Presented by David Hill, President, Eneready Products
Relative humidity is a measure of moisture content in the air compared to the maximum that air could hold if it were fully saturated (i.e. steamy bathroom).
Absolute moisture, a less used but still important term, is a measure of weight in 'grains of water' contained in 1 pound of dry air.
Maintaining the correct relative humidity (RH) is important for the health of:
a) the residence itself and
b) our ultimate customer, 'Ms Smith' its owner/occupant.
Although the 2 ideal RHs levels are slightly different, the difference between them is small and in good buildings, a compromise will satisfy both. HVAC systems are a part of the solution, but unfortunately only 1/2 of that required for effective RH control. The builder's attention to detailing of the air barrier and insulation layer is critical, but that is not always done well.
Due to ground breaking research at the Vancouver Test Hut, (read Leaky Condo Research Project) Mark Gauvin (builder) and Dr. Joe Lstiburek P.Eng. (researcher) have shown that wood frame homes, an inherently affordable method of construction can satisfy both and provide decades of good service if they are:
a) externally insulated,
b) have an effective (sealed) air barrier and in when located in coastal areas
c) have a ventilated rain screen (cavity) incorporated beneath the exterior cladding.
In a building devoid of either or both a) & b) above, if we were to forcibly raise the relative humidity in aide of Ms Smith's lung health, the risk of damage to the house is real and will likely show up with:
a) excess moisture in the attic and/or
b) mildew/moisture in cool dead corners of closets and basements ultimately compromising respiratory health.
In defence of adding RH is winter, Dr. Stephanie Taylor's recent research has shown that our natural human immunity against infectious bacteria and viruses increases when relative humidity levels rise above 40% in a well-built home, a good HVAC system will have an effect and can:
- Lower RH using ventilation in the winter and A/C in summer and
- Raise RH with humidification. While in winter this will increase the moisture stress across the exterior wall and ceiling this can be done, in moderation without risk
David Hill will share his experience and first-hand knowledge on this often misunderstood topic.
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