Air Sealing the Exterior of Your Home: Preventing Mold & Increased Moisture Levels

Man on ladder caulking outside window
Man on ladder caulking a window

If you live in a hot-humid climate, poor air sealing on the exterior walls and windows of your home contributes to internal mold growth and elevated moisture/humidity levels.

Poor air sealing also has a negative impact on the durability of your cooling system, as it will need to work harder to cool and dehumidify your home.

Taking a few hours out of your day to seal around windows, doors, & exterior penetrations can have a significant impact on your home, and every little bit helps.

In the article below, I’m going to provide for you:

  1. A list of locations that likely need to be sealed
  2. Links to how-to articles I’ve read and approved
  3. Basic tools that I use/own and recommend for the job

Sealing Windows and Doors

A major source of air infiltration can be found around your windows and doors. The most egregious defect for either component is damaged or missing weather-stripping. Without weather-stripping, moisture-laden unconditioned air will be pulled into the home (mechanical air systems pressurize the enclosure). Before you break out the dripless caulk gun, you should remedy these larger air leaks.

A secondary source of air infiltration is around the glass panes within doors and windows. Both of those locations will need to be adequately caulked if you notice that the previous caulking is deteriorated or missing. In addition to preventing air-infiltration, you’ll also have help to prevent water infiltration.

The most common location that I find wind-driven rain entry on windows is at the transition between the glass pane and lower sash. Even more, I find that fixed windows leak more than operable windows at these locations. It makes sense because fixed windows generally have a larger surface area with no obstructions (rails, muntins, sashes).

Bonus Tip: If you need a ladder, I use this one, and it’s far and away the best ladder I’ve ever owned. 

Sealing all Wall Penetrations

It is also beneficial to seal all penetrations that protrude out the exterior wall. In theory, each of those penetrations should have been appropriately sealed/flashed during the framing phase of the home, but a lot of builders fail to properly flash and seal the air and water-resistive barrier before constructing the exterior wall.

I recommend checking and sealing the following locations:

Electrical Distribution: Main panel, electrical meter, outlets, light fixtures, disconnects

Plumbing Distribution: Water faucets, Shut-off valves, clean-out caps

Mechanical Systems: HVAC refrigerant lines, fireplace fresh-air intakes, through wall exhaust vents

Additional Benefits of Air Sealing Your Home

Another reason to seal exterior penetrations is to prevent rainwater from gaining access to any of the electrical connections. Over time, the exposure to moisture can weaken electrical bonds and increase the wear on components, which are both negatives for electrical safety.

Finally, a simple reason to seal these areas is aesthetics. When you eliminate gaps and openings in the exterior wall system, the overall appearance is improved. Couple that with color matching, or paintable sealant and you can further enhance the look of your home.

If you are looking for additional information on what type’s of sealants should be used, Fine Homebuilding article sums up the particulars on caulks and sealants quite nicely.

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