What is an attic in a house, and what does it do?
Common types of attics
- Unfinished attic: open framing with insulation on the floor, reached by a hatch or pull-down stairs.
- Truss attic: built with factory trusses whose web members crisscross the space, which limits storage and makes conversion difficult.
- Stick framed attic: rafters and ceiling joists cut on site, which leaves more open space.
- Finished or bonus room attic: living space under the roof, with knee walls and sloped ceilings.
- Sealed or conditioned attic: insulation, often spray foam, applied to the underside of the roof deck so the attic stays close to indoor temperature.
The parts you will find up there
Looking up, you will see the roof decking (plywood or OSB) on rafters or trusses. At the low edges are the soffit vents that bring in air, and at the top, a ridge vent or other exhaust. On the floor, insulation sits between the ceiling joists. Plumbing vent pipes, bath fan ducts, and gas appliance flues pass through on their way to the roof.
Why the attic matters to your roof
In a vented attic, air should move in at the eaves and out near the peak. That airflow carries away summer heat and the moisture that leaks up from the house. When ventilation is blocked or bath fans dump into the attic, the decking can mildew and soften, nails rust, and shingles age faster. The attic is also where many roof leaks show up first, as stains on the decking or wet insulation. Learn more in roof anatomy explained and roof ventilation basics.