In this video, Matt Risinger and builder buddy Doug Cameron set out to solve a building science mystery. Cameron built this new house using his Zip System 2.0 method which should yield a very airtight house, but his blower door score is not what he expected. Watch to find out how he solved the problem and what the source of the extreme leakiness was.

But first, what is a blower door score? Take out the front door, pressurize the house, and measure how much air is leaking through the envelope. A passive house standard has a blower door score of 0.6 air changes per hour, pressurizing the house to 50 pascals. Code only requires a blower door score of 5.0, so that tells you how tight these houses are. As you will learn, this specific house had a blower door score over 1.0, so they set out to find the leaks. Cameron and his team used a smoke pen to find the leaks; the main culprits were the windows and doors.

Follow along to see how to troubleshoot when your house isn't as tight as you'd like.