Exploring Building Envelope Innovations that Improve Indoor Air Quality

Achieving a tight building envelope is the new objective for many homebuilders and homeowners. A systems-wide approach combining thermal insulation techniques, various construction types, and high-performance water and vapor barriers can change a home's energy efficiency.

Starting with a properly designed building envelope does wonders for helping the home's HVAC system perform more efficiently and provide even greater control in reducing unwanted temperature variations.

As the International Energy Conservation Code (IECC) adopts stricter energy considerations, homebuilders are increasingly concerned with eliminating air leaks that allow cooler, conditioned air outside, and stale air inside.

But, as homebuilders concentrate on a tight building envelope and fight air leakage, indoor air quality can suffer. 

“Once you start sealing and tightening a house, you have to think more about how moisture and chemicals inside will be controlled,” said Brian St. Germain, Director of Siding Technology at LP Building Solutions.

Moisture collects inside a home as it's being lived in. Actions like showering, cooking, running water, and opening doors and windows all contribute to moisture collection. Additionally, moisture can enter the home as warm humidity in the morning, then settle and condense on any cold surface. This condensation has a potential for cultivating mold and mildew inside the home.

"When a house is sealed, it doesn't breathe well," said St. Germain. "That's by design. You don't want it to breathe, you want it to hold air. It's important to consider that air permeability and vapor permeability are two separate things. Something can be airtight and hold in air. But it can still transfer moisture."

“Maintaining moisture levels is the key to achieving good indoor air quality. And one way to do that is to use a high-performance barrier like LP WeatherLogic^® Air and Water Barrier. It's an air barrier, but it's permeable to allow moisture vapor to escape,” said St. Germain. 

LP WeatherLogic Air and Water Barrier combines sheathing and a weather-protective layer in a single panel that can be installed just like regular sheathing. The panels feature an ASTM E96 tested vapor-permeable overlay permanently integrated into the panel that allows moisture vapor to escape rather than getting trapped inside walls. 

Some contractors prefer to use drywall as the air barrier, but there are so many places that come together that have to be sealed to prevent air leakage. Using products like the LP WeatherLogic Air and Water Barrier gives builders the desired tight building envelope.

"Concentrating on indoor air quality is good. But it's more important to frame it as 'maintaining moisture levels,' as a means of achieving good air quality," said St. Germain.

Indoor air quality testing is performed by an air leakage test, which uses a calibrated fan to determine air pressure. "You're looking at how hard that fan has to work to measure air pressure inside and outside the house," explained St. Germain.

For homebuilders who have achieved a tight building envelope yet want to further improve home air quality, St. Germain recommends installing an energy recovery ventilator (ERV). These systems blow stale inside air out while bringing in fresh air. The two air streams cross paths but do not touch. In winter, the warm air leaving the house heats the air coming into the house. These systems are more common in cool climates, and are finding greater popularity in humid climate belts around the U.S.