Sink Drain P-Traps vs. Toilet Rough-In & Flange
Comparing 2 standards across 12 specifications. 12 key differences identified.
Sink drain P-traps are curved sanitary fittings governed by ASME A112.18.2 that maintain a 2-to-4 inch liquid seal barrier to block municipal sewer gases from entering living spaces. Sized in 1-1/4" tubular for bathroom lavatories and 1-1/2" for kitchen sinks, P-traps join via slip-joint compression washers and threaded slip nuts.
Toilet rough-in dimensions under ASME A112.19.2 define the exact centerline distance from the finished rear wall to the closet bolts on the floor flange. While 12.0 inches (305 mm) is the universal modern standard, 10-inch and 14-inch rough-in toilets accommodate legacy plumbing and thick tile remodels, sealing to a 4"×3" closet flange via a wax ring or rubber gasket.
Specification Comparison Table
12 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
ASME A112.18.2 / CSA B125.2 / IPC / UPC | ASME A112.19.2 / CSA B45.1 / ANSI A112.19.5 |
|
Trap Seal Depth
|
2 to 4 inches (51 to 102 mm) of standing water column | — |
|
Bathroom Lavatory Sizing
|
1-1/4" Tubular (31.75 mm OD) brass or polypropylene | — |
|
Kitchen & Utility Sizing
|
1-1/2" Tubular (38.1 mm OD) brass or Schedule 40 PVC/ABS | — |
|
Connecting Mechanism
|
Beveled poly/rubber slip washer + threaded slip nut | — |
|
Maximum Trap Arm Distance
|
1-1/4": 5 ft (1.5 m) | 1-1/2": 6 ft (1.8 m) to vent stack | — |
|
Standard Rough-In Distance
|
— | 12.0 inches (305 mm) from finished wall to center of flange |
|
Alternative Rough-Ins
|
— | 10.0 inches (254 mm) compact | 14.0 inches (356 mm) legacy |
|
Closet Flange Size
|
— | 4" × 3" (fits inside 4" DWV pipe or over 3" DWV pipe) |
|
Closet Bolt Spacing & Size
|
— | 6.0 inches (152 mm) apart | 5/16"-18 or 1/4"-20 brass bolts |
|
Finished Floor Flange Height
|
— | Flange bottom must rest flush on top of finished flooring (1/4" proud) |
|
Sanitary Water Closet Seal
|
— | 100% pure petroleum wax gasket with poly horn or silicone elastomer |