UP TO code
Any attic conversion is subject to building codes for safety reasons that may not at first be apparent, such as structural support and fire hazards. Other attic-specific requirements cover headroom, floor space, access and egress, windows and light, heating and cooling, and ventilation.
HEADROOM
Attics in the oldest homes rarely meet modern codes for height, which require ceilings be at least 7 to 7 ½'. Yet some are barely 6' tall. Other roofs are supported by trusses that cross the space at a midpoint between the floor and ridge pole, making minimum ceiling heights impossible. At least half of the usable space should have ceilings at least 7' or higher. New flooring, insulation, and drywall or wood finishes may cut into the available room height.
FLOOR SPACE
The minimum for a new attic room is 70 square feet. (The smallest dimension must at least 7'.) While that may seem tiny, consider that a significant amount of the footprint is usually tucked under eaves that are less than head height. As a good rule of thumb, make sure there is at least 70 square feet with an overhead height of at least 6'.
SUPPORT
Attics in older homes were never intended to be load-bearing: that is, to hold the weight of people, furniture, and bathroom fixtures. Many were built with “dead
load” weights of 10 pounds per square foot or less. Minimum live loads—the requirement for habitable space—are three or four times that. Meeting the standard will usually mean improving joist support under the floor and strengthening rafters overhead, and may even involve engineered improvements such as tie-rods. Complex projects will require a structural engineer.
ACCESS AND EGRESS
How will you reach the attic? A fixed stair is usually a minimum requirement, along with a second point of access (usually a window). While it’s possible to buy a spiral-stair kit that meets code and fits in as little as 5 square feet, ask yourself whether you want to climb that stair every day, if the new space is intended as a main bedroom. What about getting furniture up to the space? Architect Frank Shirley says: “Spiral stairs are my last option to get from one floor to another.”
WINDOWS & LIGHT
Codes require that at least one window be equal in dimension to 8 percent of the usable floor area. For
150 square feet of usable space, that equates to a small single window or skylight (3' x 4'). In most cases, you’ll want multiple windows or skylights, one of which is large enough to permit escape in an emergency. In that instance, add a fire escape or escape ladder to the budget.
HEATING & COOLING
Any attic conversion must have a fixed source of heat (portable heaters usually don’t meet code) and be able to maintain a temperature of 68 degrees F. Since most attics tend to trap heat, it makes sense to add or extend whole-house HVAC to the attic, or to add a mini-split unit that serves the new space. For the same reason, it’s essential to insulate all walls and ceilings, either with sprayfoam or batt insulation.
VENTILATION
Before spray foam or batt insulation goes in, create a 1" air space from soffit to ridge by using rafter vents or insulation baffles. The vents create narrow gaps that allow fresh air from the soffit vents to flow up and out through the ridge vent, to avoid moisture problems.