Hangers, Restraint, and Seismic Protection
This domain tests support spacing, restraint of forces, and the seismic provisions that keep pipe in place during an earthquake.
Hanger spacing
- Maximum spacing is 12 ft for pipe 1 inch and smaller, and 15 ft for 1 1/4 inch and larger.
- Hangers must be listed, attached to the building structure, and must not be supported from other trades' piping, ductwork, or ceiling grid.
- Provide support near the end of a branch line and at changes of direction so the pipe is not cantilevered.
- CPVC and some plastic pipe require closer support than steel, per the listing.
Restraint
Underground mains rely on thrust blocks or restrained joints. Aboveground, restraint means sway bracing, riser bracing, and pipe stands where a system needs them. Risers need bracing in both directions, and the bracing must connect to structural members capable of resisting the load.
Seismic protection
Lateral bracing intervals and longitudinal bracing intervals follow NFPA 13 seismic provisions, with bracing placed near the ends of runs and at changes in direction. Flexible couplings are required where pipe crosses a building expansion or seismic separation joint, and clearance is maintained where pipe passes through walls and floors so the building can move without shearing the pipe.
Worked example
A 3 in cross main is hung on 18 ft centers. That exceeds the 15 ft maximum, so intermediate hangers are required at 15 ft or less. The fix is not a longer rod or a stronger insert; the spacing itself is the violation.
Traps
- Quoting 12 ft for all pipe sizes instead of the 1 inch break point.
- Forgetting that a seismic joint requires a flexible coupling and independent support, not a rigid connection.
- Hanging pipe from the ceiling grid in a suspended ceiling.
- Ignoring bracing at the ends of mains and branch lines.