Massachusetts is supposed to adopt the 2012 IECC by July or August, 2013. When that occurs, ceiling insulation will go to 49, basement or crawl space walls will be at 15 continuous or 19 cavity, and blower door testing will be required. House tightness increases from 7 ACH50 to 3 ACH50. That is pretty tight. Post construction duct tightness goes from 12% Total leakage to 4% Total leakage. The rough in tightness with no air handler goes from 4% to 3%.
I just tested a small addition this week: 465 square feet. I tested the ducting on rough-in with no air handler. At 4% the leakage limit was 18.6 cfm. Good contractor. Joints nicely taped. The leakage was 29 cfm. That meant that he had to find holes the size of (3) ball point pen diameters! He did. And that posed another problem.
At those low leakage numbers, the duct tester couldn't give me a reading. I had to increase the pressure up to over 50 Pascals before I got an airflow reading. To get an accurate number at 25 Pascals, I will have to decrease the size of the ring on my duct tester.
The point is that when the requirement drops to 3% at rough in, the flow will be 45 for a 1500 square foot house and that will start to be marginal with the equipment.
But are we ready for 3 ACH50 homes? Remember that the existing Stretch Code is 7 ACH50.