Passive House

When reading about Passive House you will come across the name Prof. Dr. Wolfgang Feist and his Passive House Institute in Germany. Dr. Feist and his research institute are setting standards for building houses with an annual energy consumption of less than 10 kWh/m2 per year.  These are houses that need very little heating in winter or cooling in summer. This is made possible by superior isolation of floors, walls, and the roof as well as technology to recycle energy that is already in the house. This requires also superior windows and doors, which when closed, keep the temperate in the house at a comfortable level without much additional energy use.

The VEKA Window System offers solutions that are fully compliant with these advanced standards. With the proper glazing and the excellent VEKA frames you can reach U values below 0.7 W/m2K. However, a passive house with such objectives requires a highly sophisticated ventilation system to ensure that the energy is not lost through open windows. The German Passive House Institute provides extensive information on their website.

VEKA recommends windows built with MD82 window frame profiles and triple glazing with Argon gas filling and Low-E coating for the lowest thermal transfer coefficients.

Thermal profile of VEKA SOFTLINE MD82

Thermal transmission of a window

The right combination of the uPVC window system and glazing solution is not only important for the perfect insulation, but also helps to avoid mold at the window and water condensation at the inside glass pane, which might damage the interior of the apartment.

This image shows the typical thermal distribution for a VEKA MD 82 system window profile with -10 degree Celsius outside and +20 degree Celsius inside room temperature. Different colors symbolize different temperatures. The blue line shows the 10 degree Celsius line, which is the temperature zone where mold grows. This 10 degree line is fully inside the uPVC profile and mold will not form on uPVC. The red line is the 13 degree Celsius temperature line. 13 degree Celsius is the border temperature, where water will condense at the glass panes and might run down to the window sill and damage the interior of the apartment. With the extra high glazing beads of 25mm in VEKA’s SOFTLINE 82mm system, this critical 13 degree line is covered entirely by the glazing bead and continues to run between the glass panels. This design avoids water condensation at the glazing and protects the interior of the apartment.

VEKA SOFTLINE MD 82 PSR has been certified by the Passive House Institute with a Uw: 0.80 W/(m2 K) for the climate zone “cool and temperate”

Calculation of a Window’s U Value


Heat transfer coefficient of the whole window (W/m2·K)


Heat transfer coefficient of the glass (W/m2·K)


Visible area of glass (m2)


Heat transfer coefficient of profile frame (W/m2·K)


Visible area of profile frame (m2)


Linear heat transfer coefficient of the connected spacer (W/m·K)


Boundary length of the glass (m)


Visible area of glass (m2)


Visible area of profile frame (m2)


The effect of spacer on Uw value

A Aluminum Spacer
Ψ = 0.078
Uf  = 1.3 Uw = 1.07 Uf = 1.2 Uw = 1.05 U= 1.0 Uw = 0.99
B Warm edge Spacer
Ψ = 0.030
Uw = 0.95 Uw = 0.93 Uw = 0.87
Reduction (%) 11.2% 11.4% 12.1%


VEKA SOFTLINE MD70 NEO with tripple glazing

Glass Performance Table

Glass Configuration Glass Thickness
Visible Light Transmittance T% Shade Coefficient (SC)
5+12A+5 22 2.83 81 0.88
5+14A+5 24 2.76 81 0.88
5+12Ar(90%)+5 22 2.66 81 0.88
5+9A+5+9A+5 33 1.90 74 0.78
5ssLow-E+12A+5 22 1.81 71 0.67
5+12A+5+12A+5 39 1.74 74 0.78
5ssLow-E+14A+5 24 1.59 71 0.67
5ssLow-E+12Ar(90%)+5 22 1.40 71 0.67
5ssLow-E+14Ar(90%)+5 24 1.32 71 0.67
5ssLow-E+9Ar(90%)+5 +9Ar(90%)+5 33 1.26 71 0.61
5ssLow-E+12Ar(90%)+5 +12Ar(90%)+5 (WES) 39 1.16 71 0.61
5ssLow-E+12A+5ssLow-E +12A+5 39 1.05 69 0.56
5dsLow-E+12Ar+5dsLow-E +12Ar+5 (WES) 39 0.81 54 0.38
5ssLow-E+16Ar(90%)+5ssLow-E +16Ar(90%)+5 (WES) 47 0.75 69 0.56
5dsLow-E+16Ar(90%)+5dsLow-E +16Ar(90%)+5 (WES) 47 0.67 54 0.38

ssLow-E: single silver Low-emissivity coated glass
dsLow-E: double silver Low-emissivity coated glass
A: Air layer
Ar: filled with more than 90% Argon
WES: Warm Edge Spacer


Passive House Wall

Thickness: 490-640mm
U-Value:0.22 – 0.14

Brick Wall

Thickness: 280mm

Concrete Wall

Thickness: 340-400mm
U-Value:1.45 – 0.45


Aluminum Window with Thermo breaker

Thickness: 50-70mm
Uf: 2.6 – 3.5
Uw: 2.2 – 3.2

VEKA 82mm System Window

Thickness: 82mm
Uf: 1.0
Uw: 0.8 – 1.5

VEKA 70mm System Window

Thickness: 70mm Uf: 1.3 Uw: 1.3 – 2.0

DescriptionWall ThicknessWall Insulation ThicknessTotal Wall ThicknessU-Value Material
Brick Wall280 mm280 mm1.20
Concrete Wall340 mm340 mm1.45
40 mm380 mm0.58
50 mm390 mm0.50
60 mm400 mm0.44
Concrete Wall (Passive House)340 mm150 mm490 mm0.22
220 mm560 mm0.17
300 mm640 mm0.14
DescriptionProfile DepthUfUgGlass ConfigurationUw
Steel Window30 mm4.005.705 mm single glass≥ 5
Aluminum Window40 mm4.002.905+9A+53.5
Thermo Break Aluminum Window with 14.8mm spacer50 mm3.502.705+12A+53.2
Thermo Break Aluminum Window with 20mm spacer60 mm2.901.755ssLow-E+12A+52.3
Thermo Break Aluminum Window with 27mm spacer70 mm2.601.505ssLow-E +9A+5+9A+52.1
VEKA 70mm System Window70 mm1.302.505+14Ar+52.4
VEKA 82mm System Window82 mm1.000.805ssLow-E+16Ar (WES)+ 5ssLow-E +16Ar (WES)+50.97

ssLow-E: single silver Low-emissivity coated glass
A: Air layer
Ar: filled with more than 90% Argon
WES: Warm Edge Spacer

Reduction in % of energy usage per sqm living area over the years. Base 1981= Energy Usage equivalent to 25kg of Coal per sqm

Building Regulations in Asia

Most governments in Asia started to realize the importance of improved insulation of buildings to save energy and protect the environment. Ever higher insulation rules have been issued and enforced in Korea and China. For example the Chinese government has realized that a lot of energy can be saved with thermal isolation and has issued strict guidelines for the U-values of windows, doors, walls etc. The stipulated U-values are the highest (worst) U-value allowed but must be even better (lower) if the window/wall ration is more than 20% (most buildings have a 30%-40% window/wall). These regulations must be followed by new construction projects as well as renovation projects.

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