What does the barn roof (gambrel) calculator compute?

It estimates ridge height, break height, rafter lengths for lower and upper segments, frame counts by spacing, roof surface area, and sheathing coverage. Results are for planning only, not structural use.

Can I use this to design a gambrel barn roof?

Yes — for conceptual design and material planning. Use engineered drawings for construction.

🏚️ Barn Roof (Gambrel) Calculator

Estimate gambrel roof geometry, ridge height, lower and upper rafter lengths, frame counts, roof surface area, and 4×8 sheathing coverage

This barn roof calculator provides geometric planning for classic gambrel roof designs — used in barns, sheds, and lofted garages. Enter your building width, length, and desired slopes to calculate ridge & break heights, rafter lengths, number of trusses, and sheathing.

Note: This tool is for estimation and visualization only — not a structural engineering calculator.

🏠 Building Width (ft) Eave-to-eave total width.

📏 Building Length (ft) Used to calculate frame/bent count.

⬆️ Lower Pitch (rise:12) Typical: 7–10 for steep lower slope.

↗️ Upper Pitch (rise:12) Typical: 3–6 for shallower upper slope.

📐 Break Position (% of half-span) 0.4 = 40% of half-span from eave to break point.

🪜 Overhang (inches, per eave) Adds horizontal projection each side.

🧱 Frame Spacing (inches) Common values: 16, 19.2, 24.

Results will appear here

🔧 Recommended Roofing Tools & Supplies

Disclosure: This section contains affiliate links. As an Amazon Associate, we earn a small commission from qualifying purchases — helping us keep SmartRoofingCalculator free to use.

📌 Enter width, length, lower & upper pitches, break %, overhang, and spacing.

💡 Tip: A 30′-wide barn with 8:12 lower and 4:12 upper pitch gives about a 10.5′ ridge height.

✅ Best Practices for Designing Gambrel Roofs:
• Keep lower slope steeper (7–10:12) for wall clearance.
• Place break point around 35–45% of half-span for balanced shape.
• Ensure adequate ridge ventilation to prevent condensation.
• Use structural gussets or metal plates at the break joint.
• Sheathing area ≈ total roof surface ÷ 32 for 4×8 panels.
• Always verify local snow & wind load code compliance.
• Consult an engineer for load-bearing designs before framing.

Related Calculators: Roof Pitch Calculator • Plywood Estimator • Roof Area Estimator