Although the Design-stage certification was to the Passivhaus standard, the best post-build air tightness test result only gave a reading of 0.9 which is not sufficient for the full Passivhaus certification (which must be 0.6 or lower). In principle it’s still possible to fix the air leaks and obtain Passivhaus certification but since that’s likely to be disruptive and to take some time I decided to proceed with Passivhaus Institute “Low Energy Building” certification instead.
The certification was done by Kym Mead; he sent the certificate a while back and I’ve just now installed the plaque.