• Figure you'll need to beef up the floor, insulate—and more. Here's a look at some building-code basics when it comes to turning attic space into living space.

    Access and egress
    Code generally requires a full-size staircase with a minimum 6-foot 8-inch clearance above it. For fire safety, there must be two ways out—a second staircase, for example, or a window.

    Ceiling height
    Any living space requires at least 7 feet of headroom over a floor area of at least 70 square feet, measuring at least 7 feet in each direction. At the Lyons' house, this meant that only a portion of the attic was usable, though some of the low-clearance area was tapped for storage.

    Floor support
    Attic floors generally need to be reinforced with additional joists and a subfloor. The Lyons used a web of 16-inch-deep engineered trusses to accommodate wiring, plumbing, and ductwork, then topped the plywood subfloor with oak or tile. (Keep in mind that deep trusses will cut into headroom.) "Houses built before 1950, and some built after, may also need foundation work," says architect Stewart Davis, especially if the project involves raising the roof, as the Lyons' did.

    Ventilation and insulation
    Heat and moisture rise. This often means having to add air-conditioning, ceiling or window fans, and/or windows. The Lyons installed windows at each end of the roof to promote cross-ventilation. A layer of spray foam insulation under the roof and in the walls will help cut their heating and cooling costs.
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