We’ve been living in our house for over a year now and last June when the weather became hot we noticed a smell in the air that was characteristic of tar paper and foam; not a smell you’d want to live with and probably not healthy to breathe. It was a little disconcerting so the investigation began. I checked several void spaces near the roof that hadn’t been sealed yet since the airspace could allow fumes to travel into the house and pick up smells from the foam and tar paper. While sealing I noticed the smell was percolating through the gaps in the pine ceiling. Hmm…more sealing to do but why was it coming in through there? At this point, I began a long process of caulking gaps and cracks that led to the roof panel. I also started asking questions of people that dealt with air handling and green home design.

The conclusion: Since this smell only occurs when it’s over 80 degrees and sunny, the probable explanation is that the heating of the roof metal creates a temperature difference between the area under the roofing and inside the house. Pretty obvious, but what happens is this difference creates negative pressure inside the house thereby driving the fumes inside.

It’s odd that the process of building an energy efficient house can create other problems. These issues didn’t rear their heads in older homes because leaks were many, air moved through them rapidly, and pressure differences weren’t great. With tight, efficient home ventilation, it is key to take steps to change your air regularly and seal penetrations to eliminate these issues.

How did we solve this? I’m confident I did but we’ll see when the 100 degree weather comes. So far, with temperatures to 94 degrees we haven’t had the smell yet… There are companies that look at various energy issues in the home like electricity use, water consumption, air handling and perform what is called an energy audit. In the air handling aspect, they use a blower door which is a large fan that can simulates different pressures in your home that reveals leaks and shows you how often the home’s air is changed naturally or by forced ventilation (i.e., your furnace fan or whole house fan). This is a special fan that is calibrated so you can see exactly how much air is moving through it revealing how much air is moving through your home. There are some fancy calculations you can do that can reveal your air changes per hour (ACH) and thereby show you how tight your home is and if it’s too tight making it unhealthy to live in.

What we did: We hired Mike Carlton of Palouse Synergy Systems (www.palousesynergy.com) to come to our home and run a blower door test. Mike was able to negatively pressurize our house simulating this hot weather condition we experience. Within a minute of sucking the air out of the house, I could smell the tar/foam in several areas. With a smoke puffer located at several points where the air was leaking in, bring the smell with it. The main culprit was around the rafters where they went through the wall of the house. During installation of the rafters, we foamed/caulked around them but they shrunk over the year pulling away from the wall and creating a small gap that allowed air through. I went to work with the caulking gun and to date the smell hasn’t reared its ugly head again.

In addition to finding leaks, Mike was able to calculate our ACH of the house to see if it is too tight or not. The test revealed our ACH at 0.65 (the air changes itself in the house 15 times per day naturally), ideal for energy efficiency and healthy air.

The blower door test was an excellent way to help solve our indoor air quality problem and also show potential sources of energy loss. I’d recommend this test for any home as a step to improve energy efficiency by reducing drafts and when building a new home to show potential sources of future problems.