Does Spray Foam Insulation Make A House Too Airtight?

If you're considering an insulation upgrade, you may be concerned about the air-sealing of spray foam insulation. Can spray foam make a home too airtight? Doesn't your house need to breathe?

The truth is, you can make a house as airtight as possible as long as you install the proper mechanical ventilation systems. These HVAC systems ensure airtight homes are both comfortable and net a lower total energy usage.

South Central Services began in commercial refrigeration and HVAC, installing over a thousand systems. Since our founding, we have performed hundreds of spray foam installations around Greencastle, PA and in surrounding states. We are committed to growing our expertise in the relationship between climate control and insulation.

Today, we will examine the science behind ventilation and sealing a house. By the end of this article, you will understand:

• The differences between infiltration, natural ventilation, and mechanical ventilation
• What it means for a building to be air-sealed
• Problems air-sealed houses experience without proper ventilation
• How to test a house for airtightness
• How to improve ventilation in an air-sealed house

What Is Ventilation?

Ventilation is how air exchanges from inside and outside a building. Ventilation can occur in three ways: infiltration, natural ventilation, and mechanical ventilation.

Infiltration is when air flows through gaps in a building envelope. Air can pass through an unsealed place in a home. Cracks can exist in the original building design, like gaps in exterior wall framing. Air can also infiltrate through areas that can be difficult to insulate, like electrical outlets, pipes, recessed lighting, and chimneys.

Natural ventilation occurs when we open a window or door. Air naturally ventilates while the door or window is open. We don't control the air or its movement. It just passes through on its own terms.

Mechanical ventilation is when machines, ducts, and fans control air change. An example of mechanical ventilation is turning on the range hood while cooking. The hot air from the stove is directed out of the home so it can be replaced by fresh air filtered from outside.

What Is Air-Sealing?

Air-sealing prevents uncontrolled air infiltration. It seals all the crevices where air would have passed through organically.

Air-sealing doesn't prevent you from opening a window or turning on a fan. Instead, it closes all the little "windows" in your home you can't control.

The fresh air that leaks into your home through uncontrolled infiltration could have allergens, dust, humidity, or temperature differences.

Spray foam insulation is an air barrier that helps seal a house from air leaks. Other air-sealing can include caulking, weatherstrips, energy-efficient windows, and insulation around electrical outlets and recessed lighting.

Can Air-Sealing Cause Ventilation Issues?

Air-sealing aims not to prevent air exchange but to control the air quality. Air-sealed homes need appropriate support from mechanical ventilation for optimal safety and comfort. If there are ventilation issues in an air-sealed home, the solution lies with the ventilation systems.

These systems could include an appropriately sized HVAC, a heat recovery ventilator (HRV), or an energy recovery ventilator (ERV).

Problems Ventilation Issues Can Cause

A lack of ventilation can cause numerous problems in a home. Here are a few issues that would be especially prevalent in an air-sealed home with poor ventilation.

1. Unpleasant Odors

You have probably seen a laundry detergent commercial involving a mother walking into her teenage son's room and nearly passing out from the stench. Those commercials may be dramatized, but the principle applies.

Smelly air might come from trash cans, appliances, dirty laundry, furniture, or other sources. If a home is air-sealed and lacks proper ventilation, that air is trapped. Without proper ventilation, these odors will stay in the home. The smelly air cannot escape the home or be exchanged with fresh air.

2. Poor Air Quality

Living in a home will produce indoor air pollution. Using a fireplace can release smoke and ash. Cleaning the bathroom with cleaning products can introduce gases into the air. Particulates like dust can build up over time. Any of these pollutants can cause itchiness in the eyes, headaches, and irritation when you breathe.

In an air-sealed home, mechanical ventilation is necessary to remove stale or dirty air and replace it with filtered fresh air. The standard HVAC system in a home is more concerned with comfort than air quality. Additional HVAC equipment may need to be installed to improve air quality and ventilation.

3. Humidity Issues

There is always some level of moisture in the air. The humidity can increase quickly by showering or cooking something on the stove. Imagine boiling a pot of water and not removing the steam with a fan. After showering, what if all the condensation on your bathroom mirror has nowhere to go?

Mechanical ventilation systems process that air appropriately in an air-sealed house. Otherwise, excess moisture in the air can cause mold, mildew, window condensation, and paint peeling.

How To Measure Airtightness And Ventilation

If an air-sealed home is airtight, appropriate mechanical ventilation must be provided. But how do we measure airtightness?

Blower door tests measure the tightness of a house. Professional technicians who perform blower door tests use an instrument that creates a vacuum effect on your house. The tech takes measurements of your home to determine the overall cubic feet within the living area. Then, a fan sucks air out of the house, and the professional can see how many air exchanges are leaking through exterior walls, floors, and ceilings.

Technicians can also pinpoint air leakage areas during the test using a thermal camera.

At the end of a blower door test, you will receive a score that shows the overall air exchanges per hour of your home.

Air changes per hour (ACH) can represent ventilation. ACH measures how much air in your home exchanges with outside air every hour. A low ACH is a result of minimum air leakage and may indicate a need for mechanical ventilation in the building.

How To Improve Mechanical Ventilation In An Air-Sealed House

If testing reveals that your air-sealed home does not have appropriate ventilation, contact an HVAC professional familiar with air-sealing. A HVAC contractor can determine what measures need to be taken, including:

• Ensuring the system(s) are working at their full potential and are sized appropriately.
• Resizing the HVAC system to better support the air-sealing insulation.
• Cleaning exhaust fans, including bathroom, kitchen, and dryer vents.
• Recommending and installing an HRV or ERV.

A House Cannot Be Too Airtight

The good news is that an airtight home doesn't need an insulation change, but an HVAC companion to support its insulation and air-sealing. We can be more comfortable and live more efficiently in our homes by controlling air changes and optimizing mechanical ventilation. No matter how airtight a home is made, necessary ventilation is still possible through natural and mechanical means.

Now that you understand why houses cannot be too airtight, your next step is to:

• Learn more about the importance of air-sealing
• Discover the products used to create an airtight seal
• Find out if a house can be over-insulated