With the evolution of building construction and poured concrete foundations, however, basements are now considered integral to a home's living space. Energy gurus and building codes routinely recommend these days that foundation walls be insulated. One way of accomplishing that is by adding a layer of rigid foam insulation on the outside of the foundation. The basements typically house the furnace, water heater, laundry machines and essential utilities. But recent trends have expanded the unfinished basement's utilitarian role into a more feature-rich, family-friendly environment such as a game room, home theater, office, craft or exercise area.