It also has real implications for our tighter homes with fewer air changes per hour.
A recent post in TreeHugger quoted a study on chemical exposures in “green” low income housing and found, unsurprisingly, that if there is no ventilation, then you can get a buildup of Volatile Organic Compounds (VOCs) that is neither healthy nor green. But how much ventilation do you need? And is it a constant or does it change over time? Another fascinating study by a team led by Susana Hormigos-Jimenez, Ventilation rate determination method for residential buildings according to TVOC emissions from building materials, looked at this, noting right at the start:
People spend most of their time indoors in residential buildings; thus, maintaining good indoor air quality (IAQ) is essential. It is necessary to provide a suitable ventilation rate in these spaces (low-density occupation) taking into account that materials (finishes and furnishing) are one of the main sources of indoor pollution.
This summarizes what people involved in green and healthy building have known for years: You need good controlled ventilation, and you should build with stuff that doesn’t fill the home with VOCs. But the study also shows that the situation changes over time.
The authors analyzed the contents of a typical room, the materials it was made of and the furniture in it -- closets made of plywood, flooring, both laminated wood and carpet and foam underpad on plywood, furniture made of maple. They found that the age of the materials had a big impact: “Most of the health hazards associated with VOC emissions occur during the first few months of building use or after remodeling, as the highest concentrations of VOCs are found in new or renovated buildings.”
To get the room down to acceptable standards of TVOC, the laminated flooring required the highest rate of ventilation for the longest period, the plywood for a shorter period, and the maple furniture needed the lowest ventilation rate, which is one reason we love vintage furniture!
Significantly, it took over six months for the ventilation level required to get down to 200 micrograms of total VOC per cubic meter concentration (The European standard). It also shows that people who design really tight houses have to think about what they put in them, because the air changes needed here for at least the first few months are way higher than what these houses are being designed for.*
It should be noted that the study was based on data from a National Research Council of Canada database, and not from a real room. “In real situations, VOCs concentration, temperature, humidity and airflow levels may fluctuate, suggesting that the emissions estimated under laboratory conditions may not adequately demonstrate real behavior.“
The researchers conclude:
This study shows the differences in the requirements established for a good IAQ and how this has a significant influence in establishing a specific value or range of values for an appropriate ventilation rate. It is necessary to unify the criteria in this field in such a way that regulations are created based on the main sources of pollution, that is, considering the building materials located in spaces with low-density occupation; and setting a maximum allowable overall concentration to ensure the occupants' safety of a building in terms of health, by means of a good IAQ.
But as our homes are built to ever tighter standards, it is becoming increasingly clear: Our material and furnishing choices matter, and you can’t build a healthy home without considering them. And also, importantly, air change rates are about more than just energy efficiency; they are also about air quality.
*There have been a couple of updates to the section on air changes and tight houses, and I am still working on this section. Air change math is hard.