Home air sealing and insulation: How tight is too tight?

Every home has what’s known as a ‘building envelope’ that protects it from the elements. This envelope is the barrier that separates conditioned spaces (heated and cooled space, such as interior rooms) from unconditioned spaces (unheated and uncooled spaces, like unheated attics and garages). A typical building envelope consists of the roof, walls, windows, and doors of a home. It’s important to strike the right balance with air sealing, insulating and ventilating your home so you can save energy, protect your home and stay comfy.

Problems with a leaky home

Without air sealing and insulation in your home, you could be losing 20 to 30 percent of your heated (or cooled) air through leaks, holes and poorly connected ducts1. Then your furnace and air conditioner have to work harder, because they kick on more often to make up for this loss, driving up your utility costs and overall energy consumption. Air leaks can also contribute to moisture problems, like mold growth and rotting wood in your home. In this way, a leaky building envelope could be bad for your health and your home’s structural integrity.

How tight is too tight?

To prevent air leaks and stay comfortable, homeowners and builders look to create a tight envelope with air sealing and insulation. Insulation must meet minimum acceptable R-value provided by state code laws. An R-value for walls represents the sum of cavity insulation plus any insulated sheathing2. For new construction homes in Illinois, insulation for wood frame walls must have an R-value of 20 to meet minimum requirements. Where insulation is added and how much is used affects how well your home keeps in heat in the winter or cool air in the summer.

But how tight is too tight? Experts say there’s no such thing as a home that’s too tight; it just requires proper ventilation. Without ventilation, pollutants can build up and impact air quality. You can determine how tight your home is with a blower door test. During this test, an auditor sets up a blower door fan to pull air out of the house, allowing outside air to flow in through unsealed cracks and openings. An auditor then uses a tool, like a smoke stick, to find the leak3.

To measure how leaky the home is, the home is depressurized to 50 Pascals and the amount of air that enters the house is measured in cubic feet per minute (CFM). This measurement is often written in shorthand as CFM50. For an average home, between 500 and 1,500 CFM50 is considered “tight.” A home with CFM50 greater than 1,500 may benefit from air sealing.

Making it just right

Don’t settle for a house that’s leaky. See if your home could benefit from improved air sealing and insulation. If you’re thinking about an air sealing and insulation project, use the Find a Contractor tool from energySMART, a Nicor Gas program. This tool will pair you with professionals in your area that are certified by the Building Performance Institute.

By working with an approved contractor, you can qualify for an instant rebate on your project. You can rest easy knowing that your envelope will be up to industry standards, so you can get comfortable and start saving money and energy right away. Have questions about air sealing and insulation projects? Visit our FAQ page or call our team at 877.886.4239.


1https://www.energystar.gov/index.cfm?c=home_improvement.hm_improvement_ducts

2http://insulationinstitute.org/wp-content/uploads/2015/12/IL-2012.pdf

3https://www.energy.gov/energysaver/blower-door-tests

4http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/how-tight-too-tight