Tad Everhart, an energy adviser from Portland, Oregon, shares his story of building a house . . . which he retrofitted 10 years later after learning about Passivhaus. We find out why he was motivated to take on the challenge, how he went about it and whether all the hard work was worth it.

Professor Tom Woolley from Rachel Bevan Architects explains what hempcrete is, how it is mixed and applied, and what the pros and cons of using it are.