Steve Demetrick

Every home can be thought of conceptually as a six-sided box, with a lid (the roof or topmost ceiling), four sides (the walls), and a bottom (the basement floor or the slab). From an insulation standpoint, people often assume that insulating the slab is a waste of time because it sits on the ground. But while the slab may generate less heat loss than the walls or the roof, it should definitely be included when addressing a home’s overall insulation needs.

But how much insulation is needed in the slab? The answer comes from looking at the house as a system—at the amount of insulation, along with level of airtightness and the energy requirements, for the whole house. The effectiveness of insulation tends to max out if it’s not increased proportionally in all areas of the house. So if we insulated...

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