A high standard of insulation as an important component of the energy turnaround
Hardly any component in a building has made such rapid progress in the field of thermal insulation as the window. Within twenty years, the U-value has improved from 2.6 to less than 1.0. The industry has made many adjustments, optimizing each window element individually. Triple glazing is now standard for a highly insulated house. This is complemented by integrated insulating inserts made of extruded polystyrene (XPS) or cork in the window frame, inert gas fillings in the spaces between the panes and thermally optimized edge seals.
Inert gas filling replaces air filling
Until 1995, the filling between two panes consisted of air. Laboratory tests have shown that the inert gas argon has a thermal conductivity (λ value) that is one third lower than that of air. In addition, argon achieves the U-value 0.7 with a space between the panes of 13 to 14 millimeters, while air requires a space between the panes of 18 and 20 millimeters. Krypton and xenon have even more favorable properties in terms of thermal conductivity. However, these two noble gases are considerably more expensive than argon.
Low-ε coatings and a thermally optimized edge seal
Thermal glazing can no longer do without a wafer-thin metallic coating on the inside of the pane. This so-called low-ε coating improves the U-value of the glazing from 2.4 to 1.2, all other conditions being equal. The coating has the task of not letting the long-wave infrared light out. Coatings improve the window quality not only of triple-glazed windows, but also of double-glazed windows. A thermally optimized edge seal ensures that the spaces between the panes are absolutely tight. The edge seal is made of butyl on the sides and polysulfide on the horizontal. In between, the edge seal contains a desiccant with two diffusion openings at the top edge.
Wooden frames with insulating elements also provide good thermal protection
Plastic window frames are made of a relatively soft material. They achieve their high insulating effect through 5 to 7 chamber profiles, which, however, require a stabilizing core. In addition, insulating elements can be installed in the chambers. The insertion of insulating elements is now also possible for wooden windows. As a result, U-values for the frame of less than 1 can be achieved. Soft wood such as pine or larch insulates slightly better than hard wood such as oak or meranti. The thermal insulation of a wood-aluminum composite can also be improved by insulation elements.
Soundproof windows require even more effort in glazing
A four-millimeter-thick float glass would be sufficient for good thermal insulation properties. However, in terms of sound insulation, this only achieves the lowest sound insulation class at around 30 decibels (dB). For a 4 dB increase in sound insulation, the pane thickness of a double-glazed window would have to be six millimeters. A further increase to 37 dB is achieved by arranging different pane thicknesses. For example, a double-glazed window could have the combination 8/16/4 instead of 6/16/6. For a triple-glazed window, the combination 8/12/4/12/4 would result in a sound reduction index of 37 dB. There is also a side effect to consider: the weight of a window in sound insulation class 3 is around 10 kilograms per square meter higher than in sound insulation class 1.
Installing windows professionally
The best window quality will fizzle out if the installation in the building opening is not carried out professionally. A ten millimeter wide connection joint should be provided all around the window. The joint must then be sealed to be driving rain-proof and airtight. Pre-compressed sealing binders or tested installation foams are suitable for this purpose. The private Institute for Window Technology in Rosenheim shows in numerous tutorials what special attention must be paid to when installing windows. The Quality Association for Windows, Facades and Front Doors awards the RAL seal of approval, which allows specialist companies to demonstrate their competence in window installation.