Join wide square duct with S-and-drive
Wide rectangular duct
Before you start
- Confirm the duct size, end construction, pressure class, seal class, and joint shown on the approved shop drawing.
- Inspect both duct ends for crushed corners, torn locks, bowed panels, loose reinforcement, or shop damage before lifting them into place.
- Make sure the supports are already installed or the sections are otherwise held so the joint is not carrying the weight of the run.
- Stage the correct S-cleats, drive cleats, sealant, hand tools, clamps, and access equipment before starting the joint.
- Verify the wide duct has the reinforcement, tie rods, and support arrangement required by the approved construction details.
Lay it out
- Establish a level bottom plane across the full duct width; a wide duct can look aligned at one corner while the opposite side is several inches out.
- Check that reinforcement angles, tie rods, or standing seams will not block the S-cleat or the planned support location.
- Plan enough lift and platform access for workers to see both side locks without leaning over guardrails.
Set and support it
- Install and level the wide trapezes before the duct is lifted.
- Support both sections close to the joint so the bottom panels do not belly and the weight does not spread the locks.
- Use more than one control point across the width. Confirm both side corners and the center of the bottom panel are at the correct elevation.
Make the connection
- 1
Fit the top and bottom S-cleats while the sections are still controlled and square.
- 2
Bring the wide faces together slowly. Watch for the center of the panel bowing before the corners meet.
- 3
Use stretchers or clamps at the side locks in small steps, checking that the center and opposite side remain aligned.
- 4
Start both drives before fully seating either one.
- 5
Seat the drives gradually, moving from side to side while checking for racking and panel distortion.
- 6
Verify reinforcement remains straight and does not press against the adjoining section.
- 7
Finish the drive ends and seal the joint only after the duct is stable on its permanent supports.
Check the install
- The full-width S-cleats are engaged with no section of hem outside the lock.
- The bottom panel is not bellied, oil-canned, or pulled upward at the joint.
- Both side walls remain plumb and the duct dimensions are maintained.
- Reinforcement and tie rods remain straight and clear of the joint.
- The trapeze carries the load evenly across the duct width.
Common mistakes
- Lining up only the near side because the far side cannot be seen from one lift.
- Using undersized temporary support that allows the center panel to sag.
- Fully driving one side and twisting the opposite side out of alignment.
- Trying to close a joint when one piece has been fabricated out of square.
Stop and ask
Stop if the duct bows under its own weight, reinforcement is missing or damaged, the far side cannot be safely accessed, or the joint requires excessive force to close.