PORTLAND, United States (CHRISTIAN SCIENCE MONITOR) – Rubbing their hands and breathing dragon smoke into the cold air, residents rush inside the bright green building.

The temperature outside has barely hit double digits Fahrenheit, so the warm lobby inside Bayside Anchor, a low-income apartment building in Portland, Maine (United States), is a happy reprieve.

The lobby is also an architectural feat, as Bayside Anchor has no centralised heating system.

It is a certified “passive house,” which means the building has airtight insulation and thick windows to keep the interior warm and heating costs low.