Offsite Modular Construction and Indoor Air Quality

Comfort, health, and safety are important when you are building a new home today. What issue encompasses all three of these items more than Indoor Air Quality? We are building homes so efficient today that in many cases, the indoor air quality (IAQ) is worse than outside air quality. Don’t believe it? According to the EPA, the levels of indoor air pollutants are often 2 to 5 times higher than outdoor levels. In some cases, these levels can exceed 100 times that of outdoor levels of the same pollutants! Let’s examine what you can do when building your new home to protect you and your family.

Drawing the Line – Creating the Thermal Envelope

In a home, the building enclosure or building shell is what separates the inside from outside. But there are two types of space inside of your building shell. They are known as conditioned space and unconditioned space. For example, in many homes, attics and crawlspaces are unconditioned space. Typically the floor(s) between the two areas is conditioned space. The boundary that separates these two areas is known as the thermal boundary or thermal envelope.

When creating an energy-efficient home, it is important to eliminate or reduce the holes or leaks in the thermal envelope. In real-life construction, unsealed areas around doors and windows can leak air into the home. And then there are the holes we make on purpose: dryer vents, bathroom exhaust vents, exhaust fans over the stove, and even fireplaces. Modular construction is great at minimizing and eliminating holes in the thermal envelope. Building in a controlled, indoor environment means you can close and seal holes for items like wires, pipes, etc. in a consistent manner. (I know the EPA said outdoor air is better than today’s indoor air. Just hold on a bit. We’ll get to that soon.)

The Causes of Bad Indoor Air

Indoor air quality is important. Babies, children, and the elderly are especially susceptible to respiratory issues. Everyone benefits when the home they live in is free of pollutants. Here are just some of the most common air pollutants:

• Toxic materials such as lead, pesticides, and asbestos
• Biological pollutants such as mold and mildew
• Natural contaminants such as pet dander and radon
• Combustion byproducts such as tobacco smoke and carbon monoxide

Again, modular construction helps mitigate or eliminate many of the bad things that can happen in your home when it’s constructed. Think about the last time you drove by a home that was being built on a rainy day. Remember the water puddled on the floor and the walls that were soaking wet. Well, they don’t always dry out before the roof goes on and the drywall goes up.

Another issue that happens frequently is that during onsite construction, dust and dirt collect on the floors. A laborer is then told to sweep it up but takes the easy way out. Yes, it gets swept into an open floor register. That dust and dirt are now propelled into the air you breathe every time the furnace or air conditioner comes on. This can happen for years after the home is completed. Modular construction means your home is always dry. It never rains on your home so mold and mildew are missing the moisture needed to grow. Labor is closely supervised. Your ducts are free of debris.

Measuring a Homes “Leakiness”

A blower door test provides the ability to measure air leakage in a building. An exterior door is opened and a blower door device is installed. In and of itself, a blower door test isn’t a high tech testing method. It doesn’t isolate any one system in a house or tell you where holes are. Rather it is a method to determine how leaky all systems working together actually are. You will hear the term ACH 50. This is a measure of how many times the Air Changes per Hour at a pressure of 50 Pascals. While it sounds technical, it is a common way to measure the “leakiness” of a home.

Sealing leaks means:

• Avoiding moisture condensation problems
• Avoiding uncomfortable drafts caused by cold air leaking in from the outdoors
• Determining how much mechanical ventilation might be needed to provide acceptable indoor air quality

Letting in the Fresh Air

When a home is sealed below 4 ACH 50 it means that it should be mechanically ventilated. Otherwise, the people living inside can suffer from stale air, and moisture problems can arise.

There are two common devices used to ventilate a home mechanically, a Heat Recovery Ventilator and an Energy Recovery Ventilator. They are designed specifically to trade fresh air for stale air and, at the same time, minimize the loss of energy in the process.

Heat Recovery Ventilator (HRV) – An HRV uses an exchange core to pass heat from one airstream to the other. The exchange core in an HRV can be aluminum or plastic. This core prevents indoor moisture and odors from crossing into the flow of fresh, outside air.

Energy Recovery Ventilator (ERV) – ERVs are the same as HRVs except the core is made of coated paper or perforated plastic, which allows water vapor to pass, but keeps odors out.

Is an ERV or HRV right for you? While they do essentially the same thing, HRV’s are used in predominantly cooler climates and ERV’s are used in predominately warmer climates (an HRV only manages energy while an ERV also deals with moisture). It would be easy to decide which is best for you if the country was simply divided into the northern part and the southern part. However, the U.S. has eight climate zones. It is best to enlist the services of a qualified Heating, Ventilation, and Air Conditioning (HVAC) expert when deciding which one and what size is best for your situation.

Modular Exceeds Expectations

It’s not just about meeting minimum expectations. It’s about providing a home that is comfortable, safe, and healthy. Indoor air quality starts with the construction of the home. It means keeping lumber dry. It means eliminating dust and construction contaminants from the delivered home. It means using products that are free of Volatile Organic Compounds.

Modular construction helps you create a tight thermal envelope, where you define the line. Now you can ensure that incoming air is filtered (Healthy). You eliminate drafts (Comfortable). You control moisture and humidity (Safe). Building a home using modular construction means you are getting a home that you and your family will enjoy living in for years to come!

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