Last week I wrote about Elizabeth Turnbull’s experiment in green homebuilding on the Yale University campus, her tiny abode sharply contrasting the behemoth student dorms typical to most college campuses. Well, as it turns out, Turnbull isn’t the only one interested in small homes.

Taking a cue from coffee cups and Smurf Village, a Japanese designer-builder is marketing small, Styrofoam prefab houses that look like mammoth mushrooms. Each house is made from 100 per cent expanded polystyrene foam, which, unlike wood and metal, does not rust, rot or attract bugs. Oh, and each home can be assembled in a few hours—not bad for homeowners on the go.

While you likely won’t see these domed domiciles in your community anytime soon, polystyrene foam is becoming a popular building material in regular-looking homes.

Polystyrene foam is an excellent insulation material, which is why green-minded builders are turning to insulated concrete forms (ICFs, as they’re commonly known) for exterior foundations. The forms look like pieces of foam that come when you buy a fridge or TV, but when put together and filled with concrete, the forms provide a strong, rot-resistant, energy-efficient insulating base for exterior walls and foundations.

There are many ICF brands for foam insulation, some more suitable depending on the application. And while it tends to be slightly more expensive to build with, ICFs provide long-term savings when it comes to heating and cooling and rot-resistance.