Suf­fi­cient insu­la­tion is achieved through the use of tech­nolo­gies such as:

  • using lay­ered glued wood
  • prop­erly designed seals
  • proper instal­la­tion

Insu­la­tion of win­dows, U-​factor

What exactly is this U factor?

It is a heat trans­fer coef­fi­cient for a struc­tural ele­ment (e.g. wall, win­dow, etc.) It shows the amount of heat loss (1W) from the inte­rior to the exte­rior over a sur­face of 1m², with a dif­fer­ence in tem­per­a­ture of 1°C (1 K).

Con­duc­tive mate­ri­als, such as met­als, have a less favourable value of this coef­fi­cient in com­par­i­son to insu­lat­ing mate­ri­als, such as poly­styrene, min­eral wool or insu­lated glass, which have a lower U value and there­fore insu­late bet­ter. Heat losses in such rooms are in effect smaller.

The unit used to describe the heat-​transfer coef­fi­cient U is W/(m²K).

The heat trans­fer coef­fi­cient is a very impor­tant para­me­ter for struc­tural par­ti­tions – heat losses can be deter­mined for a given par­ti­tion on its basis. The coef­fi­cient value depends on the type and thick­ness of the mate­r­ial from which walls, win­dows are made, but also on the nature of the partition.

The heat trans­fer coef­fi­cient for the par­ti­tion is cal­cu­lated based on the heat resis­tance coef­fi­cient of the ther­mal resis­tance of the par­ti­tion and an allowance for insu­la­tion leaks and ther­mal bridges.


What a buyer should look for when com­par­ing U coef­fi­cients for windows?

  1. Each win­dow has, depend­ing on its size and qual­ity, its own heat trans­fer coef­fi­cient (coef­fi­cient Uw.) 10 win­dows = 10 dif­fer­ent heat trans­fer fac­tor val­ues. This is also possible.
  2. The big­ger the win­dow, the bet­ter its Uw fac­tor and vice versa. This stems from the fact that the glass and frame have dif­fer­ent heat-​transfer U-​factors. In other words, more glass panes = warmer win­dow, but not vice versa. The con­clu­sion from this is that the right choice of win­dow panes is very important.
  3. Accord­ing to the stan­dard, the max­i­mum U-​factor for win­dows in a façade is 1.8 W/(m²·K) – for the I, II and III cli­mate zones and 1.7 W/(m²·K) – for zones IV and V. Mod­ern win­dows are, how­ever, warmer and have a much lower, that means bet­ter, U-​factor value. Win­dows installed in energy effi­cient homes should have a U fac­tor no greater than 1.3 W/(m²·K), but noth­ing stands in the way of them being even warmer. Pas­sive win­dows are char­ac­terised by a U-​factor no greater than 0.8 W/(m²·K).
  4. In the case of newly con­structed build­ings, the designer or archi­tect is obliged to present the com­pany offer­ing win­dows a Uw-​factor value for each ordered win­dow. That is because only it cal­cu­lates the total energy con­sump­tion of the con­structed build­ing and deter­mines the build­ing mate­ri­als and work method, through which the build­ing is to have the energy inten­sity class and energy class of build­ing or apart­ment as per the design. This is some­thing you should demand from devel­op­ers, designers.
  5. Com­pa­nies sell­ing win­dows have an oblig­a­tion to mark win­dows with an indi­ca­tion of the heat-​transfer fac­tor for each ordered window.
  6. Warm instal­la­tion as per the require­ments of the stan­dard is very impor­tant, if 100% of the ther­mal insu­la­tion capac­ity of mod­ern win­dows is to be used.

Energy sav­ing windows