Types of Rafters Used in Residential Construction

In residential construction, the roof is one of the most critical components, providing protection from the elements and contributing significantly to the structural integrity and aesthetic appeal of a home. At the core of any roof system are rafters—sloped structural members that support the roof deck and its loads. Understanding the various types of rafters used in residential construction is essential for architects, builders, and homeowners alike. This article explores the different types of rafters, their functions, applications, and benefits.

What Are Rafters?

Rafters are inclined beams that run from the ridge or peak of the roof down to the exterior walls. They serve as a framework to support the roofing material, insulation, and ceiling below. Rafters work together with other structural components like ridge boards, purlins, collar ties, and ceiling joists to form a stable and durable roof system.

Traditionally made from wood, rafters can also be fabricated from steel or engineered wood products depending on design requirements and budget. Their shapes and configurations vary based on roof style, span length, load requirements, and architectural aesthetics.

Importance of Selecting the Right Rafters

Choosing appropriate rafter types affects not only the strength of the roof but also construction costs, ease of installation, ventilation options, and potential future modifications such as attic conversions or solar panel installations. Incorrect rafter selection can lead to structural failures, excessive deflection, or inefficient use of materials.

Common Types of Rafters in Residential Construction

Below are some of the most common types of rafters used in building residential roofs:

1. Common Rafters

Definition:
Common rafters are the standard rafters that run from the top plate of an exterior wall to the ridge board at the peak of the roof.

Description:
They are uniformly spaced and carry the main load of the roof covering. These rafters are typically cut to length based on the pitch (angle) of the roof and the span between walls. They form the basic framework for most pitched roofs such as gable or hip roofs.

Application:
Used in nearly all conventional pitched roofs where a simple sloping roof is desired.

Advantages:
– Easy to design and install
– Cost-effective for typical span lengths
– Good for straightforward roof plans

2. Jack Rafters (or Valley/Gable Rafters)

Definition:
Jack rafters are shorter rafters that do not extend all the way from the ridge board to wall plates but instead connect to other primary rafters like hip or valley rafters.

Description:
They are used around complex parts of roofs such as hips (external corners) and valleys (internal corners). Jack rafters fill in spaces between common rafters and hip or valley rafters to complete roof framing.

Types:
– Hip Jack Rafters: Extend from hip rafter down to wall plate.
– Valley Jack Rafters: Extend from valley rafter up to ridge board or plate.

Application:
Used in hip roofs, valley roofs, and other complex multi-directional roof designs.

Advantages:
– Allows for complex roof shapes
– Distributes loads effectively around corners

3. Hip Rafters

Definition:
Hip rafters run diagonally from an exterior corner (where two walls meet) up to the ridge board.

Description:
Hip rafters form the external angle where two sloping sides meet on a hip roof. They carry loads from jack rafters attached to them.

Application:
Found in hip roofs which slope on all sides without vertical ends.

Advantages:
– Adds strength at corners
– Supports complex roofing geometry

4. Valley Rafters

Definition:
Valley rafters run diagonally inside a roof where two sloping sections meet inwardly forming a valley.

Description:
Valley rafters support loads where water drainage collects along valleys. They carry jack rafters extending toward them.

Application:
Used wherever multiple roof sections intersect creating internal angles—common in cross-gabled or L-shaped homes.

Advantages:
– Provides robust support at internal corners
– Essential for water drainage management

5. Raised Heel Rafters

Definition:
Raised heel rafters have an extended heel end that provides additional space at the eaves for thicker insulation.

Description:
The “heel” is elevated compared to conventional common rafters allowing more room between top wall plate and bottom surface of rafter for insulation without compressing it.

Application:
Increasingly popular in energy-efficient home designs requiring high R-values at eaves while preventing thermal bridging.

Advantages:
– Allows thicker insulation at eaves without raising roof pitch or lowering ceiling height
– Improves energy efficiency significantly

6. Lookout Rafters

Definition:
Lookout rafters extend beyond exterior walls to support eaves overhangs.

Description:
They cantilever outward beyond wall line providing structural support for soffits and overhanging portions of roofs like porches or bay windows.

Application:
Commonly used where wide eaves are desired for shading or aesthetic reasons.

Advantages:
– Supports larger overhangs without additional posts or beams
– Helps protect walls from weather damage

7. Scissor Rafters

Definition:
Scissor rafters are paired angled members that cross each other forming an “X” shape resembling scissors when viewed from below.

Description:
They create vaulted ceilings inside while maintaining structural integrity by resisting spreading forces typical in simple common rafter systems without collar ties.

Application:
Used when vaulted or cathedral ceilings with exposed woodwork are desired in residences.

Advantages:
– Creates spacious interior ceiling volume
– Combines structure with aesthetic appeal

8. Collar Tie Rafters

Although technically collar ties are horizontal members rather than inclined rafters, they play an important role alongside common rafters by connecting two opposing rafters midspan near their upper part to resist spreading forces caused by roof loads.

Factors Influencing Rafter Selection

When selecting a type of rafter for residential construction, several factors come into play:

Roof Design & Complexity

Simple gable roofs typically use common rafters exclusively while more intricate designs like cross-gables, hips, dormers require jack, hip, valley rafters accordingly.

Span & Load Requirements

Longer spans with heavy roofing materials may require engineered wood or steel rafters versus standard dimensional lumber common rafters.

Energy Efficiency Goals

Homes seeking high thermal performance often use raised heel rafters to enable thick continuous insulation at eaves reducing heat loss significantly.

Aesthetic Preferences

Vaulted ceilings favor scissor trusses or open collar tie systems over traditional flat ceiling framed common rafter pairs.

Materials Used for Rafters

While traditional residential framing mostly relies on dimensional lumber, modern construction increasingly incorporates:

• Engineered Wood Products (LVL, Glulam): Stronger longer spans with less deflection.
• Steel Rafters: Used in custom homes needing long spans without intermediate support.
• Composite Materials: For specialty applications requiring moisture resistance or unique architectural forms.

Conclusion

Rafters are fundamental components shaping both form and function of residential roofs. From basic common rafters forming traditional pitched roofs to specialized jack, valley, hip, raised heel, scissor configurations addressing complex structures and performance goals—each type has its place depending on design intent and structural needs. Proper understanding helps ensure safe construction practices while optimizing comfort, durability, energy efficiency, and aesthetics in residential buildings. Whether you’re a homeowner planning a new build or renovation or a professional architect/builder managing projects—knowing your rafter types is key to successful roofing outcomes.