Types of Roof Rafters: Guide to Common Rafter Styles

Roof rafters are the angled framing members that give a roof its shape and structural support. This guide explains the most common types of roof rafters, their functions, and how to choose the right rafter style for a project. Understanding rafter types helps in design, estimating materials, and ensuring a safe, code-compliant roof.

Rafter Type	Primary Use	Key Feature
Common Rafter	Standard pitched roofs	Runs from ridge to wall plate
Hip Rafter	Hip roofs	Forms external roof corner
Valley Rafter	Intersecting roof planes	Creates internal angle for drainage
Jack Rafter	Short rafters near hips/valleys	Doesn’t run full span
Ridge Board/Beam	Roof peak support	Aligns and connects rafters

Overview Of Rafter Roles And Terminology

Roof rafters transfer roof loads to bearing walls and support sheathing, underlayment, and roofing materials. Key terms include ridge, plate, birdsmouth, hip, valley, jack, and collar ties. Knowing these terms clarifies rafter layout and load paths for framing and inspection.

Common Rafter

The common rafter is the most frequently used rafter in conventional framed roofs and runs from the ridge board to the wall plate. It defines the main roof slope and spacing (commonly 16″ or 24″ on center) and carries uniform loads across its length.

Hip Rafter

Hip rafters form the external angle where two roof planes meet and run diagonally from the ridge to the building corner. Hip rafters are larger and carry loads from adjacent jack rafters, so they must be sized carefully and often require additional support at the ridge and eaves.

Valley Rafter

Valley rafters occur where two roof planes intersect inward, creating a channel for water drainage. They support valley jack rafters and must accommodate concentrated water flow, requiring careful flashing and sometimes wider material to resist rot and deflection.

Jack Rafter

Jack rafters are shortened rafters that tie into hip or valley rafters rather than the ridge board. They fill the roof field near hips and valleys and must be cut precisely to maintain consistent roof pitch and aesthetic lines.

Ridge Board And Ridge Beam

The ridge board is a non-structural alignment member at the roof peak, while a ridge beam is structural and supports loads from rafters. Where rafters bear on a ridge beam, the beam reduces outward thrust on walls and may allow for larger open interior spaces.

Collar Ties And Rafter Ties

Collar ties and rafter ties prevent rafters from spreading under load. Collar ties are installed in the upper third of the rafters, while rafter ties are near the ceiling level. Properly placed ties are essential to resist wind uplift and horizontal thrust that can push walls outward.

Birdsmouth Cut

The birdsmouth cut is a notch at the rafter heel that allows it to seat securely on the wall plate. It creates a bearing surface and resists lateral movement; building codes limit the depth of the notch to preserve rafter strength.

Common Materials And Sizes

Dimensional lumber (commonly Douglas fir, southern pine, or spruce-pine-fir) is the traditional material for rafters. Engineered wood products like laminated veneer lumber (LVL) or parallel strand lumber (PSL) are used for long spans or heavier loads. Typical common rafter sizes range from 2×6 to 2×12 depending on span, load, and spacing.

Load Considerations And Sizing

Rafter sizing depends on dead loads (roof sheathing, underlayment, roofing), live loads (snow, maintenance), and wind loads. Local building codes and climate determine design loads. Using span tables or load calculators helps ensure rafters are sized to meet code and avoid excessive deflection.

Roof Pitch And Rafter Cuts

Roof pitch influences rafter length, birdsmouth geometry, and the angle of cuts. Steeper roofs have longer rafters and different wind and snow performance characteristics. Accurate rafter layout requires calculating rise, run, and diagonal cuts, often using framing squares or software to reduce waste and errors.

Common Roof Framing Methods

Stick framing uses individual rafters cut on-site and assembled over a ridge board or beam. Truss systems use prefabricated trusses to span large distances and speed installation. Trusses reduce jobsite labor but limit attic access and require precise engineering and installation.

Installation Tips And Best Practices

Layout rafters from the ridge outward, verify ridge alignment, and install temporary bracing until sheathing stabilizes the roof. Ensure birdsmouth cuts are seated fully on the wall plate and use hurricane ties or metal connectors where required. Accurate layout, consistent spacing, and secure connections reduce callbacks and improve long-term performance.

Water Management Around Hips And Valleys

Hips and valleys are vulnerable to leaks due to intersecting planes. Proper flashing, underlayment, and valley lining are essential. Install closed or open valleys according to roofing material recommendations and ensure adequate slope and drainage to prevent ponding and ice buildup.

Choosing The Right Rafter Type For A Project

Choice depends on roof geometry, span, budget, and desired interior space. Trusses are cost-effective for simple spans, while stick framing with rafters is preferred for custom rooflines and vaulted ceilings. Consider maintenance access, ventilation, and insulation strategy when selecting rafter and framing method.

Inspection And Maintenance

Inspect rafters for signs of rot, insect damage, cracked members, or excessive deflection. Check connections, metal ties, and roof sheathing integrity. Early detection of moisture infiltration at valleys, eaves, and penetrations prevents structural degradation and costly repairs.

Building Codes, Permits, And Engineering

Local building codes specify required loads, rafter spacing, and fastening schedules. For unusual spans, complex roof geometry, or heavy loads, engineered plans or an engineer’s stamp may be required. Complying with codes and working with an engineer mitigates risk and ensures insurance and resale compliance.

Cost Factors And Material Comparisons

Cost varies by lumber species, engineered product selection, labor complexity, and roof complexity. Trusses reduce labor but add design and transportation costs. Engineered beams increase material cost but reduce the number of supports. Balance initial material cost with long-term durability, maintenance, and desired interior layout.

Examples Of Rafter Layouts

Simple gable roofs use common rafters with a ridge board and rafter ties; hip roofs incorporate hip rafters and hip jacks; cross-gable roofs require valley rafters and valley jacks. Clear, scaled layout drawings reduce waste and ensure consistency during construction.

Resources And Tools For Layout And Design

Useful tools include framing squares, rafter tables, online calculators, and CAD or framing software. Manufacturer guides and local code books assist in choosing lumber grades and connectors. Professionals often use structural engineering software for complex roofs to model loads and deflection.

Safety Considerations During Rafter Work

Working at height requires fall protection, safe scaffold or ladder use, and personal protective equipment. Secure temporary bracing to prevent collapse during framing. Adhering to OSHA and local safety regulations protects workers and reduces liability.

Signs A Roof Needs Rafter Repair Or Replacement

Look for sagging rooflines, cracked rafters, ceiling cracks, or exterior wall separation. Persistent leaks, rot, or insect damage at critical connections also indicate rafter issues. Structural assessment by a qualified contractor or engineer identifies repair options like sistering rafters, adding beams, or full replacement.

Frequently Asked Questions

How Are Rafters Different From Trusses? Rafters are single framing members assembled on-site for custom shapes; trusses are prefabricated engineered assemblies for quick installation.

When Is A Ridge Beam Required? A ridge beam is used when rafters do not provide opposing support, such as long spans or vaulted roofs, to reduce outward thrust on walls.

What Is The Typical Rafter Spacing? Common spacing is 16″ or 24″ on center, but span tables and roofing material requirements determine final spacing.

Further Reading And Standards

Refer to the International Residential Code (IRC), local building codes, and lumber grading standards for prescriptive rafter sizing and connection details. Technical bulletins from engineered wood manufacturers provide span tables and installation guidance for LVL and I-joists used as rafters.