How Well Does Your Home’s Insulation… Insulate?

Spray Foam Insulation

Unless your home is a barn, it's probably got insulation in it.

Having adequate insulation is important for keeping heat inside during the winter and outside during the summer. It helps us stay comfortable and keeps our HVAC systems from working too hard.

The thing is, your insulation might not be insulating you all that well.

Home renovations, sloppy installation, lax pre-2000s building codes - a variety of factors can impact the performance of your insulation. And since most insulation lives in our attics, crawl spaces, and walls, any problems with it are very "out of sight, out of mind." All you know is that it's hard to stay comfortable during temperature extremes and your utility bills are always high.

What you should do about those problems depends on you, your home, and your insulation situation. That being said, knowing a bit more about what insulation does (and what it doesn't do) can help you determine whether it's time to make changes.

What insulation is and what it isn't

Traditional fiberglass or cellulose insulation creates a thermal barrier. As such, it keeps heat inside or outside your home's building envelope. Its purpose is to inhibit the movement of heat - that's it.

It is not an air barrier. Air can still pass through fiberglass and cellulose, and air contains heat. Therefore, the more air that passes through your insulation, the more heat your insulation has to block. When that air is significantly hotter than the air on the other side of the insulation - like indoor air during winter or outdoor air during summer - it's harder for your insulation to keep the heat in (or out).

Here's one way to think of it. Let's say you're insulating a small shed. On one side of the shed, there's a large hole leading to the outdoors. Instead of nailing a board over the hole, you just shove a fiberglass batt against it. Done, right? Well, not quite.

Every time you run a space heater inside the shed, it seems like it never shuts off. The reason is that the warm air created by the heater quickly escapes through the hole in the wall - it hardly matters that the insulation is there.

Here's the lesson: To optimize the effectiveness of your thermal barrier (insulation), you should optimize your air barrier, too.

But what's an air barrier?

Air sealing: the common missing link between insulation and comfort

As we've written before, warm air moves from the bottom of a structure to the top or, in the summertime, from the top of a structure to the bottom. Respectively, we know these phenomena as the stack effect and reverse stack effect.

In the context of insulation, it means you should prioritize the areas above your ceiling (attic insulation) and below your floor (crawl space insulation). After that, go for the walls. If most homes already have these things covered, which they do, where's the issue?

Enter air sealing. Most homes do have insulation in the attic, crawl space, and walls, but they rarely contain barriers that prevent warm air from penetrating gaps and cracks around:

  • Ductwork
  • Plumbing
  • Wires and cables
  • Bath fans
  • Lighting and ceiling fans
  • Attic hatch doors
  • Electrical outlets

Those might seem like small gaps and cracks. Individually, they are. Cumulatively, however, they can amount to leaving a window open all year round! This is known as "air leakage," and preventing it is key to improving comfort, lowering your energy bills, and getting the most from your insulation.

Older homes usually have poor insulation and no air sealing. Here's how to fix that:

Ok, pre-2000s homes aren't necessarily "old." A two-story, masonite-clad home built in 1980 isn't all that old when you compare it to a brick ranch from the 60s or a 1920s bungalow. That being said, home construction in years past almost never prioritized air sealing the envelope.

Typical insulation R-values also used to be much lower than they are now. Your insulation's R-value refers to the level of thermal resistance it provides. The higher the R-value, the more effective the insulation. The R-value of insulation in newer homes is often more than twice what you find in older ones!

Nowadays, best practices for properly air sealing and insulating your home's building envelope include:

  • Sealing all attic and crawl space penetrations with foam: You need to do this before adding insulation. In existing homes, you can remove the attic and crawl space insulation temporarily, air seal the gaps, and then replace the insulation.
  • Insisting on an R-value around 40: After air sealing in the attic and the crawl space, you can put the old insulation back and blow additional insulation on top of it. Your goal should be to insulate up to an R-value around 40. After that, adding more insulation results in diminishing returns.
  • Choosing blown-in insulation instead of batts: Batt insulation is significantly error-prone. For one thing, it's hard to install properly. You have to cut it to fit a space perfectly; otherwise, you end up with gaps where heat can move freely! Batts also move from their position when you do things like install recessed lighting or add a ceiling fan to a room.
  • Performing blower door-guided air sealing: In older homes, this is a great way to identify areas where lots of air is escaping. Besides the bigger air leaks in your floor and ceiling, the blower door test usually uncovers other sources of leakage: gaps around windows, doors, electrical outlets, and bathroom plumbing are common culprits.

Other, less common, fixes include upgrading your wall insulation and replacing ducts inside the building envelope. Compared to the above upgrades, these changes are usually more expensive and don't result in the same energy savings and comfort improvements.

Upgrading your wall insulation to lower your energy bill is kind of like replacing old windows because you're worried they're not energy efficient. The savings you reap probably won't justify the expense you incur.

What about spray foam insulation?

We're glad you asked! Spray foam insulation is an all-in-one thermal and air barrier. You don't have to do any extra air sealing because the spray foam fits into all the gaps and cracks and blocks air movement.

Spray foam insulation comes in two varieties: closed cell and open cell. Both are great. Closed-cell spray foam is impermeable to both air and moisture, making it a great choice for crawl space encapsulation projects. It also has an R-value of around 6.5 per inch. Open-cell spray foam is not impermeable to moisture, but it's also less costly. It gives you an R-value of about 3.6 per inch. To increase the R-value, just spray on a thicker layer.

In your attic, you apply spray foam to the ceiling instead of the floor. In your crawl space, you can apply it to the walls. When you do this, you're extending the envelope of your home to include the area enclosed by the spray foam.

Here's when it's a good idea to use spray foam insulation instead of fiberglass or cellulose:

  • Your air handler and ductwork are in your attic: When you have HVAC equipment in your attic, it's subject to temperature extremes that make it operate less efficiently. By applying spray foam and bringing your air handler and ductwork into the building envelope, you can prevent your ducts from getting really hot or really cold and extend the life of your equipment. For attics, we recommend open-cell spray foam specifically because it doesn't stop moisture. When there's a leak in your roof, you'll know about it and be in a position to fix it.
  • You're finishing your attic: If you're transforming your attic into a usable space, spray foam is the way to go! Compared to adding batt insulation to your attic ceiling, it's easier to apply and far more effective.
  • You're encapsulating your crawl space: Using closed-cell spray foam on the crawl space walls is a great way to stop air movement and keep moisture from getting in. For this project, closed-cell spray foam is a better option because it helps keep the crawl space dry.

Traditional fiberglass and cellulose insulation still do a great job, but spray foam really comes in handy for projects like these. If your air handler is in your crawl space and you don't plan on finishing your attic any time soon, blowing fiberglass into the attic will work just fine. On the other hand, if you've got a lot of humidity in the crawl space and your fiberglass insulation is falling down, spray foaming the walls as part of an encapsulation project will help you immensely.

It all depends on your goals, your budget, and the problems you're trying to solve.

Air seal + Insulate = Be more comfortable

Whatever route you choose, that's the best order of operations. Air seal first; then insulate. Otherwise, it will be hard to make your home more comfortable.

And while comfort is important, here's something else to keep in mind: The more effectively we insulate, the less energy we use. That yellow stuff in your attic isn't just there to keep you from freezing in the winter. It also helps you pad your pockets and reduces your environmental footprint.

There's a lot to love about that yellow stuff. Comfort is only part of the equation.

Image Credit: dunktanktechnician