General Building and Plumbing Code Provisions
Support, protection, and burial
The general regulations chapter is where plumbing meets structure. Pipes must be supported at code intervals - commonly cited maximum horizontal spacing is 4 feet for ABS/PVC, 5 feet for cast iron, 6 feet for copper 1¼ inch and smaller, and 10 feet for larger copper - with vertical piping supported at each story. Water service is buried below the local frost depth, and piping is kept out of exterior walls where practical because Idaho winters are unforgiving.
- Sleeves through concrete and masonry provide clearance so pipe is not rigidly embedded and can move.
- Penetrations of fire-rated assemblies are sealed with an approved firestop system; plastic pipe needs a listed device or sealant.
- Buried ferrous pipe is protected against corrosion; bedding is free of rock and voids.
- Copper-to-steel or copper-to-galvanized connections use dielectric fittings to stop galvanic corrosion.
Coordination with the building code
- Notching and boring of structural members is limited by the building code; engineered lumber is not drilled without approval.
- Concealed valves, cleanouts, and backflow assemblies need access.
- Fixtures belong in rooms that satisfy the building code's light, ventilation, and privacy provisions.
- Drainage and vent piping is tested before concealment.
Worked example
A 20-foot horizontal run of ¾-inch copper in a basement ceiling must be supported. Copper at 1¼ inch and smaller is supported at 6-foot intervals, so supports are needed at roughly 0, 6, 12, and 18 feet, plus support near the termination to keep the run straight. Answer 4 supports, and show the spacing rule - the examiner grades the rule, not the arithmetic.
Traps
- Applying the 10-foot copper spacing to small-diameter tube.
- Omitting a firestop because the wall was "already closed."
- Connecting new copper directly to existing galvanized without a dielectric union.
- Bedding pipe directly on excavated rock.