It has taken years for building scientists and progressive builders to get past the “buildings need to breathe” nonsense and replace that with a more helpful mantra: “Build Tight, Ventilate Right.”
Leaky buildings invite problems, including unnecessary energy consumption, drafts, and the potential for moisture accumulation inside walls and roofs. Houses with low rates of air leakage don’t have these issues, but as the natural exchange of indoor and outdoor air decreases the need for mechanical ventilation goes up. Off-gassing VOCs from building materials and furnishings, fine particulates from cooking, combustion gases from kitchen ranges and heaters, and a variety of other pollutants all contribute to unhealthy indoor air.
Mechanical ventilation has two important benefits. It brings in fresh, outdoor air that dilutes the concentration of indoor contaminants, and it collects moisture and pollutants at their source and vents them to the outside before they can spread throughout the house.
In an introduction to this topic , the Lawrence Berkeley National Laboratory (LBNL) points out that it’s not possible to monitor indoor air quality to know when ventilation is needed and when it’s safe to go without. “The best protection is providing background ventilation to constantly remove indoor air and replace it with fresher outdoor air,” the lab notes, “and to provide extra ventilation equipment where pollutants and moisture are commonly produced (the kitchen stove, bathrooms, laundry rooms, hobby areas).”
Spot ventilation where it’s needed, and continuous whole-house ventilation, are the foundation of an effective ventilation system. Homeowners have many choices for each, ranging from simple to elaborate, all with pros and cons. The topic can become surprisingly complex, inviting experts to haggle over the smallest details (a post originally published at GBA in 2009 and updated in 2018 collected 117 comments from readers, collectively many times longer…