Attic Insulation & Air Sealing: Should You Do Both?

Picture this: it’s a cold winter morning and you’re leaving for work. You just made some coffee and you want it to stay warm for the drive. What do you do? You pour it into a tumbler and seal it with a lid on top. 

This tumbler keeps your coffee warm much the same way attic insulation and air sealing do for your home. 

The stainless steel interior of the tumbler works like proper insulation, helping to keep heat from escaping or entering through the sides of the cup. The rubber sealing of the lid works like your home’s sealing, keeping out cold air while helping keep the warmth inside from seeping out of any gaps. 

Both insulation and sealing work in their own ways to help maintain a regular internal temperature and they’re essential parts of creating optimum energy efficiency. In this article, we’ll go over the different ways attic air sealing and proper attic insulation help stop the flow of heat and which is more important for keeping your home comfortable. 

What is Attic Insulation?

Insulation works by creating a thermal barrier between your home and the outside world. This barrier helps reflect the weather outside your home and maintain the indoor air quality and temperature inside, so you’re heating and cooling systems won’t have to work as hard to keep your home comfortable. 

However, according to Energy Star, 9 out of 10 homes in the U.S. are underinsulated.1 This means most people are likely overpaying for their energy bills due to their home’s inability to properly regulate temperature. 

The good thing is that existing insulation technology has come a long way in the last few decades and there are many insulation options for homeowners. 

Signs Your Home’s Insulation Needs Updating   

If you aren’t sure whether or not your home is properly insulated, here are some warning signs of poor insulation to look out for: 

  • High energy bills 
  • Drafts indoors
  • Temperature fluctuates from room to room
  • Cold interior walls or floors 
  • Visible joists in the attic 

If your home shows any of these signs, it might be time you had your insulation replaced. 

Types of Insulation

Insulation is not a one-size-fits-all kind of business. It comes in a variety of different materials, each of which works to regulate the temperature in your home differently:2

  • Fiberglass batts – Fiberglass batts may look like big rolls of cotton but they’re actually made of tiny pieces of fiberized glass. These fibers are spun into long blankets for easy installation. 
  • Blown-in Fiberglass – Blown-in fiberglass insulation is made up of the same material as batts, except instead of coming in big rolls, they come in small pieces that are blown into place. They’re popular for being one of the most affordable and effective forms of insulation. 
  • Cellulose – When examining Cellulose vs Fiberglass insulation, Cellulose is made of extremely finely shredded pieces of newspaper that have been fiberized to stick together and block heat flow. It’s a cheap and simple-to-install form of insulation, but it doesn’t survive well in humidity or against pests. It is actually a common misconception and marketing strategy to try and position cellulose as a pest retardant. 
  • Spray Foam – Spray foam insulation provides an airtight seal and is completely waterproof. Unfortunately, it does also come with a higher price tag, is typically used for industrial use only, and can be difficult to install without professional assistance. 

What is Attic Sealing?

Even if your home has high-quality insulation, it may not be enough to keep the temperature in your home regulated. In fact, it’s commonly thought that if you add up all the gaps and leaks in the average home’s envelope, it would be the equivalent of leaving a window open all year.3

So how can you tell if your home has a sealing problem?

Oftentimes, the signs of poor attic air sealing are similar to those of poor insulation—drafty rooms, high energy bills, uneven room temperatures—so it can be difficult to tell whether the problem you have is because of bad insulation or sealing. 

To determine the root cause, you may need to do some investigation.

Identifying the Source of Your Air Sealing Problem

Most of your air sealing problems are going to come from the parts in your home where there are natural gaps, such as where walls meet or where pipes disrupt the structure of your home.4 

There are a number of different tests you can do to figure out if you have a gap in one of these areas.

Visual Inspection

The simplest way to find significant gaps in your home’s sealing is by conducting a visual inspection of places where sealing problems commonly occur, including:5 

  • Kneewalls 
  • Soffits
  • Door and window frames
  • Plumping, wiring, and pipes 
  • Chimneys or furnaces
  • Baseboards
  • Switchplates
  • Attic hatch 

If you notice a hole in any of these places, make a note of it and come back later to seal it. 

The Light Test 

If you’re not sure where to look for gaps in your home’s sealing, the light method can be incredibly helpful. Simply turn on light fixtures in a room where you suspect there’s a leak and observe from the outside where the light shines through. Wherever you see the light shining is a place that needs to be sealed. 

The Paper Test  

If you specifically want to see how energy efficient your outside-facing doors and windows are, you can use the paper test. All you need to do is shut your window or door on a piece of paper and then try to pull it out. If the paper comes out all in one piece, the door or window will need to be properly sealed. 

The Smoke Test  

For air leaks that are difficult to locate, you can try a smoke test. Here’s the procedure:

  1. Wait for a day when the outside weather is cool and windy.
  2. Turn off all combustion appliances and block off all exterior-facing windows, doors, and chimneys.
  3. Turn on all exhaust fans that blow air outside.
  4. Light an incense stick or sprinkle talcum powder in the air around the edges of the room. Where you see the smoke or powder moving out of the room, there’s a leak that will need to be sealed up. 

How to Seal Gaps in Your Home’s Envelope

After you identify where the leaks in your home’s sealing are coming from, there are a few steps you can take to mitigate the problems, including: 

  • For large gaps, like those around knee walls and soffits: Using proper protective gear, fill a garbage bag full of fiberglass insulation and stuff it into open cavities until the bags fit tightly. Follow Attic Construction’s guide for a full breakdown on fiberglass insulation cost
  • For heat-sensitive areas, like those around chimneys and water heaters: Seal gaps with lightweight aluminum foil, making sure to leave a metal dam between the area and any potentially flammable insulation.
  • For smaller holes, like those around plumbing and wires: Use an expanding foam or caulk to fill up cavities.

Always make sure you’re performing these insulation fixes safely, using the proper protective gear. If you have any questions, reach out to the experts at Attic Construction.

Attic Insulation vs Air Sealing: Which Is More Important?

Both insulation and sealing work together to regulate the temperature of your home, but which is more important when it comes to keeping energy costs in your home down? 

To answer that question, we’re going to revisit our tumbler analogy from earlier. 

Let’s say you were to take your hot coffee with you to work in a non-insulated container, like a mug or paper cup. Since there’s no insulation to keep the heat of your drink from leaking out the sides, where it is surrounded by winter air, your drink will quickly lose heat and will likely be cold by the time you arrive at work.  

If, on the other hand, you were to bring your drink to work in an insulated tumbler without the lid, your drink will still cool down while you drive but at a much slower rate, so your drink will likely still be warm enough to drink by the time you arrive at the office. 

The reason for this is insulation does a lot more work to regulate temperature than sealing does as it covers more surface area in your home. As long as the gaps in your home aren’t major and clearly visible from the outside, having high-quality insulation is going to be a more essential part of keeping your home’s temperature regulated and your energy bill down. 

Attic Construction: Help with All Your Home Insulation Needs

If your home is in need of insulation services, Attic Construction is here to help. When you sign up for Attic Construction’s free home inspection, one of our expert contractors will come to your home to give a thorough inspection of your home’s insulation situation and give you a detailed understanding of what steps need to be taken to improve it. 

Whether you’re looking for Phoenix insulation installation, rodent proofing in San Diego, or attic cleanup in Orange County, we’re here to get the job done.

Visit our website today and sign up for your free home inspection to find out how you can start saving money on your energy bills and living more comfortably!


  1. Energy Star. Why Seal and Insulate?
  2. Energy Star. Attic Air Sealing Project.
  3. Energy Star. What to Look for: DIY Checks and Inspections. 

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