Increase Your Ankeny Home Energy Efficiency: Sealing Air Leaks


The attic is the leading source of air leakage in homes. To make your home more comfortable and increase its energy efficiency, seal and insulate your attic. By locating and sealing air leaks throughout your home, particularly in the attic, you could see a noticeable difference in your monthly energy bills and you’ll help protect the environment, as well.

Since warm air rises, it is very important that your attic is sealed tightly and properly insulated. You don’t want your home's heat to escape through the attic. Aside from high energy bills, this can cause several other serious issues. If you have a poorly insulated attic with several air leaks, you have probably experienced one or more of the following problems:

  • Drafts throughout the home
  • Uneven temperatures from room to room
  • High energy bills
  • Ice dams
  • Dust
  • Dry indoor air
  • Condensation issues
  • Water damage

Locating Air Leaks

While you may have issues with drafty windows and doors, the source of wasted energy that has the most significant impact on energy bills is the attic. Cold air often comes into homes through drafty windows and doors and through the basement. If the attic is not sealed properly, the heat you are paying for during the winter can rise up to the top of your home, into the attic, and escape out of the roof, leaving your home drafty, uncomfortable, and inefficient.

It can be difficult to find air leaks in the attic if they are located underneath insulation. You may be thinking, “as long as I have good insulation, I don’t need to seal the air leaks.” Sealing leaks, however, allows the insulation to work more effectively. When looking in your attic for signs of air leaks, look for dirty insulation. This is a sign that air is passing through it.

Be aware, however, that it may not be safe for you to climb up into your attic. If you have vermiculite insulation, for example, it may contain asbestos, which is very harmful for you to touch and breathe. It will need to be tested by professionals and approved for safety before it is disturbed.

Knowing which areas of your roof are most vulnerable to air leaks will help you determine where to look. Before going up into the attic to locate and seal the leaks, get your bearings from below. It will be very helpful to first make a quick sketch of the layout of your floor plan. Mark the locations of any dropped soffits, slanted ceilings (over stairs), furnace flue, chimney, main plumbing stack, and where walls meet ceilings. These areas could have open stud cavities that lead directly into the attic, where a huge amount of air may be leaking. You might also make note of anything else that penetrates the ceiling (pipes, lights, electrical wiring, the attic hatch, ducts, electrical outlets, etc.). Many of these will be difficult to locate when you're up in the attic since they will likely be hidden under insulation, so a sketch of the layout will prove very useful.

Once you’re up in the attic space, reference your sketches to locate possible problem areas. Search for the big holes to seal off first. Fixing these will result in the most significant improvements in efficiency. The next step in the process will be sealing any air leaks you find, which we will walk through in our next post.

Check your attic and your insulation for signs of moisture. If you notice that your insulation is damp or you have mold or rotting wood in your attic, you have a moisture problem. If this is the case, call a professional roofing contractor to fix these problems for you before you move on to sealing air leaks yourself. Other reasons you should call in the pros include:

  • Frequent ice dams in winter
  • Moist air vented into the attic space instead of outdoors
  • Poor attic ventilation
  • Unsealed and uninsulated recessed lighting

Sealing Air Leaks 

Open Stud Cavities


To seal open stud cavities, cut a 16-inch piece of fiberglass (batt) insulation, and stuff it into a 13-gallon garbage bag. Then fold the bag (and insulation) in half, and push it into the open stud cavity. Check to make sure it's a tight fit. If not, add more insulation to the bag and try again. Re-cover the area with insulation when you're finished.


Knee Walls 

Attics often have open cavities in the floor framing under the knee walls. To seal air leaks in these spaces, grab your fiberglass insulation and garbage bags again. Cut a 24-inch piece of insulation and stick it inside the bag. Fold and shove it into the open joist spaces underneath the wall, and then cover the area with insulation again.


Furnace Flues, Chimneys, and Water Heater Flues 

A lot of air can leak around structures that penetrate the attic floor and the roof if they aren’t sealed and insulated properly. These structures can be very hot, so be careful! Building codes require a certain amount of clearance around these types of structures, so make sure to check each item's clearance requirements before sealing around it. If you are unsure of how to proceed, ask a professional to help you.

Once you understand how much clearance is required around your structure, it’s time to seal the leak. You’ll need to build a metal dam around the structure to keep the insulation far enough away from the pipe, based on how much clearance is required. You can then use lightweight aluminum flashing and high-temperature/heat-resistant caulk to seal the area.


Dropped Soffits

First, remove any insulation from the area. Next, cut a piece of reflective foil insulation or rigid foam board a few inches larger than the size of the space you need to seal. Place a bead of adhesive (such as caulk) around the opening, and lay the foil down on top to seal. You may need to nail it down to make sure it stays in place. Re-cover with insulation.



Search for dirty insulation. Lift it up, seal the leaks with expanding foam or caulk, and then place the insulation back down on top once the area is dry.


Pipes and Wiring 

Fill small holes around wiring and plumbing with expanding foam. If gaps around pipes are larger than 3 inches, first stuff the space with some fiberglass insulation, and then add expanding foam to seal the smaller holes around the insulation.


Attic Hatch 

To seal the space around your attic hatch or door, add self-sticking weatherstripping.

Make sure to read all directions carefully and abide by any safety measures listed on instructions for all sealing and insulating products. Don't attempt any work you are uncomfortable with or are unsure of how to handle on your own. It's always better to be safe and have a professional do the work for you than to take an unnecessary risk that could end badly. If you are going to seal up your home, make sure that you have a proper ventilation system in place. Contact your local heating and cooling company to check on your combustion appliances to ensure they are venting properly to the outdoors and not into your home, which can lead to carbon monoxide buildup.


If you would like help locating or sealing air leaks in your attic or you're looking for roofing and insulation services, Hedrick Construction is here to help! Our professional roofing contractors will work with you to make your home more comfortable and energy efficient, providing protection for both your family and the environment.

Get a Free Estimate