Houses need ventilation to breathe. Proper ventilation makes a home more comfortable. Areas needing ventilation are attics, crawl spaces or any other unconditioned space that meets a conditioned space. Poor ventilation can cause dark stains to develop on the attic sheathing boards. Some homeowners practice “out of sight, out of mind”. They do not go into those spaces so there is no problem. Unfortunately, the first indication of a problem is a major one. I suggest looking in these spaces at least once a year.
Attic ventilation is most important and comes in many forms. There are passive vent products: ridge vent, roof vent, soffit vent, gable vent and turbine vents. They rely on the outdoor weather to perform. There are active vent products: thermostatically controlled roof mounted attic fans, ceiling mounted whole house fans, and window fans. They use power to move the air where it is needed.
Poor ventilation occurs when there is not enough air turnover. Attic vents are too few, clogged with debris, or improperly spaced. Bathroom exhaust fans should discharge outside. Those that discharge to the attic contribute to the moisture that leads to dark stains. Signs of poor ventilation start as small dark stains around the roof shingle fasteners that penetrate the interior of the sheathing boards. At this point, the repairs generally consist of additional attic vents, and bath vent pipe re-routing. Left unchecked the stains grow until all of the sheathing boards are covered. At this point, the dark stains may have compromised the structural integrity of the roof sheathing boards. Complete roof shingle and sheathing board replacement may be necessary.
ASHRAE (formerly the American Society of Heating, Refrigerating and Air-conditioning Engineers) has a standard 62.2-2016: Ventilation and Acceptable Indoor Air Quality in Residential Buildings. It says that residential buildings should have a minimum of 0.35 air changes per hour but not less than 15cfm (cubic feet of air per minute) per person. All houses must breathe, if the house is too tight, mechanical ventilation can be added to help improve air changes per hour. These systems are called heat recovery systems or energy recovery systems. They are programmed to operate for so many minutes per hour. I have one that runs 8 (12%) minutes per hour, unless I manually increase it. Here’s a tip: if you have one and your windows are open in the summer like mine, disconnect the ventilator. Remember to reconnect it when the windows are closed.
If you think you have unhealthy air in your home contact a qualified HVAC or Environmental company. They can help determine what, if any, recommendations are needed to make the house more comfortable, healthy and happy. They may recommend additional passive vent products, or installing an active vent product. Either way, you will feel better.