Inputs
Example data table
Click "Load" to populate the form with a scenario.
| Scenario | Unit | Segments | Setback | No‑vent | Piece / Overlap | NFA / Ratio | Attic area | |
|---|---|---|---|---|---|---|---|---|
| Simple gable | Imperial | 1 × 40 ft | 0.5 ft | 2 ft | 4 ft / 0.17 ft | 18 in²/ft / 1:300 | 1200 sq ft | |
| Hip roof | Imperial | 3 × 20 ft | 0.5 ft | 3 ft | 4 ft / 0.17 ft | 14 in²/ft / 1:150 | 1800 sq ft | |
| Metric duo | Metric | 2 × 12 m | 0.15 m | 0.5 m | 1.2 m / 0.05 m | 120 cm²/m / 1:300 | 150 m² |
Formula used
- Available ridge length (per segment) = max(0, SegmentLength − 2×EndSetback − NoVentZones).
- Total available ridge = sum of available length across all segments.
- Total NFA required = AtticArea / Ratio.
Units: in imperial, area in ft² ⇢ NFA in in² (multiply by 144). In metric, area in m² ⇢ NFA in cm² (multiply by 10,000). - Exhaust NFA = TotalNFA × ExhaustShare.
- Length by NFA: imperial → ExhaustNFA(in²) / NFAperFoot(in²/ft); metric → ExhaustNFA(cm²) / NFAperMeter(cm²/m).
- Effective piece coverage = max(0, PieceLength − Overlap).
- Recommended install length = min(AvailableRidge, LengthByNFA). If LengthByNFA > AvailableRidge, additional exhaust is required elsewhere.
- Quantity with waste = RecommendedLength × (1 + Waste%).
- Pieces needed = ceil(QuantityWithWaste / EffectivePieceCoverage).
- Boxes needed = ceil(PiecesNeeded / PiecesPerBox).
How to use
- Select your unit system and optional waste percentage.
- Add ridge segments, setting end setbacks and no‑vent lengths per segment.
- Enter product piece length, overlap, and packaging details.
- Enter attic area, ventilation ratio, exhaust share, and vent NFA per length.
- Click Calculate. Review geometry‑available versus NFA‑required length and any shortfall warning.
- Export your results to CSV or print a PDF‑ready report.
FAQs
Check your vent’s datasheet. Many ridge vents provide 12–20 square inches per foot, but values vary by brand and model. Enter what your specific product guarantees per linear length.
Many codes allow 1:300 with an effective vapor retarder and balanced intake/exhaust. Otherwise use 1:150. Always verify local requirements, climate, and roof assembly details with your authority having jurisdiction.
Many manufacturers show approximately 6 inches (0.5 ft) from ends, but specifics vary by product and shingle layout. Use the datasheet and align with shingle cap requirements and wind zone guidance.
Yes. Overlap between adjacent pieces shortens effective coverage per piece. Enter the joint overlap so the calculator uses net coverage rather than nominal piece length when counting pieces and boxes.
Enter each hip or ridge as a separate segment. Use no‑vent lengths for intersections, ridge terminals, or obstacles where venting is not permitted or would be ineffective.
The tool flags a shortfall. Consider supplemental exhaust, such as roof louvers or a code‑approved alternative. Also ensure intake NFA is sufficient; inadequate intake can throttle exhaust performance.
Results
Available ridge by geometry
0.00 ft
0.00 m
Required length by NFA
0.00 ft
0.00 m
Recommended install length
0.00 ft
0.00 m
Effective coverage per piece
0.00 ft
0.00 m
Pieces needed (with waste)
0 pcs
Boxes needed0
Leftover pieces if boxed0
Cost using pieces
$0.00
Cost using boxes
$0.00
Shortfall: Required NFA length exceeds available ridge. Add other exhaust.