A Window on Your Health
How is a Passivhaus Window Good for Your Health?
Typical windows transmit more heat than walls, therefore, the windows are cooler than the adjacent wall surfaces. This makes them both uncomfortable and bad for your health.
The colder surface temperature means that the relative humidity on the window surfaces can be high enough for condensation to occur. I see this in my non-Passivhaus house very regularly and I am sure you will have seen it also. Condensation brings with it the risk of mould and the associated dangers to our health. This is part of the reason why asthma rates are so high in countries like the UK and NZ. (I’ve written about this before here and here particularly.)
Passivhaus Windows eliminate this risk. The integrated design approach of the international Passivhaus Standard encompassing the high-performance thermal envelope, thermal bridge free construction, airtight construction, good ventilationand high-performance windows ensures a condensation-free indoor environment. This is a healthy and mould-free environment that all people would benefit from.
For certification of Passivhaus windows, the coldest point on the window frame (typically in a corner where there is both frame and spacer) must not have a “water activity” of greater than 0.80. What this means, is that the relative humidity (RH) at the surface of the material, or just below it, must not exceed 80%. Mould growth can start once the surface RH exceeds 80%. The certification criteria include climate-specific values for the internal surface temperature factor (fRsi) which ensures the relative humidity is acceptable.
The relative humidity increases as the surface temperature goes down, so a healthy surface RH is directly related to the window staying warm. The internal surface temperature is directly related to the installed window U-value. So although energy efficiency is the means, in this case, hygiene and a healthy indoor environment are the outcomes.
Passivhaus windows provide a healthy hygienic mould-free indoor environment.
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