Star plates, also known as joist hanger plates or gang-nail connector plates, are stamped metal plates used to connect wood framing members at critical joints. Despite their simple appearance, these connectors play a significant role in the structural integrity of modern light-frame construction. This guide covers the different types of star plates, their load-rated applications, proper installation procedures, and how to identify them on existing structures.
What Are Star Plates?
Star plates are galvanized steel plates with integral teeth or prongs that are pressed into wood members to create a strong mechanical connection. The name derives from the starburst pattern of teeth that radiates from the center of the plate. These connectors are manufactured by cold-stamping 16-gauge to 20-gauge galvanized steel sheet, which produces the teeth and simultaneously forms them at right angles to the plate surface.
The plates function by embedding their teeth into adjoining wood members, creating a connection that resists both tension and shear forces. Unlike nails or screws that fasten through one member into another, star plates provide surface-level grip across a broad area, distributing loads more evenly.
| Star Plate Type | Typical Dimensions | Gauge (Steel Thickness) | Primary Application |
|---|---|---|---|
| Standard truss plate | 3 in × 5 in | 18 ga (0.048 in) | Pre-engineered roof trusses |
| Heavy-duty plate | 4 in × 8 in | 16 ga (0.060 in) | Floor trusses, beam connections |
| Mini connector | 1.5 in × 3 in | 20 ga (0.036 in) | Light framing, bracing |
| Gusset plate | 6 in × 6 in or larger | 14 ga (0.075 in) | Structural splice connections |
Historical Context
Star plates emerged in the mid-20th century alongside the development of engineered wood trusses. Before their introduction, wood truss joints were connected with plywood gusset plates glued and nailed in place. The pressed-metal connector plate drastically simplified truss manufacturing, enabling the growth of the pre-fabricated truss industry. By the 1970s, essentially all factory-built roof trusses used metal connector plates. Today, the structural Building Components Association reports that over 80 percent of residential roof structures in the United States utilize metal-plate-connected trusses.
Applications in Modern Construction
Roof Trusses
The most common application for star plates is in pre-engineered roof trusses. At each joint where web members meet chords, truss plates transfer tensile and compressive loads between members. The design of each plate location is calculated by truss design software, which specifies the exact plate size, orientation, and number of teeth required to handle the design loads.
Floor Trusses
Floor trusses use larger heavy-duty plates because the loads are generally greater than in roof applications. The plates connect the top and bottom chords to diagonal web members, creating a lightweight but strong floor framing system that can span up to 30 feet or more without intermediate bearing walls.
Retrofit and Repair
Star plates are also used in retrofit applications where existing connections need reinforcement. Splice plates can repair damaged truss members, and mini connectors can strengthen loose or undersized joints in existing framing. Building inspectors often require star-plate reinforcement when modifying load-bearing walls or cutting into existing trusses for roof penetrations.
Installation Requirements
Proper installation of star plates is critical to their structural performance. Manufacturer specifications and building codes mandate specific requirements:
- Press force: The plates must be pressed into the wood using a hydraulic or pneumatic press that delivers the manufacturer’s specified force (typically 2,000 to 8,000 pounds). Hammering is not acceptable because it cannot deliver uniform penetration.
- Tooth embedment: Teeth must be fully embedded so the plate surface contacts the wood. Partial embedment reduces load capacity by up to 50 percent.
- Wood moisture content: Truss plates should be installed in wood with a moisture content between 12 and 18 percent. Overly dry wood can crack during pressing; overly wet wood may not provide adequate tooth grip.
- Plate alignment: The plate must be centered on the joint line with equal coverage on both connecting members. Off-center installation creates eccentric loading that can cause joint failure.
Load Capacity Data
| Plate Size | Tooth Count | Allowable Tension (lb) | Allowable Shear (lb) |
|---|---|---|---|
| 3 in × 5 in | 24 | 1,200 | 1,800 |
| 4 in × 5 in | 32 | 1,600 | 2,400 |
| 4 in × 8 in | 52 | 2,600 | 3,900 |
| 6 in × 6 in | 60 | 3,000 | 4,500 |
Identification of Existing Star Plates
When working on an existing building, identifying the star plates in trusses helps determine load paths and assess structural modifications. Look for the galvanized steel plates at every truss joint. Each plate typically carries a manufacturer stamp or code that can be traced back to engineering specifications. The absence of plates at a joint that appears to be a truss connection may indicate a field repair or a non-engineered modification.
If you are cutting or drilling into a truss for a roof window, skylight, or mechanical penetration, avoid cutting through or near connector plates. Even a single severed plate tooth can reduce the joint capacity significantly. Many professional truss repair kits include star plates specifically designed to reinforce trusses that have been altered or damaged.
Corrosion Protection
Standard star plates are galvanized for corrosion resistance suitable for dry interior conditions. For exterior applications, pressure-treated wood connections, or high-humidity environments, stainless steel or heavily galvanized plates should be specified. The corrosion rate of standard galvanized plates in interior service is negligible, but in coastal environments or where the wood preservative chemicals are corrosive, the plate life can be significantly shorter.
Understanding star plates is essential for anyone involved in wood frame construction. These simple pressed-metal connectors enable the efficient, cost-effective, and structurally sound truss systems that form the backbone of most residential and light-commercial construction today.