Air Sealing – Stop Heating or Cooling the Outdoors




The benefits of air sealing (or weatherization) and insulation trickle down to almost everything else you decide to do to upgrade your home.

This energy measure is one that can easily be undertaken by you for the most part, but special cautions must be taken when dealing with anything that has electricity, gas, or fire (chimneys and flues) attached to it.

The most common culprits of air leakage are:

  • Openings and cracks where two walls meet, where the wall meets the ceiling, or near interior door frames;
  • Gaps behind recessed cabinets, and false ceilings such as kitchen or bathroom soffits;
  • Attic entrance;
  • Behind bath tubs and shower stall units;
  • Through floor cavities of finished attics adjacent to unconditioned attic spaces;
  • Utiltity chases for ducts, etc.,
  • Gaps around electrical outlets, switch boxes, and recessed fixtures;
  • Plumbing and electrical wiring penetrations.


Air Sealing Notes and Tips – Understand these and you’re golden

  • DO NOT rely on air leakage for ventilation. During cold or windy weather, too much air may enter the house and, during warm or calm weather, too little.

    Also, a leaky house that allows moldy, dusty crawlspace or attic air to enter is not healthy.

  • You can locate air leaks by holding a lit incense stick or even a sheet of plastic wrap taped to a pencil close to these areas, and watch out for horizontal movement by the smoke or the wrap.
  • Prioritize by sealing all the big holes first, then the large cracks and penetrations, and finally the smaller cracks and seams.
  • Ironically, the biggest holes are usually hidden from view and connect the house to the attic, crawlspace, or basement, not windows and doors.
  • The exterior shell of your house (wood under siding, etc.) is constructed from different material than the interior shell of your home (sheetrock/drywall, plaster, sheating, etc.).

    There is an air gap between these 2 materials which if sealed properly, causes an air barrier (similar to an entry way air lock). SO, make sure to seal all holes and seams between these sheet goods with durable caulks, gaskets, and foam sealants.

    That being said, remember that fiberglass insulation, does NOT stop air leakage. If you have an older homes, look for dirty fiberglass as a telltale sign of air leakage (it collects dirt like a filter).

    Certain types of insulation, such as dense-packed cellulose and certain foams, can be effective at reducing air flow as well as heat flow, but again, know where the leaks are and who is fixing it.

Types of Air-sealing Products

If you decide to go the professional route, energy auditors and building professionals use a diagnostic tool for checking the air tightness of a building called a blower door can help to ensure that air sealing work is effective. Otherwise, you can use the methods above to identify leaks use a combination of these products for air sealing solutions:

  • Caulk - Seals gaps of less than ½" and comes in interior, exterior, high temperature grades.
  • Spray foam - very effective in Filling large cracks and small holes but it can be messy; you might want to consider latex-based foams. DO NOT USE near flammable applications (e.g., flue vents). DO NOT USE expanding types on windows and doors.
  • Weatherstripping - Used to seal moveable components, such as doors, windows, and attic accesses.
  • Gaskets - Apply under the bottom plate before an exterior wall is raised or use to seal drywall to framing instead of caulk or adhesive.
  • Backer rod - Closed-cell foam or rope caulk. Press into crack or gap with screwdriver or putty knife. Often used with caulk Use backer rod to fill gaps between window and rough opening before caulking or use non-expanding foam.
  • Housewrap - Installed over exterior sheathing. Must be sealed with housewrap tape or caulk to form an airtight seal. Resists water but is not a vapor barrier.
  • Sheet products (such as plywood, drywall, rigid foam insulation) - These materials form the air barrier. Air leaks only at unsealed seams or penetrations.
  • Sheet metal - Used with high-temperature caulk for sealing high-temperature components, such as flues and chimneys, to framing.
  • Polyethylene plastic - This inexpensive material similar to food wrap is great for air sealing and stopping vapor diffusion. Poly is fragile, and all edges and penetrations must be completely sealed. This is a good strategy for winterizing windows.
  • Mastic - Seals air handlers and all duct connections and joints.
  • foil-faced tape (UL181)- Temporarily seals an air handler.



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