Vapour diffusion | The resistance of a building part to water vapour diffusion. |
|---|---|
Vapour diffusionresistance | The resistance of a building part to water vapour diffusion. (This can be understood as the pressure difference in Pa acting for 1 second on 1 m2 to drive 1 kg or water vapour through the building part). |
Vapour barrier | Foil, and similar materials, capable of reducing water vapour diffusion through a structure. |
Vapour pressure | The partial pressure exerted by water vapour in an air mixture (Pa). |
Drainage mats | Sheets of insulation material which (when fitted to exterior basement walls) ensure that water is conveyed directly down to the perimeter drain. The insulation material must not possess capillary properties. |
Dew point | Dew point or dew point temperature is the temperature where RH is 100 % (when air cools). |
Dry well | The subterranean collection point for rainwater from buildings without outlets. Can be filled with pebbles or made of special elements. Water is removed from the dry well by slow percolation. |
Geotextile fabric | A non-woven textile fabric made exclusively from synthetic materials which will not rot. Geotextile fabric is used as protection against gravel or soil infiltration (e.g., in drainage and roof constructions). |
Moisture barrier | Layer of material preventing capillary action (such as foil). These barriers protect moisture-sensitive materials against construction-related moisture. |
Foundation wall plates | Thin profiled plastic sheets which (when fitted to exterior basement walls) ensure that water is conveyed to the perimeter drain. |
Hydrophobic | Water-repellent. |
Hygroscopic | A material is said to be hygroscopic when it sorbs moisture from its surroundings. |
Thermal insulance factor | This factor describes a material layer’s resistance to thermal conduction. If the thickness of the material is d and the thermal conductivity is λ, its insulance factor is expressed as R = d/λ and it has the unit K∙m2/W. |
Insulation property | See Lambda value (λ-value). |
Capillary suction | Moisture transport from pore to pore in porous materials without the exertion of water pressure. |
Weather screen | The outer surface of a building (i.e., roof, exterior walls, windows, doors, ground floor slabs, crawl spaces, basement floors and walls). |
Condensation | Occurs when humid air is cooled to below dew point temperature. |
Convection | Moisture transport where water vapour accompanies airflows. |
Thermal bridge | A thermal bridge is an area where the insulation properties are less effective than in the surrounding construction. Thermal bridges may result from the insulation layer being penetrated by a material with greater thermal conductivity. Thermal bridges may also result from faulty insulation (such as insulation not being fitted tightly around the surrounding structures). |
Bulking | The swelling of a material as a result of wetting it. |
Lambda value/λ-value | Lambda values indicate thermal conductivity and are expressed by the Greek letter lambda (λ). Lambda values indicate the amount of heat, measured in W h, conducted through 1 m2 of a material with a thickness of 1 m during 1 hour when the temperature difference between the surfaces of the material is 1 °C. The smaller the λ-value of the material, the better its insulation properties. |
PAM-value | The former designation for vapour diffusion resistance of material layer (with the unit mmHg h m2/g). |
RH | Relative humidity percentage. Thus, 50 % RH indicates that the air contains half of the water vapour it could potentially contain at a constant temperature. |
‘Tent effect’ | The phenomenon by which wetted watertight materials (e.g., old-style tent cloth) lose their impermeability when touched from the underside. |
Z-value | Vapour diffusion resistance for material layers (SI unit: GPa s m2/kg). The vapour diffusion resistance of a material layer indicates its water vapour permeability. |