Are my windows causing my mold allergy?

If you viewed the results of my home’s mold plate testing, you probably saw the high count of mold colonies in my sunroom–which doesn’t even have air conditioning vents in it.   What the heck?  I was scratching my head until I remembered that I had placed the plate on a table only a few feet away from the exterior wall of windows.  There are 12 exterior windows in that room!

Here are some of the ways that windows can increase mold counts in your home:

• Direct water leaks:  if the seals or caulking fail on your window(s), they could allow water to run into the wall, where mold can grow.

• Drafty windows allow air to pass from the outside in, or inside to outside, where the temperature and humidity difference can surpass the dewpoint and cause condensation.  Condensation can occur on the windowsill or anywhere around the window that is not properly sealed.

• Outdoor mold can grow on the screens, because they retain dust and moisture.  When you open windows, air blowing through the screens will blow mold spores right into the room.

• Heavy window treatments create a micro-climate between the room and the window.  Although they are great at insulating the room from heat or cold, fabric curtains retain humidity/moisture, and also create a cold pocket of air without air circulation.  With drafty windows, air between long curtains and the wall can allow condensation, and offer the ideal darkness for mold to grow.    

In my case, I believe it was the drafty windows that allowed air to blow around the frames and carry mold into the room.

Here are some ways to get that mold count down:

• Check for leaks in your windows.  Here are some warning signs that a window is leaking and how to determine where it is leaking (video):

• Peeling paint on an interior window sill 

• Peeling paint on an interior wall near a window

• Rotting wood on the exterior window frame or sill

If you have any of these symptoms, it’s best to remove the outer siding materials and find out where the water is getting in, because cosmetic repairs will not fix the leak. 

• Decide whether to replace or reseal your windows.  It’s rarely an easy decision because replacing your windows is not likely to save you money, considering the cost of the windows and installation.  However, there are some ways to know that it’s time to replace them:

• Replacement: If your windows are extremely damaged by water infiltration, then it’s a good case for replacement. (ecohome.net)  There are many options for energy-efficient windows, available in wood, vinyl or composite (fiberglass or a combination of materials).  Like many products, the installation of the windows is just as important as the quality of the windows themselves. Quality installation is critical for an airtight fit and a continuous water barrier to prevent drafts, water damage and condensation.(efficientwindows.org)  To select windows, the National Fenestration Rating Council (nfrc.org) is a non-profit organization that gives consumers energy performance ratings and other useful information about windows, doors, and skylights.  You’ll also want to consider that new exterior windows that meet Energy Star standards fall under “qualified energy efficiency improvements” which can generate tax credits.  For windows purchased in 2022, you can claim the Residential Renewable Energy Tax Credit for 30% of the total cost, up to a maximum of $600 for exterior windows and skylights. (filemytaxesonline.org) In addition, check with your local power supplier to see if they have more incentives for replacing windows. If you do decide to replace, remember that higher-cost wood windows (which are clad in aluminum or vinyl for weather protection) are only as good as the seals and techniques of cladding them; if water penetrates the cladding, the windows can rot in just a few years.  In addition, the vinyl or aluminum skins on these windows do not permit passage of vapor from the interior to the exterior, so that condensation forms on the inside of the skin.  Condensation = rot! (video)

• Reseal:  If the windows and frames are in good shape, but you have airtightness problems, it’s most cost-effective to apply some sealing around them. Caulk, weatherstripping and caulking cord are all products made for these purposes, and this video shows how to apply them.  In order to know where the air is coming in, you can do the following (houselogic.com):

• Seal the house by locking all doors, windows, and skylights.

• Close all dampers and vents.

• Turn on all kitchen and bath exhaust fans.

• Pass a burning incense stick along all openings -- windows, doors, fireplaces, outlets -- to pinpoint air rushing in from the outside. Smoke Pencil Pro ($44) is non-toxic smoke pencil for this purpose.

• Clean your windows and screens!  On windows where screens are installed, a bi-annual cleaning will greatly reduce the amount of mold present.  In general it’s not better to wash the outside or the inside first, as long as both are done!  However, since outsides usually get dirtier than the insides, it may be easier to see inside dirt if you wash the outside first. You can use a bucket of warm water with a few drops of dish detergent on the outside with a long-handled brush and squeegee, and TotalClean or a mixture of one part white vinegar to two parts water in a spray bottle for the inside. 

• Get your drapes in order!  If drapes are causing condensation to form on or around your windows, this is not a good situation and it will lead to mold if left unchecked.  Here are some suggestions:

• Open the drapes during the warm part of the day so that temperatures between the room and window can equalize and dry out moisture. 

• Leave the ceiling fan running in the room to promote circulation. 

• True thermal curtains are made of 3-4 layers of material, including a vapor retarder that allows vapor to escape through the curtain.   Problems can occur if the curtains block vapor.  

If you still have a high mold count near your windows, it’s best to check with a qualified, reputable mold inspector to find out the source and be able to enjoy the sun and scenery through your windows instead of the mold!

Photo by Rob Wingate on Unsplash