Rafter
![]() |
A rafter is a structural component that is used as part of a roof construction. Typically, it runs from the ridge or hip of the roof to the wall plate of the external wall. Rafters are generally laid in series, side by side, providing a base to support roof decks, roof coverings and so on.
Rafters are typically made of timber or steel and can be concealed within the roof structure, or can be left exposed to the spaces below. The may have battens laid on top of and perpendicular to them, to fix the roof covering to.
Rafters can be used as a key component of various types of roof design. The couple roof comprises two rafters leaning against each other, tied where they meet at the top. The rafters sit on a wall plate which is an efficient means of spreading the load exerted by the roof structure down through the walls without creating pressure points where each rafter meets the wall.
A closed couple roof adds ceiling joists running horizontally between the rafter feet, to support a ceiling and to make the structure much more rigid.
In order to increase potential roof spans without compromising wall stability, increasing rafter sizes or attracting extra costs, purlins were introduced. These run perpendicular to rafters, providing additional stiffness. By installing a purlin into the roof structure, rafters no longer needed to be as thick and heavy, allowing larger potential spans.
In modern house construction, the most common form of rafter is known as the fink or 'w' trussed rafter. This consists of a rafter incorporating tension and compression members in the shape of a W. This is capable of spans up to 12 m and can be designed to accommodate many different pitch angles.
For more information see: Trussed rafters
The most common types of rafter include:
- Principal rafter: Usually the largest type of rafter located at the ends of a roof structure.
- Common rafter: Smaller rafters located in between the principals at both ends.
- Auxiliary rafter: Less common but can be used to support and reinforce a principal rafter.
- Compass rafter: Curved or bowed at the top or at both the top and bottom surfaces.
- Curb rafter: The upper rafters in a gambrel or Mansard roof.
- Hip rafter: Smaller rafters used for the corners of a hip roof.
- King rafter: On the side of a hip roof, a king rafter is the longest and is in line with the ridge.
- Valley rafter: The main rafter that is found at the lowest point of a valley roof.
- Jack rafter: A rafter that is shortened by landing on a hip rafter or being interrupted by a dormer window.
- Barge rafter: On a gable end this is the outermost rafter and is sometimes used to form a roof overhang.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Professional practical experience for Architects in training
The long process to transform the nature of education and professional practical experience in the Architecture profession following recent reports.
A people-first approach to retrofit
Moving away from the destructive paradigm of fabric-first.
International Electrician Day, 10 June 2025
Celebrating the role of electrical engineers from André-Marie Amperè, today and for the future.
New guide for clients launched at Houses of Parliament
'There has never been a more important time for clients to step up and ...ask the right questions'
The impact of recycled slate tiles
Innovation across the decades.
EPC changes for existing buildings
Changes and their context as the new RdSAP methodology comes into use from 15 June.
Skills England publishes Sector skills needs assessments
Priority areas relating to the built environment highlighted and described in brief.
BSRIA HVAC Market Watch - May 2025 Edition
Heat Pump Market Outlook: Policy, Performance & Refrigerant Trends for 2025–2028.
Committing to EDI in construction with CIOB
Built Environment professional bodies deepen commitment to EDI with two new signatories: CIAT and CICES.
Government Grenfell progress report at a glance
Line by line recomendation overview, with links to more details.
An engaging and lively review of his professional life.
Sustainable heating for listed buildings
A problem that needs to be approached intelligently.
50th Golden anniversary ECA Edmundson apprentice award
Deadline for entries has been extended to Friday 27 June, so don't miss out!
CIAT at the London Festival of Architecture
Designing for Everyone: Breaking Barriers in Inclusive Architecture.
Mixed reactions to apprenticeship and skills reform 2025
A 'welcome shift' for some and a 'backwards step' for others.