(m°k)
Mineral wool has a lambda value of 0.04, while a woodwool slab has a value of
about 0.08. This means that a double thickness piece of woodwool gives the same
insulation value as a single thickness of mineral wool.
Calculating the value of insulation
The example quoted above comparing the thermal insulation of two materials is the
traditional method of calculation, making the assumption that there is a linear rela-
tionship between the lambda value and insulation/heat loss. There are limitations to
the lambda values. They give no indication of the material's structure, moisture prop-
erties or reaction to draughts (which every wall has to a certain extent). It takes no
notice of the material's thermal capacity. In buildings that are permanently heated, as
