A blower door test was done on the house a while back. The  upgrades have been completed on the house and were ready to re-assess the house.  But, an addition was added to the house, and I'm not sure how to compare results because the Volume is now larger.  Any info will help.

ACH50 should be your comparison metric, and whoever did the blower door test should be able to convert the CFM50 they measured on the fan into an ACH50 for each building.

ACH50 = air changes per hour @ 50 pascals, CFM50 = cubic feet per minute @ 50 pascals. The math is very simple, 60 minutes / hour, and cubic feet / existing building vs. cubic feet / new building.

European air tightness standards aim for maximum levels of ACH50 to allow comparison between different sizes of buildings. (passivhaus is < 0.6 ACH50, for example).