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When building scientist John Costello was teaching courses on home performance and sustainability, he often spoke to the importance of air sealing, especially in a home’s attic. There, said Costello, small holes in recessed lights and outlet plates drew in enough air to significantly impact the air quality in the rest of the building.

And while he knew his students paid attention during class, he didn’t know just how much of a difference his words made.

“By the end of one of my classes,” says Costello, “a student approached me with tears in his eyes, explaining that his 4-year-old daughter had been sick and the doctors could not determine the cause.”

While attending John’s class and learning about how air leakages could lead to poor air quality, his student recalled installing recessed lighting in his daughter’s playroom, which was right below the attic — where pigeons also happened to be living at the time.

“After a deep gasp, I told my student to remove any contaminated insulation, air-seal the attic floor, and build airtight boxes around the lights,” John says.

A few months later, John received an update from his student, saying after following his explicit instructions, his daughter was now healthy and just celebrated her fifth birthday.

When considering any home upgrades, your building shell should be top of mind. It’s one of those investments that reaps multiple benefits. Air sealing, for example, may improve energy efficiency, but it can also have health benefits, increase your family’s comfort, and make your home more resilient against whatever the outside world throws at it.

Let’s look at how else your building shell works hard for your family — and how you can keep it in good working order year after year.

What Is a Building Shell?

If you’re a homeowner, you may have heard the term before, but just in case, your “building shell” is the structural skeleton of the home, including its foundation and external walls. What you may not have heard about is how the shell of your home can impact energy costs, indoor air quality, resilience to extreme weather, as well as its resale value.

Related Post: 5 Ways to Upgrade Your Home and Its Appraisal Value

Before installing insulation, the most important action to take is air sealing, says John Costello, Pearl Certification’s building scientist. He says no matter how big or small an air leak is, the impact can be tremendous when it comes to maximizing your home’s efficiency and your health.

Building Shell Components

Attic & Roof

Ensuring you have a leak-free attic and roof is critical to the efficiency and safety of your home. Without a strong roof, the rest of your home is at risk of being damaged.

“Oftentimes, attics and roofs are the first components to be addressed in home retrofits and can be considered the most important because of the location,” says Costello. “Roof leaks can also lead to moisture damage throughout the home,” he says, “and air leaks can allow warm or cool air to escape, causing your home to be much less efficient.”

It’s estimated that approximately 25% of your home’s heat can escape through the roof, making it much more expensive to heat or cool if air is escaping. Ensuring you have proper roof and attic insulation and air sealing is paramount. If, however, you’re in the market for an entirely new roof and you’re in a warm climate, cool roof designs can offer improved efficiency. These are designed to reflect more sunlight than conventional roofs, thereby lowering the temperature of your home and requiring less cooling during hot summers.

Related Post: The Ins and Outs of Insulation


It’s a common misconception that only hot air rises. In fact, heat always moves from hot to cold, so if it’s cold outside and hot inside, your home can lose a lot of heat just through the walls. It’s estimated that walls account for 35% of home heat loss, so making sure you have proper wall insulation and that any gaps around pipes or outlets on exterior walls are sealed tightly is critical for maximizing efficiency.

Floors and Foundations

The floors, foundation, and basement or crawl space of your home are just as important to maintain as the attic and roof. From a safety and resilience perspective, without a solid foundation and flooring, the rest of your home is at risk of being damaged, especially if you live in an earthquake-prone region.

But beyond just ensuring your foundation remains damage free, it’s important that you properly insulate and seal your floors. Insulating your floors is one of the best ways to increase the return on your investment. Improperly insulated or sealed floors can lead to an estimated heat loss of 10% and can also lead to moisture damage. In addition to reducing heat loss, insulating and air sealing your floors can also improve soundproofing, lower your utility bills, and provide greater comfort through improved temperature control.

Rim Joists

Rim joists are especially important for two-story homes and are defined as the areas where your home's floor framing meets the outdoors. Rim joists require air sealing and insulation, just like your home's walls. It’s one of the easiest ways to improve your home’s energy efficiency, prevent water damage, and ensure small insects and pests don’t make a home in your home.

“Rim joists are often overlooked as they often don’t have large spaces to fill with insulation,” says Costello, “but they can be insulated and air sealed on their surfaces by using materials like foam board, batts, and spray foam.”

Windows and Skylights

One of the top energy-efficient retrofits involves replacing windows and skylights with energy-efficient models. Special coatings and double panes equip high-efficiency windows with better insulation, which in turn helps keep warm air inside your home during the winter and maximizes heating efforts.

If you live in a hurricane-prone region, you can also invest in impact-resistant windows that can withstand high wind speeds. Impact-resistant windows and skylights also improve the durability and safety of your home in the face of increasingly frequent extreme weather events. Windows and skylights that are well insulated eliminate drafts, decrease external noises, and lower monthly utility bills — wins all around.

Related Post: The Climate-Resilient Home: Storm Protection


Like windows and skylights, doors are opportunities for leakages. Most people replace doors with aesthetics in mind while ignoring construction material and resistance to damage. While solid wood doors may be aesthetically pleasing and can offer curbside appeal, they are often the first to experience weather damage or become impacted by moisture, which makes them prone to air leaks. For maximum efficiency, Costello recommends doors made of fiberglass with a foam fill and minimal glass.

Next Step: Create an Investment Plan for Your Building Shell

Now that you have a better idea of the importance of your building shell components, it’s time to think about where and when you may want to make upgrades, based on your goals and budget. Pearl makes it easier to plan and fulfill those goals with our free Green Door app. Use Green Door to generate a customized Home Investment Plan (HIP) based on your home’s age, assets, and location plus your own goals. Identify home performance improvements that will give you the most bang for your buck, and connect with Pearl Network Contractors for Pearl Certified installation — get started on your free plan today!

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