Roof rafters are sloping structural members that support a roof’s sheathing, roofing materials, and other loads. Their shape and placement depend on the roof design, so a house may use several rafter types at once. Knowing the difference between common, hip, valley, and jack rafters helps homeowners understand roof plans and communicate with builders. It does not replace structural design: rafter size and spacing must account for local building codes, span, lumber species, snow, wind, and other loads.
What Roof Rafters Do
In conventional stick framing, rafters run from the roof’s lower edge, often at an exterior wall, toward a ridge or another supporting member. Together, they form the roof’s sloping framework. Roof sheathing is fastened over the rafters, and the roofing system is installed above it.
Rafters transfer roof loads to the building’s supporting structure. Those loads can include the weight of framing and roofing, temporary construction loads, snow, and wind uplift. The exact path depends on the roof design. A rafter may bear on a wall, ridge beam, hip, valley, or other structural support.
Rafters are not the same as roof trusses. Rafters are commonly assembled on site as part of a stick-framed roof. Trusses are engineered assemblies, usually made of interconnected members, that are manufactured to span between supports. Both approaches are widely used in U.S. residential construction, but they have different design and installation requirements.
Main Types Of Roof Rafters
Common Rafters
Common rafters are the basic, regularly spaced rafters in a conventional gable roof. They typically extend from the exterior wall to the ridge board, following the roof slope. Their length, spacing, and size are determined by the roof plan and structural requirements.
A ridge board provides a nailing surface where opposing rafters meet; it is not automatically a load-bearing beam. In many conventional roofs, opposing rafters and ceiling joists or rafter ties help resist outward forces at the walls. Where the roof design does not provide the required ties, an appropriately designed structural ridge beam or another engineered solution may be necessary.
Hip Rafters
A hip rafter runs diagonally from an outside corner of the building toward the roof’s ridge. It forms the sloping junction where two roof planes meet on the exterior side of a hip roof. Because jack rafters commonly connect to it, a hip rafter may collect loads from several framing members.
Hip roofs slope down on multiple sides rather than ending in vertical gable walls. Their framing usually includes common rafters, hip rafters, and hip jack rafters. The connections and member sizes need to suit the loads and span; a hip rafter should not be assumed to be interchangeable with a common rafter.
Valley Rafters
A valley rafter runs diagonally where two roof sections meet to form an inward angle. Valleys often appear where one roof intersects another, such as at an L-shaped house or a dormer. Common rafters from the adjoining roof planes terminate against or connect to the valley framing.
Valley framing can concentrate loads and create a detail that must manage water carefully. The structural design, roof sheathing, flashing, and roofing installation all matter. A valley’s framing member and its connections should be selected for the actual roof layout rather than judged by appearance alone.
Hip Jack Rafters
Hip jack rafters, often shortened to hip jacks, are shorter rafters that run from an exterior wall to a hip rafter. Their upper ends meet the hip instead of reaching the ridge. They vary in length because the diagonal hip changes their starting point along the roof.
Hip jacks help complete the roof plane on each side of a hip. Their cuts and connections must fit the roof geometry and the supporting hip rafter. On a roof plan, they are usually shown as a series of shorter members meeting the hip line.
Valley Jack Rafters
Valley jack rafters are short rafters that run from a ridge or another upper roof support down to a valley rafter. They fill in a roof plane beside the valley. Their lengths vary according to their location and the intersecting roof slopes.
Although the term resembles “hip jack,” the two members connect to different diagonal supports and serve opposite roof intersections: hip jacks meet a hip, while valley jacks meet a valley. Accurate layout is important because the roof planes must intersect cleanly.
Cripple Rafters
Cripple rafters are short framing members that do not run the full distance between a wall and the ridge. The term may describe short rafters used near hips, valleys, or other framing transitions, though usage can vary among regions and construction plans. Their specific role should be confirmed from the drawings rather than inferred from the label alone.
Flying Rafters
A flying rafter is a rafter that extends beyond the exterior wall to form a roof overhang. The projecting portion is often called the rafter tail. It supports the eave framing and provides a base for the roof edge, soffit, and fascia details.
Overhangs can help shield walls and windows from rain and sun, but their dimensions and connections must account for local wind exposure and the roof’s construction. A long projection may need additional support or a specifically designed connection.
Shed Or Mono-Pitch Rafters
Shed rafters, also called mono-pitch rafters, support a single-sloping roof plane. They span between a higher support and a lower support rather than meeting at a central ridge. This framing is common on sheds, additions, porches, and some contemporary homes.
The roof’s slope, clear span, and support conditions determine the rafter design. A shed roof attached to an existing house also needs carefully designed connections and flashing where the two structures meet.
Rafter Types Compared
| Rafter Type | Typical Location | What It Does |
|---|---|---|
| Common | Gable or roof plane | Runs from a wall to a ridge or other upper support |
| Hip | Outside roof corner | Forms the diagonal edge where roof planes meet |
| Valley | Inside roof intersection | Supports the junction between intersecting roof planes |
| Hip jack | Beside a hip | Runs from a wall to a hip rafter |
| Valley jack | Beside a valley | Runs from an upper support to a valley rafter |
| Flying | At the eave | Projects beyond a wall to form an overhang |
| Shed or mono-pitch | Single-slope roof | Spans between supports at different heights |
Rafters And Common Roof Shapes
The roof shape helps determine which rafters are needed. A simple gable roof generally uses common rafters on two sides, with gable end framing at each end. A hip roof adds hip rafters and hip jacks. A roof with intersecting wings or dormers may require valley rafters and valley jacks.
Some roofs combine several forms. For example, a house may have a main gable roof, a hip-roofed porch, and a small shed roof over an addition. The framing plan will identify the members and connections needed at each transition. Roof geometry can be complex even when the visible roofline appears simple.
How Rafter Dimensions And Spacing Are Determined
There is no single rafter size that is correct for every house. Designers and builders consider the clear span, rafter spacing, roof pitch, lumber species and grade, roof dead load, and applicable live loads. Snow, wind, and seismic requirements vary by location and building conditions.
In the United States, residential construction generally follows a locally adopted building code, often based on an edition of the International Residential Code (IRC). Local amendments and permitting requirements may differ. The IRC includes provisions and span tables for qualifying conditions, but those tables are not a universal substitute for checking the project’s design assumptions.
Rafter spacing is commonly laid out at regular intervals, such as 16 or 24 inches on center, but actual spacing depends on the design and materials. Wider spacing can affect the required rafter capacity and the sheathing selected. Roof pitch also affects rafter length and the geometry of cuts; it does not, by itself, establish a safe rafter size.
For unusual spans, heavy roofing, high snow loads, large openings, or complicated roof intersections, a building official or qualified design professional may require engineered calculations. Roof alterations deserve special care because removing or cutting a rafter can change how loads are carried.
Rafter Connections And Supporting Members
Rafters rely on sound connections as well as adequate member size. A birdsmouth cut, where permitted by the design, lets a rafter seat on a wall plate, but excessive cutting can weaken the member. Metal connectors, nails, screws, and other fasteners must be appropriate for the connection and installed as specified.
Rafter ties and ceiling joists can help resist the outward thrust that roof framing may place on exterior walls. Collar ties are typically installed higher in the roof to help resist separation of opposing rafters near the ridge under certain conditions. They are not automatically a replacement for rafter ties or a properly designed ridge beam.
Roof framing also depends on adequate bracing and support for beams, posts, walls, and foundations below. A roof member’s design cannot be evaluated in isolation from the structure that receives its loads.
Rafters Versus Roof Trusses
Stick-framed rafters offer flexibility for some roof shapes and can leave open space beneath the roof, depending on the design. They are often assembled piece by piece on site. Roof trusses, by contrast, are engineered for a specific layout and are commonly delivered as prefabricated units.
Trusses should not be cut, drilled, or altered without approval from the truss designer or manufacturer. Their internal web members are part of the engineered assembly. Similarly, changing a rafter or adding an opening to a roof requires an assessment of the structural design rather than a quick field adjustment.
Reading Rafter Terms On A Roof Plan
Roof plans may use abbreviations and conventions that vary by designer. Common rafters are often drawn as repeated lines, while hip and valley rafters appear as diagonal lines between roof planes. Jack rafters are shown connecting to those diagonal members. A framing plan, sections, notes, and connection details should be read together.
When reviewing a plan or discussing a repair, useful questions include:
- Which roof members are bearing on walls, beams, or other rafters?
- Are the diagonal members hips or valleys, and what supports them?
- What rafter size, grade, species, and spacing are specified?
- What connectors and bracing are required?
- Does the design account for local snow and wind conditions?
Safety And Repair Considerations
Signs such as a sagging roofline, cracked framing, water damage, or separated connections warrant prompt evaluation. Leaks can deteriorate roof sheathing and framing, while unapproved alterations can weaken load paths. A roofing contractor may identify visible problems, but structural concerns may call for a licensed engineer or another qualified professional.
Homeowners should avoid cutting, notching, or removing rafters to make room for ducts, skylights, or storage without an approved plan. A roof opening often requires headers and additional framing, and the correct solution depends on the member layout and loads. Permits may be required for structural work; local building departments can explain applicable rules.
Reliable Sources For Roof Framing Guidance
For code requirements, consult the building department in the project’s jurisdiction and the locally adopted residential code. The International Code Council publishes the IRC, although the edition adopted locally may differ. The American Wood Council provides wood-design resources, including guidance related to structural wood framing. Plans from a qualified design professional and manufacturer instructions for engineered products should take precedence for project-specific details.
Key takeaway: Common, hip, valley, jack, flying, and shed rafters describe different roles in a roof’s framing. Identifying the member is useful, but safe construction depends on the complete design: loads, spans, supports, connections, materials, and local code requirements.