Benefits of Insulation
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Building Science
Estimating Costs
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Benefits of Insulation
Find the Right Contractor
Building Science
Estimating Costs
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The building science of insulation and air sealing

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The building science of insulation and air sealing

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Insulation and air sealing work best together

For the best energy savings, it's common for a building to have both insulation and air sealing needs. Insulation and air sealing address different problems, but when done right, they work together to keep your home at a consistent temperature.

illustration showing that air sealing keeps conditioned air in your home and unhealthy air out

Air sealing closes gaps in your home's envelope. This prevents conditioned air from escaping and unhealthy air from entering.

You can think of air sealing as the zipper and shell of a jacket. When zipped, it will block wind, but it won't regulate any temperatures.

illustration showing that insulation acts like the down material of a jacket to regulate temperatures

Insulation slows the transfer of heat between the inside and outside of your house. This keeps your home at a consistent temperature.

You can think of insulation as the filling to a down jacket. Without it, the jacket will block wind, but it won't keep you warm.

What parts of my house are typically air sealed?

The areas of a home most prone to air leaks are the focus of air sealing.

1. Attics

The most critical area is the top plate to attic drywall. Recessed can lights, holes for wiring, plumbing vents, and sealing the access point to the attic are also important to consider.

2. Basements and crawl spaces

Rim joists where the top of the basement wall meet the frame, as well as the foundation, are prone to air leaks.

3. Walls and ceilings

Cutouts for pipes and plumbing, as well as electrical boxes, should be looked at. Additionally, band joists above the foundation wall can be prone to leaks.

4. Windows and doors

Weatherstripping and caulk around entry doors and windows can prevent air leaks and drafts.

What insulation is best?

Trick question – it depends!

Choosing the best insulation for your home depends on the climate you live in, the type of home you have, its size, and other considerations you have beyond temperature regulation, such as fireproofing and soundproofing.

You'll want to consider its cost, longevity, and effectiveness. You'll also want to consider the ideal R-value for your home and region (R-value measures how well insulation resists heat flow. The higher the R-value, the more it resists the transfer of heat).

Energy Star illustration shows recommended R-value insulation levels depending on the region

Common types include:

  • Loose fill – This is blown or sprayed in, so its good for hard-to-reach areas. It doesn't insulate as well as foam, but it's environmentally-friendly and more affordable than other options.
  • Spray foam – This is a liquid latex that hardens into wall cavities as it is sprayed. There are two types – open cell and closed cell – which achieve different R-values.
  • Foam board – This is one of the most common types of insulation. It is expensive, but it has a high R-value, so it is great at resisting the flow of heat, especially in colder climates. Foam board can be used almost anywhere in a home, including the attic, walls, and foundation.

An insulation expert can evaluate your home's needs and discuss your preferences to pick the best type of insulation for you.

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Pros and cons of common insulation types

Loose fill insulation being blown into an attic

Loose fill

Pros:

  • Middle-of-the-road cost
  • Easy to add to nooks and crannies
  • Eco-friendly – made from recycled materials

Cons:

  • Less effective against air leaks
  • Requires a larger space to install with access
Spray foam insulation being installed

Spray foam

Pros:

  • Long-lasting effectiveness – R-value doesn’t degrade over time
  • Fully resistant to mold and mildew
  • Airtight – it is one of the least susceptible insulation materials to airflow

Cons:

  • Requires expertise and specialized equipment to install
Rigid foam board insulation installed in attic

Foam board

Pros:

  • Resists air leaks
  • Resists moisture problems by creating a vapor barrier
  • Reduces noise – effective at absorbing sound waves

Cons:

  • Brittle, which can create air gaps if not properly installed
  • More expensive than traditional batt
The amount of insulation your home needs depends partially on the climate zone you live in

How much insulation do you need?

Another trick question – it depends!

The amount of insulation you need depends on a number of factors, including the climate where you live and your home's age.

Colder climates need insulation with higher R-values, meaning it better resists the transfer of heat, while warmer climates need insulation with lower R-values.

Older homes tend to need more insulation than newer homes, especially if your home is over 10 years old.

Insulation experts in your area will have the best understanding of how much insulation your home needs.

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