Maximum Span for 2×6 Roof Rafters

The maximum span for 2×6 roof rafters depends on species, lumber grade, rafter spacing, roof live and dead loads, snow load, roof slope, and how the ridge is supported. This article summarizes key span values, explains the factors that control allowable span, and shows how to use span tables and simple checks to determine whether a 2×6 rafter is appropriate for a specific roof. Always verify spans with current building codes or a structural engineer for critical cases.

Rafter Spacing	Typical Max Span (No.2 SPF)	Typical Max Span (Douglas Fir-Larch No.2)	Typical Max Span (Southern Pine No.2)
24″ O.C.	~8’–10′	~9’–11′	~9.5’–12′
16″ O.C.	~10’–12′	~12’–14′	~12.5’–15′
12″ O.C.	~11.5’–13′	~13’–15′	~14’–16′

Sample scenario: No.2 Southern Pine rafters, 16″ OC, 10 psf dead + 20 psf live, simple support. Span tables or design calculations indicate an allowable rafter span around 12.5’–15′10–12′

How To Use Span Tables Effectively

To use span tables: identify lumber species and grade, select the correct rafter spacing and roof load assumptions, choose the table row matching roof slope if applicable, and read the maximum allowable span. If the exact combination is not listed, choose the next more conservative (shorter) span or get an engineered design.

When To Call A Structural Engineer

Engage a structural engineer for unusual loads, long spans near or beyond typical table values, complex roof geometry, heavy snow zones, or when cutting or modifying rafters in existing structures. An engineer will provide load calculations, member sizing, and connection details. Professional review is recommended whenever building safety could be affected.

Summary Checklist For Determining Max Rafter Span

• Identify species and grade of 2×6 lumber to determine strength values.
• Determine rafter spacing (24″, 16″, 12″ OC) — tighter spacing increases span.
• Use appropriate loads (dead + live + applicable snow) from local code or ASCE 7.
• Check span tables from IRC or manufacturer for exact allowed spans and deflection limits.
• Account for birdsmouth, bearing, and connections that reduce section or capacity.
• Consult an engineer for long spans, heavy snow, or complex conditions.

Resources And References

Useful references include the International Residential Code (IRC) span tables, lumber manufacturer span charts, ASCE 7 for snow loads, and local building department guidance. These authoritative sources provide the exact tabulated values needed for permit-ready designs.

If necessary, the next step is to consult the IRC span tables with the exact species, grade, rafter spacing and governing live load to obtain the allowable span for the specific project or to request an engineered design when conditions are outside prescriptive limits.