Seal Attic Air Leaks

By Robert Robillard on Energy Saving

Seal Attic Air Leaks and Save Money on Heating Bills

Attic heat loss due to air leakage accounts for one-quarter to one-third of your annual heating bill!

Insulation itself does not stop the air leaks – you need to stop air leaks in order to let the insulation do its job.

TIP:  Blackened insulation is always a good clue that air is leaking in the area.

For less than $100 in caulk, foam and other materials available at hardware store or home center, plus a day’s labor, you can seal attic air leaks by plugging thee holes causing the air leaks and significantly reduce your heating bill.

Plug open stud and joist cavities

Your biggest savings will come from plugging these big holes first.

Open stud cavities are the worst [located in lowered areas of ceilings (sofits) and where the ceiling height shifts, especially in split-level homes.] Plug them with a plastic bag partially filled with insulation. The plastic bag stops the airflow. The insulation makes the bag expand tightly to close off gaps. You can also use tightly fitted rigid foam board or sheet plastic to cover these openings or expanding foam.

Doors and pull down stair hatches

Openings like doors and stairway hatches tend to be the biggest UNINSULATED hole into the attic and air leak culprit.

Weather strip the edges and insulate the backside of the attic door or stairs. Fold-down stairs can be covered with a lightweight box made of rigid insulation board.

There are commercially available attic stair insulator caps that can be purchased [pictured below]. They range from $60 to $200. See here for an example. of a commercial version.




To make your own attic stair insulation box like the one pictured below, click here.

Find holes in the floor of the attic

Floor holes, especially around the outside walls, ducts, recessed lights or near plumbing utilities. Also, look for dirty spots in your insulation, this indicates holes where air is leaking into and out of your house. You can seal these holes by using foam sealant, or stapling sheets of plastic over the holes .


Around the chimney

Any chimney that runs from the basement through the attic should be sealed at both the basement ceiling and attic floor by use of sheet metal or metal duct tape. Fire codes prohibit the use of combustible materials within 2 inches of chimneys.

NOTE:  Fiberglass is not an effective air barrier. You can use rock wool in the cavity to insulate but you still must stop the air leakage with a non combustible material. I recommend using metal roofing drip edge, screwed to the floor joists and caulked with fireproofing caulking.


Around the sewer vent pipe

A sewer vent pipe typically runs vertically from the basement through the attic and should be sealed at both the basement ceiling and attic floor by use of wood, sheet metal, or metal duct tape and caulked with fire proof caulking.
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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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