Roof trusses and rafters are the two main ways to frame a roof. Rafters are individual boards cut and built piece-by-piece on-site, while trusses are pre-engineered, factory-built triangular units delivered ready to install. Trusses cost less and span further, but rafters allow for usable attic space. [1, 2, 3, 4]
Design and Construction
- Rafters: Built "stick-by-stick" by carpenters on the job site using individual dimensional lumber leaning against a central ridge board.
- Trusses: Manufactured off-site in climate-controlled factories using smaller lumber pieces joined tightly together with metal connector plates. [2, 3, 5]
Cost and Labor
- Rafters: Higher overall cost due to intensive on-site labor and longer build times.
- Trusses: Lower overall cost; prefabricated design cuts down installation labor significantly, though they often require a crane to lift into place. [2, 6, 7, 8]
Span and Strength
- Rafters: Shorter span capacity (typically up to 24–30 feet) before needing interior load-bearing support walls.
- Trusses: Excellent engineering allows long spans (up to 60 feet) without intermediate interior supports, giving more layout freedom below. [1, 6, 7]
Attic Space and Flexibility
- Rafters: Leave the attic completely open and free of obstructions, making it ideal for future loft conversions, extra storage, or bonus rooms.
- Trusses: Internal web bracing fills the attic space completely, leaving little to no functional headroom or storage room. [1, 4]
A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof. Trusses usually occur at regular intervals, linked by longitudinal timbers such as purlins. The space between each truss is known as a bay.[1]
A rafter is one of a series of sloped structural members such as steel beams that extend from the ridge or hip to the wall plate, downslope perimeter or eave, and that are designed to support the roof shingles, roof deck, roof covering and its associated loads.[2]
Rafters VS Trusses: What Are The Pros And Cons Of Each? - YouTube
Trusses Vs. Rafters | How The Truss Ruined American Houses - YouTube
This video explores the evolution of American roof construction, arguing that while roof trusses have become the industry standard for their speed and cost-effectiveness, they have negatively impacted the design, usability, and long-term health of modern homes.
Roof Trusses vs. Rafters
- Roof Trusses (0:00 - 4:23): Developed in the 1950s using metal plates and hydraulic presses, trusses allow for fast assembly and wider spans without needing internal bearing walls. However, the complex interior 'webs' of a truss typically render attic space unusable and create 'out of sight, out of mind' areas prone to undetected issues like condensation and mold.
- Traditional Rafters (4:24 - 9:30): Hand-framed rafters require more time and skilled labor but offer significant advantages in design flexibility and usable living space (9:30 - 10:07). Without the dense web structure of a truss, attics can be converted into functional lofts, storage, or additional rooms.
The Impact on Housing
- Wasted Space: The speaker argues that approximately 75% of modern American homes use trusses, leading to massive, tall roof structures that contain entirely empty, wasted space (10:07 - 11:20).
- Proportions and Design: Trusses have contributed to modern homes having less desirable proportions compared to older homes that utilized attic space through steep pitches or dormers (11:20 - 13:25).
- Health and Maintenance: The speaker advocates for designs that allow for easier inspection of the home's structure (like vaulted ceilings), suggesting that closed-off, unused attics are a recipe for mold and maintenance neglect (14:15 - 15:26).
