What is the proper way to vent a roof, step by step?
Short answer. The proper way to vent a roof starts with deciding whether the attic will be vented or unvented, then sizing the net free area from the attic floor and choosing one exhaust type and an intake type that fit the roof's shape. Exhaust goes high and intake low, with intake at least equal to exhaust, and everything is installed to the manufacturers' instructions with clear paths between them.
Step 1: vented or unvented
Most Georgia homes use a vented attic with insulation on the floor. An unvented attic, with insulation applied to the underside of the deck, follows a separate set of code rules and gets no vents.
Step 2: size it
Divide the attic floor area by 300 for balanced high and low vents, or 150 otherwise, then multiply by 144 for square inches of net free area. Split it between intake and exhaust.
Step 3: choose exhaust
- Long ridge: ridge vent.
- Short or broken ridges: box vents high on the slopes, or a vent approved for hips.
- One type only per attic.
Step 4: choose intake
- Deep overhangs: vented soffit or strip vents.
- Little or no overhang: an intake vent at the roof edge.
Step 5: place it
- Exhaust within 3 feet of the ridge, measured vertically.
- Intake at the lowest point of the roof.
- Each separate attic space gets its own intake and exhaust.
Step 6: open the path
Baffles at every vented eave bay, holes cut in any backing, insulation kept 1 inch below the deck.
Step 7: install and isolate
Cut slots and openings to spec, use the specified nails, close old competing vents, and duct every exhaust fan outdoors on its own cap. See roof ventilation basics and ridge vent vs box vents.