A wood roof truss turns a pile of lumber into a structural system that carries snow, wind, and its own weight across spans that would sag under conventional stick framing. Erection is where that system comes together, and it is also where most mistakes happen, because a truss is strong in place and fragile on its side. The same planning discipline that governs erection of a balanced cantilever bridge applies at a smaller scale: know the loads, plan the lift, and control every piece until it is braced.
Plan the Lift Before the Trusses Arrive
Truss erection starts on the ground, days before the crane arrives. Confirm the delivery date, the truck size, and where the bundles will be staged. Check the ground conditions where the crane will sit and where the crew will work; soft ground needs mats or plates, and a slope changes the crane’s capacity. Confirm the truss drawings against the building plans, because an error found at the plant is a phone call, while an error found in the air is a problem. Work through the pre-arrival checklist:
- Verify truss quantities, sizes, and on-center spacing against the plans.
- Confirm the delivery truck can reach the staging area without overhead obstructions.
- Mark underground utilities before any heavy equipment moves in.
- Compact and level the crane pad, and add mats if the soil is soft.
- Assign a spotter whose only job is watching the landing zone.
Site prep and crane placement
The crane should be set where it can reach the far end of the roof at the required radius without moving. The crane operator needs a written lift plan that lists each truss weight, the pick points, and the load path, and the crew needs a spotter with a clear view of the landing zone. Keep the area under the boom clear of tools, materials, and people, and establish a hand-signal or radio routine before the first lift.
Staging trusses for the crew
Keep bundles flat and dry, off the ground on blocks, and sorted so the crew can grab trusses in erection order. Inspect each truss for damage during unloading: cracked chords, loose plates, and bent webs travel poorly and should be flagged before they are lifted. The lifting plan matters as much for a 40-foot truss as it does for tilt-up concrete panel erection: every panel and every truss needs a known pick point, a clear path, and a spotter who can see the landing zone.
Know Your Truss Types and Their Limits
Trusses are engineered assemblies, and each shape has a purpose and a span range. The webs and chords work together as triangles, which makes the truss stiff in its own plane and unstable out of it. That distinction drives everything about handling: a truss can carry its design load once it is upright and braced, but the same truss can snap under its own weight if it is picked at the wrong points or rolled on its side.
Common shapes and what they do
The oldest shapes still earn their keep. The king post truss versus queen post truss comparison shows how a single central post handles short spans while two posts with a collar beam extend the reach. Modern residential roofs lean on fink trusses, which form the familiar W pattern and cover most house widths, with scissors for vaulted ceilings and attic trusses when the roof needs to contain a room. The table summarizes the common types:
| Truss type | Typical span | Common use |
|---|---|---|
| King post | Up to 24 ft | Sheds, small roofs, gable ends |
| Queen post | 24-45 ft | Medium spans, simple gables |
| Fink (W) | 20-60 ft | Most residential roofs |
| Scissor | 20-50 ft | Vaulted ceilings |
| Attic | 20-40 ft | Rooms in the roof |
Reading the truss drawing
The truss design drawing (TDD) is the contract for each piece. It lists the grade and species of lumber, the plate sizes, the bearing points, the on-center spacing, and the bracing requirements. The crew should read it before the first lift, because the bracing plan on the drawing is often the difference between a safe roof and a collapse waiting for wind.
Choose the Right Lifting Equipment
The crane must match the heaviest truss at the farthest reach, and that calculation includes the rigging, not just the truss. A 30-foot fink truss can weigh several hundred pounds, and long spans multiply the load. When in doubt, the crew sizes up, because lifting capacity falls as the boom extends and the radius grows.
Sizing the crane
The lift plan starts with the load chart: truss weight plus rigging, at the required radius, with a safety margin. The operator checks the chart for the exact boom length and angle before the lift. Telehandlers and boom trucks handle smaller residential trusses, while long-span or heavy commercial trusses call for a conventional crane. Residential crews borrow the same philosophy that guides specialized machinery for bridge erection: the machine is matched to the lift, not the other way around.
Rigging and tag lines
Nylon slings or spreader bars protect the lumber from chafing, and tag lines let the ground crew steer the truss without reaching into the landing zone. Never wrap a chain directly around a chord, and never stand under a suspended load. Run the rigging checks before every lift:
- Inspect slings for cuts, abrasions, and damaged eyes.
- Confirm the spreader bar is rated for the truss width.
- Check that the tag line is clear of the load path.
- Verify the load chart matches the boom length and radius.
- Re-check the weather, because wind moves both the load and the crew.
Set, Align, and Brace Every Truss
Erection follows a sequence that protects the crew and the structure. The first two trusses get temporary bracing to make a stable bay, and every truss after that is connected and braced before the crew leaves it. Bracing is not optional trim; it is the system that keeps the trusses vertical under their own weight and the wind that arrives before the sheathing.
The erection sequence
- Set the first truss, plumb it, and brace it to temporary supports at each end.
- Set the second truss, space it correctly, and connect the top chords with temporary lateral bracing.
- Install the permanent bracing shown on the truss drawings, including web bracing where specified.
- Nail each truss to the top plate with the pattern called out on the plans, and check the spacing as you go.
- Verify alignment of the ridge and the bearing points before sheathing starts, and correct any bowed trusses with straightening bracing.
Bracing rules
Temporary bracing restrains the compression chords and keeps the assembly square; permanent bracing, often shown on the TDD as a bracing plan, stays in the finished roof. Never remove temporary bracing until the permanent system is in place. Quality control follows the pattern used in steel bridge design and construction: fabrication tolerances, erection sequences, and inspection all matter, and a misaligned connection found early costs a fraction of one found after the deck is on.
Follow Safety Rules on the Roof Deck
Roof framing is one of the highest fall-risk jobs on a site, and the rules exist because the consequences are permanent. Harnesses attached to a rated anchor, guardrails at the open edges, and a clean deck with no loose tools underfoot are the baseline. The crew walks only on braced trusses and sheathed areas, never on unbraced members, and the weather decides the schedule: wind over roughly 20 mph moves trusses sideways and lifts sheathing, so the crew stops the lift at the first gust that feels wrong.
Communication and control
One person gives the signals, the operator obeys only that person, and everyone repeats the call back on a noisy site. The pre-lift meeting covers the load, the path, and the landing zone before the first truss leaves the ground. Crane crews run the same drill on residential roofs as on big jobs; the procedures behind all-terrain crane operations for precast concrete erection transfer directly: a pre-lift meeting, load charts, and a supervisor who stops the lift at the first sign of trouble.
Sequence the Work to Keep the Crew Moving
A roof goes up fastest when every crew member has a fixed job: one sets the truss at the bearing, one plumbs and nails, one runs the bracing, and the ground crew keeps the next truss ready at the staging pile. Sheathing should follow the bracing as soon as the bay is square, because sheathing locks the assembly rigid and gives the crew a safe deck to work from.
Deliveries and weather windows
Schedule deliveries so the crew never waits on material and the site never stores more than it can protect. Watch the forecast: trusses can be set in light cold, but wind, ice, and wet sheathing shut the job down. Equipment choices shape the schedule; one steel erection job showed how a single high-capacity crane replaced two smaller units and kept the project on schedule, a lesson that applies when a long roof needs many lifts in a short weather window. A clean sequence ends with a straight ridge, a square roof plane, and a crew that never worked under a load, which makes every trade that follows, from sheathing to shingles, faster and safer.