What is the maximum drainage fixture units for a horizontal branch using a 4-inch pipe?

What is the maximum drainage fixture units for a horizontal branch using a 4-inch pipe?

• A. 1 DFU
• B. 20 DFU
• C. 100 DFU
• D. 3 DFU

Answer: (C)

In drainage design, drainage fixture units (DFUs) measure the load a branch line must carry from connected fixtures. The total DFU on a horizontal branch is limited by the pipe’s size, with code tables specifying the maximum allowed DFUs for each diameter. For a four-inch horizontal branch, the maximum is 100 DFU, meaning the sum of all fixtures on that branch should not exceed 100. If you exceed that, you’d need to split the load into another branch or upsize the pipe to maintain proper drainage. The other numbers are far too small to represent the capacity of a 4-inch branch and would apply to much smaller pipe sizes.

In drainage design, drainage fixture units (DFUs) measure the load a branch line must carry from connected fixtures. The total DFU on a horizontal branch is limited by the pipe’s size, with code tables specifying the maximum allowed DFUs for each diameter. For a four-inch horizontal branch, the maximum is 100 DFU, meaning the sum of all fixtures on that branch should not exceed 100. If you exceed that, you’d need to split the load into another branch or upsize the pipe to maintain proper drainage. The other numbers are far too small to represent the capacity of a 4-inch branch and would apply to much smaller pipe sizes.