A clothes-washer standpipe connects to a 2-inch horizontal sanitary drainage pipe. Under 2024 IRC P3005.3 (May 2024 printing), what is the minimum uniform slope of this horizontal pipe?
- 1/4 inch per foot
- B1/8 inch per foot
- C1/2 inch per foot
- D3/8 inch per foot
Where to look it up
https://codes.iccsafe.org/content/IRC2024P2/chapter-30-sanitary-drainage
Why A is correct
The stated 2-inch horizontal pipe falls in P3005.3’s 2-1/2-inch-and-smaller category, requiring at least 1/4 inch per foot. A washer connection does not create a general 1/2-inch-per-foot minimum. This question concerns the horizontal gravity drain, not the appliance’s pumped discharge hose. The old P276.1 reference was not the applicable drainage rule. Source: https://codes.iccsafe.org/content/IRC2024P2/chapter-30-sanitary-drainage