Just in case you didn’t believe us…Air carries A LOT of water vapor!

We’ve mentioned air sealing your home A LOT in this blog, because those big and small gaps in the envelope between the nice, conditioned inside and the unconditioned, sometimes polluted outside make a big difference!  A big difference in:

• Indoor temperature

• Indoor humidity

• Indoor particulates

• Indoor VOCs

The building science professionals have been talking about water vapor movement since the 1980’s, and recently just revisited their calculations.  There’s two ways water vapor (read: humidity) can get into your home.  Diffusion is the movement of the vapor through a solid, such as a sheet of drywall.   Now, nobody lives in homes that only have drywall walls, but this is a reference point because taped and mudded drywall, even coated with enamel paint, can let some moisture through.  A little.  However, it’s nowhere near the amount of water vapor that can get into your house if there’s just a 1”x1” hole in that 4x8’ sheet of drywall.  Check out the illustrations in a new article by Dr. Joe Lstiburek of Building Science Corporation:

The above examples show the amount of water that can leak into your home through a solid drywall panel (which in reality we do add other materials on the outside) vs. a drywall panel that has a 1x1” hole in it.  In both climates, the panel with a hole in it allows a lot more water through–carried in the air.  Over a Chicago winter, this small hole will let in 95 quarts of water–200 times what the drywall alone will do.  Over an Atlanta summer, this small hole will let in 30 quarts of water, 100 times what the drywall will allow. 

Air carries A LOT more water vapor than materials like drywall.  While a 1x1” hole can be easily seen and plugged, this is just for illustration.  Think about 1/16” gaps around windows, baseboards, electrical outlets or ceiling fixtures.  These can easily add up to DOZENS of square inches.   

OK, so what are the consequences of these little gaps?

• They make your heating and air conditioning work harder (more energy needed to heat, cool and dehumidify to the same levels)

• There’s also more particulates carried in with the air, if you live in a dusty or urban or wildfire-prone location.

• There’s more VOCs and NOx carried in with the air, if you live in an urban or wildfire-prone location.

For me, this was a great example of a picture being worth a thousand words, or worth that extra “nudge” to seal the gaps!  The above referenced article was sent to my inbox by buildingscience.com–well worth the read!

Photo by Hailey Tong on Unsplash