Sustainable Building Glossary

Specific heat capacity: Indicates the heat quantity in joule [J], which 1 kg of a substance absorbs or discharges if its temperature is increased or decreased by 1 Kelvin [K]. For some building materials arithmetic values of the specific heat capacity are listed in BS EN 12524 or test values have been established by the manufacturer. The higher the figure the better does a product protect from summer over heating (among other)

Suction: Depending on their suction and hygroscopicity some materials absorb and desorb vapour quickly and others relatively slowly. Materials that adjust their moisture content minutely are not hygroscopic for the practicality of buildings.

Surface Condensation: The surface humidity is dependent on the interior temperature and room humidity. It occurs when warm moist air meets cold surfaces, on cooling the relative humidity in the moist air reaches 100 % and liquid water forms. Surface condensation is common around windows and doors where reveals are not insulated, hardly any airflow occurs and where there is thermal bridging that goes right through the building structure in insulated buildings. It is also common on the whole of walls, windows and roofs of uninsulated buildings when internal warmth and moisture are present. Surface condensation is also possible on the outside of buildings where there is thermal bridging (for example through uninsulated fixings through EWI systems) and in many other situations.

S-value: Formerly called S_d-value it is the vapour diffusion-equivalent air layer thickness. It is related to vapour resistance and is calculated by multiplying the μ of the different materials with their thickness [m]. The result reveals the vapour permeability of a build-up (wall, roof etc.). The lower the s-value, the more vapour-open the build-up. As an example wood fibre insulation board 0.10 m x 5 (μ) results in s = 0.5 m and XPS-rigid foam insulation board 0.10 m x 150 (μ) results in s = 15.0 m.