12.5 Engineered Wood, Trusses & Connectors

Where Field Judgment Gets Expensive

Quick Answer: Engineered wood, trusses, and connectors all share one rule: they perform only as the manufacturer's listing and the structural drawings specify. A cut truss chord, a substituted fastener, or a missed nailing pattern converts an engineered assembly into an unengineered one.

Carpentry is 12 of 100 items on the AZ ROC commercial outline and 17 of 100 on the residential outline. Section 12.1 covered conventional framing. This section covers the manufactured components that now do most of the structural work on both commercial and residential projects — and the field errors around them that generate correction notices, warranty claims, and ROC complaints.

Engineered Wood Products

Two properties matter in the field:

1. They are proprietary. Allowable spans come from the manufacturer's tables for that exact product, not from the IRC sawn-lumber span tables. Substituting "an equivalent LVL" without checking the table is a substitution the general contractor owns.
2. They tolerate very little field modification. An I-joist flange may never be cut, notched, or drilled — the flange carries the bending force. The web may be penetrated only at locations and sizes shown on the manufacturer's hole chart, which typically prohibits holes near bearing points. Cutting a 4-inch duct hole through an I-joist flange to run a bath fan is a structural failure that looks like nothing at the time.

Glulam orientation is another quiet trap: a glulam beam is manufactured with a stronger tension lamination on one face, usually stamped TOP. Installed upside down, its capacity drops substantially.

Trusses: Handling, Erection, and the No-Cut Rule

Trusses arrive engineered as a system. The general contractor's job is to keep them that way.

Handling and storage. Trusses are strong in their plane and weak out of it. They are lifted at the panel points shown on the delivery instructions — long-span trusses with a spreader bar — and stored on level blocking, upright or flat as directed, protected from standing water.

The no-cut rule. A truss chord or web may not be cut, notched, drilled, or otherwise modified in the field. If a duct, beam pocket, or attic access must pass through, the truss designer issues a written repair detail that specifies the reinforcement. This is not a formality: the members are sized with almost no reserve, and a cut web changes the load path through the entire truss.

Bracing has three distinct parts, and confusing them is what puts trusses on the ground:

Nearly every truss collapse during construction traces to inadequate temporary bracing — the crew set trusses, went to lunch, and the wind arrived. Temporary bracing is the erector's responsibility and is specified in the industry's bracing guidance, not on the architectural drawings.

Bearing and uplift. Trusses must bear the full width shown on the truss drawing, and they must be connected for uplift with the specified hurricane or truss clip. Toe-nailing where a clip was specified is a substitution with no rated capacity behind it.

Connectors and Their Fasteners

Metal connectors — joist hangers, hurricane ties, straps, post caps and bases, hold-downs — are tested assemblies. The published capacity applies only when the connector is installed with the specified fastener, in every hole, into the specified member.

That last row is a real Arizona issue on patio covers, ramadas, and any ground-contact framing: standard connectors in contact with ACQ-type treated lumber corrode, and the specification calls for hot-dip galvanized or stainless steel connectors and fasteners.

Shear Walls and the Load Path

A shear wall resists lateral load — wind and seismic — and it works only as a complete chain:

1. Sheathing of the specified thickness and grade.
2. Nailing pattern — the size, spacing at panel edges, and spacing in the field, all called out on the structural drawings.
3. Blocking at all panel edges where required.
4. Chords and hold-downs at the wall ends to resist overturning.
5. Anchor bolts or straps connecting the wall to the foundation.

Two field errors dominate:

• Overdriven nails. A pneumatic nailer set too hot drives nail heads through the face veneer of the sheathing. A nail head that breaks the surface no longer develops its rated shear value, and inspectors reject overdriven nailing on sight. Set the tool, check the first panel, and check it again after the compressor warms.
• Missing hold-downs. A shear wall without its hold-downs simply rotates. Hold-down anchors must be placed before the slab pour or installed as the epoxy anchors the detail specifies, at the exact location shown — not "close enough" to the corner.

Exam tip: questions in this area almost always describe a substitution and ask for its consequence. The correct answer is nearly always that the rated or engineered capacity no longer applies, and that the fix requires the designer's written direction rather than the crew's judgment.