How Air Sealing Solved My House of Horrors

I used my home for a test case. It was built in 1961 and is in the western suburbs of Chicago.  It is a 1,900-sq. ft. ranch with a full basement. A blower door is a frame covered with a vinyl material and has a fan mounted in the middle.

I set it up in the front door of my home and closed all of the exterior doors and windows. The goal is the run the fan and create either a negative or positive differential pressure of 50 pascals in between the house and outside. Once you hit 50 pascals of differential pressure, you look at how many cubic feet per minute is moving through the fan. That number is the CFM50  and had measured leakage of over 3,000 CFM50, which is not good for its size.

Our subdivision is like a rural bubble in an otherwise urban area, surrounded by countless trees on the property. Living with nature means we must also deal with bugs, spiders, and mice constantly trying to invade our home in search of a warm shelter during the cold winter months. 

There were two key features that were left out of the real estate listing when we bought our home. The first was the mice that would constantly find their way into the kitchen cabinets throughout the fall and winter. The second was the spiders that would create intricate webs strewn about the rim joist of our unfinished basement. It would be an understatement to say that these unwanted guests have caused added stress to my home life. My family would dread doing laundry in the spooky basement and be horrified if a mouse came into contact with the plates or silverware in our kitchen.

The Work Begins

Two years ago, I decided to start air-sealing my basement. I purchased a few froth packs, which is the homeowner’s DIY version of closed-cell spray foam. I went to work insulating the rim joist. The rim joist is a 2×8 that sits upright on top of a bottom plate that wraps around the perimeter of the home. I sealed the rim joist to the floor joist and then sealed the rim and floor joist to the bottom plate. 

Another leakage point was the gap between the bottom plate and the concrete foundation.  This assembly was the source of most of my basement leakage. I could not seal the north wall because the last floor joist was running parallel to the foundation and was so close I couldn’t fit my hand or spray foam gun into the cavity, but more on that later.