“Houses need to breed” is the biggest misconception in the building industry and the most heated topic among builders. Years of building practice are clashing with latest trends and recommendations among building science researchers. Houses need to ventilate, yes, but not to breed. While ventilation can be achieved through leaky assemblies (walls) there are too many downsides for us to accept this method. When ventilating through wall assemblies, dust, mold spores, allergens and impurities are introduced to the interior air. Ventilation is not uniform through the building resulting in over ventilated and under ventilated areas. There is more “ventilation” during windy and stormy days than during calm weather. When such substandard building practice is performed in association with substandard mechanical design, results are dry interior air, high heating cost, sensation of cold penetrating the structure, presence of the mold inside wall cavities and so on.
There are several reasons why warm, humid air escapes home and cold dry air (in the winter months) enters the home. They range from leaky heating ducts being outside of the thermal envelope, pressurizing some areas of the house, air leaks around dryer duct, electrical conduits, plumbing, crawl space and basement penetrations, stack effect etc. Every time warm moist air escapes the home (like by being pushed out of the leaky duct in the attic), cold dry air enters somewhere else. This is a reason for the second biggest misconception in the building industry: “Furnaces dry out the air” and “wood stoves give out dry heat”. Neither one dries out the air, they blow humid, warm air out and it gets replaced by dry, cold air. Results are an uncomfortable interior environment and increased heating bills. This setup is shown on the picture. Dry air is often being humidified with vapor humidifiers. Results are high moisture in one area of the home, high moisture in the walls of the same area of the home and high potential for condensation, water and mold presence in those wall cavities.
We at Mountain contracting builds tight houses, with air infiltration ranging from 1 to 2 air changes per hour when tested with 50 Pascals of negative pressure blower door test. We control fresh air using a heat recovery ventilator and we prevent moisture from escaping the thermal envelope. Results of this approach are reduced heating and cooling bills and a comfortable, uniform interior environment that is free of dust, allergens and mold spores.
