Attic Ventilation & Baffle Calculator
Adding insulation without keeping the soffits clear cooks your roof deck. This gives the ventilation area your attic needs and the baffle count to protect it.
Your project
Your results
- Net free vent area required
- 576 sq in
- Intake (soffit) — 50%
- 288 sq in
- Exhaust (ridge) — 50%
- 288 sq in
- Ridge vent length
- 16 ft
- Baffles required
- 60 baffles
- Material cost
- $288
4 sq ft at 1:300
Typical ridge vent gives 18 sq in per ft
One per rafter bay along the soffit
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
Gear for this job
Attic Ventilation Baffles
36 Pcs Attic Insulation Baffles for 24" Rafter Bays, 2" Air Channel | Black Polyethylene Rafter Vents,Improve Roof Ventilation,Prevent Insulation Blockage,Hassle-Free Installation
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UDV2248 Durovent Foam Attic Rafter Vent (Pack of 70) by ADO Products
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30 Pack 24 Attic Insulation Baffle, Sturdy Polypropylene Attic Baffles for 24" On-Center Rafter Bays with 2" Air Channel, Improve Roof Ventilation and Prevent Insulation Blockage
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Blown In Cellulose Insulation
Owens Corning R-19 Unfaced Fiberglass Insulation 77.5 Sq.ft (15 in x 93 in) 1 Batt
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Attic Measuring Rulers (Case of 400), 20 Inch, Card Stock, Attic Insulation R-Value Ruler for Insulators Ceiling Insulation
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DGSL Double Reflective Bubble Foil Insulation Foam, 23.6 in X 10 FT Aluminum Foil Thermal Insulation Radiant Barrier for Window, Garage Door, RV, Roof
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Attic Access Door Insulation Cover
DGSL Attic Door Insulation Cover, Attic Tent 25 x 54 x 11 in | Energy-saving attic stairway door ladder insulator with zipper
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Attic Door Insulation Cover 25"x54"x11", Energy Saving Tent Attic Stairs Cover Ladder Pull Down Insulator, R-Value 15.5 Thicken Aluminum Foil Stairway Insulation with Zipper Fireproof
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Attic Door Insulation Cover, Attic Stairs Insulation Cover, Attics Tent | Premium insulated, energy saving, airtight seal, zipper access, easy install, fits 25 x 54, blocks drafts
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How this calculator works
- Net free area = attic floor area ÷ 300 (or ÷ 150 without a vapor retarder)
- Split 50% intake at the soffits, 50% exhaust at the ridge
- Baffles = soffit length in inches ÷ rafter spacing
Frequently asked questions
Do I need baffles if I blow insulation in the attic?
Yes, anywhere insulation meets the soffit. Without baffles the loose fill blocks the intake vents and the whole ventilation path stops working.
Can an attic have too much ventilation?
Unbalanced ventilation is the real problem — more exhaust than intake pulls conditioned air up through ceiling leaks. Keep intake at least equal to exhaust.
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Net free vent area required
576 sq in