Trusses are a cornerstone of modern construction, known for their ability to efficiently support structures while maintaining strength and versatility. These pre-engineered frameworks, composed of interconnected elements forming triangular units, are commonly used in roofs, floors, and bridges. Trusses provide superior structural stability, allowing builders to span large distances without the need for additional supports, reducing material usage and installation time.
Trusses can be precision-engineered off-site and delivered ready for installation, ensuring consistent quality while reducing on-site labor and material waste. Their design flexibility accommodates everything from simple gable roofs to intricate rooflines with vaulted ceilings.
Types of Trusses and Styles
1. Common Trusses
These standard trusses are used in residential and commercial construction due to their simplicity, efficiency, and cost-effectiveness.
King Post Truss
- Design: A simple triangular shape with a central vertical post connecting the peak to the bottom chord.
- Best for: Small spans, such as sheds, porches, and residential roof structures.
- Span Range: Up to 16 feet.
Queen Post Truss
- Design: Similar to the King Post but with two vertical posts connected by a horizontal member for added stability.
- Best for: Moderate spans in residential and light commercial buildings.
- Span Range: 18-30 feet.
Fink Truss
- Design: Features a “W” shaped webbing, providing excellent load distribution.
- Best for: Steep-pitched roofs in residential homes, garages, and barns.
- Span Range: 16-33 feet.
Howe Truss
- Design: Diagonal members slant inward toward the center, with vertical posts providing support.
- Best for: Roofs and bridges where heavy loads require extra support.
- Span Range: 24-36 feet.
Pratt Truss
- Design: Features vertical members in compression and diagonal members in tension.
- Best for: Long spans in bridges and industrial buildings due to its material efficiency.
- Span Range: 30-60 feet.
- Warren Truss
- Design: Alternating diagonal members form a series of equilateral triangles.
- Best for: Bridges and roofs requiring uniform load distribution.
- Span Range: 30-80 feet.
2. Architectural and Specialty Trusses
These trusses enhance aesthetics and accommodate unique building designs.
Scissor Truss
- Design: Bottom chords angle upward to meet at the center, creating a vaulted ceiling effect.
- Best for: Homes, churches, and open-concept commercial spaces.
- Span Range: Up to 60 feet.
Attic Truss
- Design: Incorporates a large open space within the truss, allowing for a livable attic area.
- Best for: Maximizing usable space in residential homes.
- Span Range: Up to 80 feet.
Gambrel Truss
- Design: Features two different slopes on each side, resembling a barn-style roof.
- Best for: Barns, storage facilities, and homes with classic aesthetics.
- Span Range: 40-80 feet.
Vault Truss
- Design: Used for barrel or vaulted ceilings with two or three bearing points.
- Best for: High-end architectural designs in homes, churches, and commercial buildings.
3. Structural and Load-Bearing Trusses
These trusses provide strong support for large-scale construction projects.
Flat Truss
- Design: Horizontal top and bottom chords, making it ideal for flat or low-slope roofs.
- Best for: Warehouses, commercial buildings, and apartment complexes.
- Span Range: 20-100 feet.
Mono Truss
- Design: A single-sloped truss, often used in shed-style roofs.
- Best for: Additions, porches, and buildings with asymmetrical roof designs.
- Span Range: 20-50 feet.
Piggyback Truss
- Design: A two-part truss where the upper portion is placed on top of a lower section for ease of transport.
- Best for: Large-span buildings where full-height trusses are difficult to ship.
- Span Range: 40-100 feet.
Double Cantilever Truss
- Design: Extends beyond its supports, allowing for overhangs on both sides.
- Best for: Bridges, balconies, and long-span commercial projects.
4. Custom and Hybrid Trusses
These trusses combine different designs for specific architectural or structural needs.
Valley Set Truss
- Design: Installed over an existing truss to create complex roof shapes and transitions.
- Best for: Roof designs with intersecting planes or dormers.
Parallel Chord Truss
- Design: Both top and bottom chords run parallel, often used in floor systems.
- Best for: Multi-story buildings requiring strong yet lightweight floor support.
Modified Queen Truss
- Design: Similar to the Queen Post but with additional webbing to accommodate larger spans.
- Best for: Roofs with heavier loads or increased structural demands.
- Span Range: 32-44 feet.
Common Truss Shapes
Trusses can be designed in various shapes to match architectural preferences and structural requirements:
- Common Truss: Basic triangular shape, cost-effective for most applications.
- Hip Truss: Provides a sloped end for hip-style roofs.
- Mono Scissors Truss: A combination of mono and scissor trusses for asymmetrical vaulted ceilings.
- Stepdown Hip: Used for multi-tiered roofs.
- Clear Story Truss: Creates high windows for natural lighting.
- Cathedral Truss: Forms an arched ceiling effect, popular in churches and open-concept homes.
- Sloping Flat Truss: Used for buildings needing a gentle roof slope.
How Trusses Work
Trusses leverage triangular geometry to efficiently distribute tension and compression forces, transferring loads to their support points. The top chords are typically under compression, while the bottom chords handle tension. Internal web members connect these chords, ensuring structural integrity.
For example:
- Roof Trusses: Span wide areas, reducing the need for interior load-bearing walls.
- Floor Trusses: Include open spaces for HVAC, plumbing, and electrical systems, simplifying installations.
Trusses are engineered to handle various environmental loads, such as snow and wind, ensuring long-term durability and stability.
Materials Used in Trusses
Trusses are crafted from several materials, each with unique benefits:
- Wood: Common in residential construction due to cost efficiency and ease of customization.
- Engineered Wood: Includes laminated veneer lumber (LVL) and glulam for enhanced strength and precision.
- Steel: Preferred for industrial or commercial projects requiring fire resistance and high load capacities.
Installation and Bracing
Proper installation and bracing are essential for truss performance. Temporary bracing stabilizes the structure during erection, while permanent bracing integrates it into the overall building system. Key steps include:
- Aligning trusses straight and plumb.
- Securing diagonal and lateral bracing to prevent movement.
Bracing ensures safety and maintains the structural integrity of the system throughout its lifespan.
Trusses Versus Other Framing Systems
Trusses can provide significant advantages over other framing methods, including stick framing, timber framing, and engineered wood products (EWP). The right choice depends on factors like budget, structural requirements, and ease of installation. Below is a comparison of the key framing systems:
Stick Framing (Traditional Hand-Built Framing)
Pros:
- Lower material costs (in some cases).
- Good for small or custom-built projects.
Cons:
- Requires skilled labor, increasing installation time and costs.
- Generates significant material waste due to on-site cutting.
- Limited span capability, often requiring interior load-bearing walls.
Timber Framing (Post and Beam Construction)
Pros:
- Aesthetic appeal with exposed wood beams.
- Provides excellent durability.
Cons:
- Slow to install, requiring specialized craftsmanship.
- Expensive due to the use of large timber sections.
- Difficult to run utilities (electrical, plumbing, HVAC).
Engineered Wood Products (EWP)
Pros:
- Includes I-Joists, Glulam Beams, and LVL (Laminated Veneer Lumber).
- Stronger and more consistent than traditional lumber.
- Can be trimmed to fit irregular spaces, unlike prefabricated trusses.
Cons:
- Limited use in complex roof designs.
- Some products require special connections for installation.
- Not as cost-effective as trusses for large spans.
Wood Trusses (Metal Plate Connected Wood Trusses)
Pros:
- Highly cost-effective due to prefabrication.
- Fast installation, reducing labor costs.
- Capable of spanning up to 90 feet without intermediate supports.
- Open web design allows easy installation of plumbing, electrical, and HVAC.
Cons:
- Requires a truss placement plan before installation.
- Limited on-site modifications, unlike stick framing.
Steel Trusses (Cold-Formed Light Gauge Steel)
Pros:
- Lighter than wood while maintaining high strength.
- Excellent fire resistance, ideal for commercial/industrial buildings.
- Consistent quality, free from warping or shrinkage.
Cons:
- More expensive than wood trusses upfront.
- Requires specialized fasteners and connectors.
- May need thermal insulation to prevent condensation.
Applications of Trusses
Trusses are widely used in:
- Residential Construction: Supporting various roof shapes like gable and hip roofs.
- Commercial Buildings: Large-span designs for warehouses and shopping centers.
- Bridges: Heavy-duty trusses like Warren or Pratt for long-distance spans.
- Agricultural Structures: Barns and greenhouses for robust and affordable roofing solutions.
Custom Truss Design Options
Trusses can be tailored to meet specific needs, such as:
- Hurricane Resistance: Engineered to withstand high wind loads.
- Snow Loads: Reinforced designs for areas with heavy snowfall.
- Architectural Appeal: Vaulted or tray ceilings enhance aesthetics and functionality.
FAQs About Trusses
Why are trusses triangular?
Triangles distribute forces evenly, ensuring stability without deformation.
Can trusses be customized?
Yes, trusses are engineered for specific spans, loads, and architectural needs.
How do trusses compare to rafters?
Trusses are pre-engineered, cost-effective, and faster to install, while rafters require more labor and customization.
What is the lifespan of a truss?
Properly designed and installed trusses can last decades, provided they are well-maintained.