Gambrel Roof Calculator

16 Foot Gambrel Roof Truss Calculator

A 16 ft gambrel is the largest span you can frame with 2×6 SPF #2 at 16 in on center, the cut-off width before lumber jumps to 2×8. It is the standard size for single-car garages, larger sheds, and small workshops that want loft storage above the main floor.

Lower Rafter
8.00 ft
Upper Rafter
4.14 ft
Total Height
8.00 ft
Knuckle Height
6.93 ft
Inner Width
8.00 ft
Attic Volume (20 ft L)
1749 ft³
Roof Area (20 ft L)
578 ft²
Recommended Lumber
2×6 SPF #2

Pre-Calculated Results for 16 ft Span

Sweep AngleLower RafterUpper RafterTotal HeightRoof Area (20 ft L)
45°11.310.008.00542
60°8.004.148.00578
67.5°6.126.128.00583

Loft Space at 16 ft

The loft floor across the knuckle is about 8 ft wide at a 60° lower sweep, with 8 ft of standing headroom directly under the ridge. That is enough for a workbench, a sleeping platform, or a generous storage mezzanine.

Door and Header Sizing

A 16 ft wall gives you room for a 9 ft × 7 ft overhead garage door with 3.5 ft of jamb on each side. The header above the door should be a doubled 2×10 with a continuous wind-load tie back to the gambrel knuckle if the building is in Wind Zone II or higher.

Typical Applications for a 16 ft Gambrel

A 16 ft wide gambrel is sized for garage, large shed, small workshop. With a 60° sweep angle the lower rafters land at 8.00 ft and upper rafters at 4.14 ft, both within the capacity of 2×6 SPF #2 for typical residential loads at 16 in on center rafter spacing.

Total roof height at the standard 60° sweep is 8.0 ft above the wall plate. Loft floor area inside the knuckle is approximately 8.0 ft wide and runs the full length of the building, usable for storage, a sleeping loft, or a workshop above the main floor.

Framing Tip
Do not size rafters for a 16 ft span from memory. Confirm the recommended 2×6 SPF #2 above against your actual snow load, since that default assumes a moderate 30 psf ground snow and needs to step up a size for anything heavier. It costs far less to order one size up now than to discover a sag after the roof is sheathed.

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Frequently Asked Questions

What lumber size do I need for a 16 ft gambrel?
For #2 SPF rafters at 16 in on center with moderate snow load (30 psf), use 2×6 SPF #2. Bump up one size for snow loads over 40 psf.
How tall is a 16 ft gambrel?
Total roof height equals half the building width in the half-circle method: 8.0 ft above the wall plate. Add wall height plus foundation height for total building height.
What is the rafter length for a 16 ft gambrel at 60° sweep?
Lower rafter 8.00 ft, upper rafter 4.14 ft (centerline measurements; subtract plumb and seat offsets for net cut length).

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