Protection from Weather
Cladding of the rear-ventilated facade offers protection from weathering to the load-bearing structure, the water-repellent thermal insulation of facades and the substructure. The protection of rear-ventilated curtain-wall facades from driving rain is characterised by a high level of reliability.
The physical processes involved here rule out capillary water transport and any direct exposure of the heat-insulating layers to rain. In addition, moisture can always be dispersed via the ventilated space. This allows damp insulating layers to dry out quickly without any harm to the thermal insulation.
The free ventilation cavity between the façade cladding and the layer behind it must be at least 3/4". Tolerances and plumbness of the building must be taken into account. In some places, this rear-ventilation space may be reduced locally up to 1/4" – e.g. by means of the substructure or the unevenness of the walls. The rear-ventilation space requires intake and exhaust vent openings. The openings with a cross section of min. 7.75 in² per 3'-3" are located at the lowest and highest point of the façade cladding, as well as in windowsill and window lintel areas, and penetrations.
Thermal insulation in winter
The flow of heat which moves outwards in winter is measured using the so-called thermal transmission coefficient (U-value). The lower this value, the less heat that will dissipate outwards. The U-value depends on the thermal conductivity of the heat insulation and the thickness of the insulating material. The high-quality heat insulation stipulated by EnEV (Energy Saving Ordinance) makes a contribution to environmental protection and will soon pay for itself with lower heating costs.
Insulating materials made of mineral wool according to DIN EN 13162 type WAB should be used here. Proper installation of the insulating layer reduces heat losses.
It is advisable to avoid thermal bridges, i.e. components that take up and transmit the cold more quickly than other elements, or to try and minimize their effect on adjacent parts of the building. Energy losses due to the thermal bridge effect of anchorings and fixings should be taken into consideration when calculating the thermal transmission coefficient (U-value /energy balance).
In addition to the well-known design-specific thermal bridges occurring in buildings, e.g. cantilevered balcony slabs, installation of the substructure must be taken into account with rear-ventilated facades. If the substructure is made of metal, a major reduction in such thermal bridges can be achieved by including an insulating layer between the supporting structure and wall bracket (thermal break). Substructures made of wood, as normally used for facade claddings with the seaming technique, are nowadays built with crosswise battening due to the insulating thicknesses required. This too results in a reduction in thermal bridges.
Another influencing factor is the degree to which a building is windproof. If the building envelope is not tight (suction/pressure from wind), this will result in high ventilation/energy losses, as well as draughts (unpleasant indoor climate). It must be ensured that the building is windproof prior to installation of the rear-ventilated facade. This requirement is satisfied by solid masonry and concrete. Penetrations (e.g. windows, ventilation pipes, etc.) must be windproof from the building components to the supporting structure.
Building codes should be consulted for the amount and type of insulation required for the project.
Thermal insulation in summer
In summer, thermal insulation prevents the interior of a building heating up to an unacceptable level due to direct and indirect solar radiation. This is described in DIN 4108-2 and EnEV.
The aim here is to minimize the flow of heat which moves into the interior of the building. Once again, good heat insulation and a solid design will help here. The advantage of rear-ventilated curtain-walling is that a large part of the heat radiating onto the cladding is dissipated by convective air exchange.