What attic ventilation means
Attic ventilation is the planned flow of outside air through an attic, in at the soffits and out near the ridge, to carry off heat and moisture.
Also called roof ventilation, net free area.
Where it matters on a roofing job
Poor ventilation shows up as mold on the deck, curled shingles and ice dams. Many shingle warranties ask for proper ventilation, so count intake and exhaust area on every reroof and write what you are adding on the estimate.
What the model code says
- The minimum net free vent area is 1/150 of the vented attic area. (IRC 2021, Chapter 8)
- It can drop to 1/300 when the code's listed conditions are met. (IRC 2021, Chapter 8)
Check which code edition your building department enforces for attic ventilation before you quote.
What it costs
The attic fan installation cost guide has the typical job at $540 and the usual range at $300 to $880. The guide shows its sources and what moves the price.
Work it out
- Cost guide: Attic fan installation cost
- Licensing: Roofing license rules by state
- Tools, templates and guides: Free roofing resources
Sources: 2021 International Residential Code, Chapter 8, Roof-Ceiling Construction (ICC). Checked October 9, 2026.