How do attic ventilation and attic insulation work together?
Short answer. Attic insulation and attic ventilation do different jobs: insulation on the attic floor slows heat flow between the attic and your living space, while ventilation above it carries heat and moisture out of the attic. They work together only if the insulation does not block the soffit vents and the ceiling below is air sealed.
Who does what
- Insulation keeps summer attic heat from radiating into bedrooms and keeps winter heat in. ENERGY STAR currently recommends about R-49 for an uninsulated attic in Climate Zone 3, which covers much of Georgia, and R-60 in Zone 4, which includes the northern mountain counties.
- Ventilation protects the roof: it removes heat that would bake the shingles and moisture that would condense on the decking.
- Air sealing is the link between them. Gaps around light fixtures, top plates, and the attic hatch let humid indoor air into the attic, which ventilation then has to remove.
Where they collide
The most common mistake is blowing insulation right into the eaves. It feels thorough, but it chokes the soffit intake. The code calls for at least a 1 inch air space between insulation and the roof sheathing at the vents. Rafter baffles, sometimes called vent chutes, hold insulation back and keep a clear channel from each soffit vent into the attic.
The right order of work
- Fix roof leaks and moisture sources, like bath fans that vent into the attic.
- Air seal the attic floor.
- Install baffles at every rafter bay with a soffit vent.
- Add insulation to the target depth.
- Confirm exhaust and intake are balanced.
Sealed spray foam attics are a separate design where insulation moves to the roof deck and the vents are closed. See roof ventilation basics and heat, humidity, and roof life.