Why are wooden windows the better choice?
As well as the use of aluminum in wide shop-windows and PCV windows in office buildings appears to be the fitting solution, wooden windows should be used in residential and historical buildings. Economic reasons as well as the trust in natural materials are here important. Authorities in Western European countries advise the use of wooden windows when renovating old buildings as well as in public buildings (especially if children are present) and these are also subsidized.
The insulation qualities protecting against energy loss through the windows are especially important for economic reasons. The measure of the thermal insulation is the heat transfer coefficient "U". According to the simplified procedure PN-B-02025 from 1998 the heat transfer coefficient for walls in buildings is Umax = 0.30 [W / (m²K)] and for windows Umax = 2.0 to 3.2 [W / (m²K)]. It must be emphasized that the heat transfer coefficient for wooden window frames is U=1,2 to 1.3 [W / (m²K)]. This value is gained only by the thermal insulation qualities of the wood, which other materials used in the production of wooden frames do not possess. The increase of the coefficient "U" for the whole window depends on the heat transfer through the glazing. The thermal insulation quality of the windows against heat loss collides to a certain extend with the window weathertightness, which is related to the necessary air exchange.
“According to regulation of the technical conditions, to which buildings and their location should apply" (Law gazette No. 15 from the year 1999) the problem of the window sealing is addressed as follows: (Section 148.2) " If windows, balcony doors and other closing devices of openings to the exterior with high weathertightness are used, which inhibit a penetration of the outside air to such an extent which would be necessary for ventilation requirements, a suitable device which guarantees a sufficient air supply into the interior must be applied". In subparagraph 2.3.3 of the exhibit with the title "Requirements for thermal insulation and other requirements for the energy savings" is written: "In residential buildings and public building the air exchange rate for opening windows and balcony doors in rooms, in which the inflow of the outside air is guaranteed by window ventilation, may be not greater than 0.3 m³ / (m*h*daPa2 / may amount to 3), and in other cases more than 0.5, but no more than 1.0 m³ / (m*h*daPa2 / 3). Plastic windows have an air exchange rate in the range of 0,1 to0.2 m³ / (m*h*daPa2 / 3), their application in buildings requires the use of additional devices which guarantee a constant air inflow.
The last function of a window, which must be mentioned, is noise prevention, thus, sound insulation or sound absorption. Windows with the usual two chamber composite panes (4 3 4 / 12 12) with an air filled space between the panes should have a sound insulating coefficient of at least Rw = 30 dB (according to PN-EN 20140-3: In 1999) to qualify these windows for sound insulation. To improve the sound insulation, thicker glass can be used. The space between the panes can also be filled not with air, but with gas, e.g. argon. Nevertheless, the fact is that wood has very good insulation qualities and fulfils the requirement on sound insulation excellently. It must be said that only in the case of wooden windows the panes are sealed permanently in the window frame with silicone, which connects the pane with the frame mechanically. This is possible, because the measures of the wooden frame at different ambient temperature do not change. Other materials which are used for the production of windows do not fulfill these requirements.
Metal and plastic windows, which are applied in building walls facing the sun, are exposed to certain changes of their metrics that can clearly complicate the window opening and window closing. Nevertheless, wood swells and deforms due to humidity. This effect can be eliminated through the use of layer laminated timber for retension. The deformation is avoided through the coating of the window frames and casement. Thus, the wooden surface is protected by preventing the entry moisture.
 |
Window construction:
|