“Breaking” the Air (tightness) Barrier

At 0.99 ACH50, we broke the magical (in our minds!) 1.0 barrier. This is a very air tight home!

After our somewhat disappointing blower door test last week, we threw some mud at the walls (well, we placed it carefully around the edges of the wall), did some taping and caulking, and then had Ross and Kat Elliott of HomeSol Building Solutions come by to do our official blower door test.

We went from a code-compliant 3.1 ACH50 (air changes per hour at 50 Pascals) to an almost PassiveHaus compliant 0.99 ACH50! We could feel some small areas of leakage to be addressed (almost all were failures of the Tuck Tape to properly adhere and seal against the air barrier membrane!). After the test, we realized that we hadn’t covered over the sump pit in the basement, and so we think we can do even better on the final test once the house is finished. Ross suggested that it’s common to improve the air tightness by around 20% once all the interior wall and ceiling sheathings are in place.

Even if we end up slightly shy of the 0.6 mark, we are very excited to have built a house that far surpasses the air tightness of conventional building, and to have done that using mostly straw bale walls and even clay plasters. It’s an indication that the use of natural building materials and “alternative” methods can be part of an extremely tight and energy efficient building.

Our thanks to all the students whose constant awareness and vigilance regarding air tightness as we built the house helped to ensure that this result was possible. Way to go, Graham Wise! And our thanks to Matt Caruana for last week’s test… we wouldn’t have achieved this score without a first kick at the can!

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