6 Best Steel Gusset Plates for Custom Truss Fabrication

When a custom truss design falls outside the scope of standard catalog hardware, the structural integrity of the roof rests entirely on the gusset plates. Selecting the wrong gauge or material can lead to premature connection failure, truss sagging, or total system collapse under snow or wind loads. Proper fabrication requires matching the steel strength to the specific geometry of the load-bearing joints. This guide cuts through the noise to highlight the best steel plates for custom truss assembly in the field.

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Simpson Strong-Tie MP: Best for Accessibility

Simpson Strong-Tie MP (Multi-Purpose) plates are the industry standard for a reason: they are available at almost any lumber yard or building supplier. When a project hits a snag and extra bracing is needed on a Saturday morning, these plates provide a reliable, code-compliant solution.

These plates feature a strategic hole pattern designed to optimize fastener distribution without splitting the underlying lumber. They work exceptionally well for repair work or modifying existing trusses where space is limited and specialized fabrication is not an option.

While they are excellent for light-duty bracing and common DIY framing, do not rely on these for primary structural connections in high-load custom spans. Always check the load tables provided by the manufacturer to ensure the plate’s shear capacity meets the specific requirements of the roof pitch and tributary area.

Custom A36 Steel: For Pro-Level Fabrication

A36 is the workhorse of structural steel, offering a yield strength of 36,000 psi. When a truss requires a specific shape, size, or unique bolt pattern that off-the-shelf connectors cannot provide, ordering custom-cut A36 plates from a local steel fabricator is the preferred route.

The primary advantage here is complete control over dimensions and hole placement. Fabricators can plasma-cut plates to perfectly match the meeting angles of complex chords, ensuring that fasteners are centered properly to avoid edge-distance failures.

Remember that raw A36 steel will rust quickly if left exposed to the elements. Once the gussets are fabricated, they must be painted with a high-quality zinc-rich primer or powder-coated to prevent oxidation that can eventually weaken the connection.

USP TGS Gussets: For Hybrid Wood/Steel Trusses

USP (now part of MiTek) TGS gussets are engineered specifically for connecting timber members in heavy-duty or hybrid construction. These plates are ideal when mixing heavy timber trusses with steel tension rods or structural steel rafters.

The high-gauge thickness of these plates allows for the use of larger diameter lag screws or structural bolts, which are often necessary when dealing with heavy roof loads. Their design minimizes eccentricity in the joint, meaning the load paths are kept as linear as possible.

These are not intended for simple residential shed roofs; they are for serious structural work. If the project involves large-span designs or heavy snow zones, these plates provide the stiffness required to keep the wood members from rotating or twisting under stress.

G90 Galvanized Plates: Top Pick for Exterior Use

Corrosion resistance is non-negotiable when building open-air structures like pavilions, carports, or roof systems with significant overhangs. G90 galvanized steel offers a heavy-duty zinc coating that protects the base metal against moisture, humidity, and salt air.

Unlike standard painted steel, the G90 process provides a sacrificial layer that protects the plate even if the surface is scratched during installation. This makes them the superior choice for outdoor applications where maintenance access to the connection point will be difficult or impossible after the roofing material is installed.

Always be wary of using non-galvanized hardware in pressure-treated wood. The chemicals in treated lumber can accelerate corrosion on contact, making G90 or stainless steel mandatory for any plate directly touching treated timber.

Pre-Drilled Plates: Fastest for Simple Layouts

Pre-drilled plates are a massive time-saver for repetitive, simple truss assemblies. By eliminating the need to drill holes on-site, labor costs drop and the risk of misaligned bolts is significantly reduced.

These plates typically feature a standardized hole layout that matches common structural screw sizes. This is particularly helpful for contractors who use proprietary high-shear screws, as the hole diameter is usually pre-sized for a snug fit that prevents fastener wobble.

The trade-off is flexibility. If the truss geometry requires a slightly offset bolt pattern to avoid a knot in the wood, pre-drilled holes can become a liability. If the plate cannot be positioned perfectly, the entire joint strength may be compromised.

1/4″ Plate Stock: For Your Heaviest Load Jobs

When the engineering specs demand heavy-duty connection points for commercial-grade trusses, 1/4″ steel plate stock is the minimum baseline. This thickness provides the rigidity needed to act as a true gusset, preventing the steel itself from bending under high compression or tension forces.

Handling 1/4″ stock requires more than a standard drill press and a hand-held circular saw. It demands an oxy-acetylene torch or a professional-grade metal band saw for cutting, and carbide-tipped bits or magnetic drills for accurate hole boring.

Only use this weight of steel when a structural engineer has signed off on the plan. Using 1/4″ plate is often overkill for residential roofs and can actually make the joint too rigid, potentially transferring stresses elsewhere in the truss that the wood members may not be designed to handle.

Choosing Your Gusset Plate Steel and Thickness

• 12-16 Gauge: Standard for residential truss bracing and light structural connections.
• 3/16″ to 1/4″: Required for heavy-duty spans, commercial headers, and large timber-frame joints.
• A36 Steel: Use when custom shapes are required; verify that the steel is primed or galvanized.
• Stainless Steel: Mandatory for coastal environments or areas with persistent high humidity.

Fastener Guide: Bolts Screws and Weld Specs

The gusset plate is only as strong as the connection to the wood. Avoid standard carriage bolts if possible; structural grade lag screws or through-bolts with washers are far more reliable for resisting withdrawal forces.

When fastening, always stagger your bolt pattern. Placing bolts in a straight line along the grain creates a “zipper” effect that can split the truss member under load. A diamond or zig-zag pattern allows the wood fibers to distribute the stress more effectively.

If the specs call for welding, ensure the welder is certified for the material thickness. Field welding galvanized steel requires extra ventilation and specific techniques to avoid breathing toxic zinc fumes, and the welds themselves must be painted with cold-galvanizing compound immediately after cooling.

Nailing the Layout: Gusset Placement Best Bets

A gusset plate should be centered perfectly over the joint to ensure even load transfer across all connected members. If the plate is skewed, the truss will experience uneven tension, leading to potential warping over time.

Always leave a small gap between the wood members if the design requires it, ensuring the gusset is the bridge between them. Over-tightening fasteners can crush the wood fibers, reducing the effective bearing area of the joint.

Use a high-quality impact driver for screws, but finish the last few turns by hand. This prevents over-driving the head, which can strip the wood fibers and drastically reduce the withdrawal value of the connection.

Custom vs. Engineered Trusses: Know When to Build

Engineered trusses from a factory are produced with automated presses that embed plates with thousands of pounds of pressure, creating a bond that hand-driven bolts or screws cannot replicate. If the project involves long spans or complex roof shapes, factory-engineered trusses are almost always the safest and most cost-effective path.

Custom fabrication is best reserved for unique architectural features, repairs, or projects where the logistics of transporting large factory-built trusses are impossible. If a custom build is necessary, have the design reviewed by a licensed structural engineer.

A few hours of consultation with an engineer is a small price to pay to avoid a failing roof structure. Never substitute “rule of thumb” measurements for professional calculations when life safety and structural integrity are on the line.

The decision to use custom gusset plates is a move toward a more robust, specialized framing solution. By selecting the right steel gauge, coating, and fastener strategy, you ensure the connection remains as strong as the wood it supports. Always prioritize engineering guidance over convenience when structural loads are in play.