Thats right, if you own a home in the CITY of Portland and want to sell it, starting in January 2018 you must get an energy audit performed prior to your home going on the market.  This applies to single family homes and attached homes too.  This means you must have this audit perfomed before you start marketing the property, which of course means while listing it.    The city projects this to cost $250 - $300 but of course as more inspectors come online, the cost may vary. 

The audit is designed to allow home buyers to compare the expected annual costs of energy and is also now up and running in a few other cities such as Austin, Texas and Berkeley California.   You can see an article about it here from The Portland Tribune, and also here a link to the City of Portland site. Note, if your home is listed before December 31st 2017 you are not required to have this performed.