Three words…minimum building code! More specifically, insufficient insulation detailing, vapour barriers that are inevitably punctured, uncontrolled thermal bridging, poor quality windows (80% of the market is single glazed!) and dated construction techniques. To summarise, poor building envelopes! To make up for these subpar practices, air-conditioners and heaters are required to make up for all of that energy loss which ends up costing homeowners each and every year.