When You Build it Tight You Have to Ventilate Right
Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation
If changes are made to an existing home in terms of tightening the building envelope and you see changes other than your utility bills going down, pay attention to the details because they may be a warning sign that you have not properly ventilated the home.
Lack of adequate ventilation in a home can result in serious problems. The more obvious one that appears in obvious places is elevated humidity. If you are sweating the inside of new insulated glass windows in the winter when you didn’t before then your interior humidity has gone too high. Another warning sign is dirt stripes appearing on the walls in front of the studs. Musty odors, sweating or condensation, or unusual patterns on your walls could be indications of a ventilation problem.
However, moisture is not the only concern. You also need to be concerned about gas concentrations in the air because of the dangers associated with them and the build up of volatile organic compounds (VOCs). VOCs are emitted from many products that exist around the home but if you tighten up a home and don’t provide adequate fresh air, they are now being trapped within the home. Many volatile organic compounds breakdown with exposure to ultraviolet (UV) light outside the home – formaldehyde for example has a half-life of about 14 days – but inside the home UV light is diminished and so has little affect on the concentration of the VOCs. VOCs could be coming off of products which you would never suspect. For example, some citric acid cleaners that smell like orange can have amazingly high VOC concentrations. Remember, what has changed in the equation is the amount of fresh air that had been there before that helped evacuate these things from the home. The standard furnace filters we employ do not filter out gasses – they filter particles.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (AHRAE) has very specific guidelines on how much fresh air is needed for a healthy environment. ASHRAE 62.1 references the calculations for commercial buildings and ASHRAE 62.2 is for residential buildings. It is critical to review these guidelines in order to properly ventilate the building envelope especially if you are making changes. When homes are tightened for energy efficiency you must make sure that adequate fresh air ventilation is taken into consideration. There are many ways to do this that are compliant with the ASHRAE recommendations. And remember, if you find signs of moisture it’s like the canary keeling over in the coal mine. Heed the warning!