ACH2.0 in most of the upper part of the country is pretty aggressive. The 2015 ICC isn't a slouch either -- say you're in Chicagoland building a new home, this would mandate R49 in the attic, R20 in the walls (or R13 in the bays + R5 exterior), R15 on basement walls, R30 in the floors.

It could of course be much more aggressive, and likely will be eventually, but if you had a ACH2 house with those insulation values, minimum U-0.3 windows, >0.94 efficient gas furnace / high quality heat pumps, it would be a very efficient house.

Table R402.1.2 here: https://codes.iccsafe.org/content/IECC2015/chapter-4-re-resi...