Downspout discharge — IRC R401.3 surface drainage + City of Houston Chapter 9 stormwater

International Residential Code Section R401.3 establishes the surface drainage framework that downspout placement supports. The code requires that surface drainage be diverted to a storm sewer or other approved point of collection that does not create a hazard, that lots be graded to drain surface water away from foundation walls with a minimum 6-inch fall in the first 10 feet, and that impervious surfaces (driveways, patios, walkways) within 10 feet of the building be sloped at a minimum of 2 percent away from the structure. A common homeowner misconception is that the IRC specifies a minimum downspout discharge distance from the foundation — it does not. The code requires drainage away from the structure but leaves the specific downspout-to-foundation distance to local jurisdiction and engineering practice; common contractor-quoted distances of 4-6 feet are practitioner conventions, not code minimums. Three common downspout discharge approaches: splash blocks at the downspout boot directing flow onto graded soil (the lowest-cost approach, dependent on the lot grading meeting R401.3); flexible downspout extensions carrying water further from the foundation before discharge (useful when the lot grade is marginal); and subsurface drains (PVC pipe buried below grade) carrying water to a daylight outlet, drywell, or municipal connection. In the City of Houston specifically, the Infrastructure Design Manual Chapter 9 governs stormwater discharge. For residential stormwater outfall to a curb cut, the City specifies a 6-inch restrictor reduced to a 4-inch Schedule 40 PVC pipe; subsurface drainage systems are required to be drained within 48 hours. Improper downspout placement — discharging at the foundation rather than away from it — is one of the most common contributors to slab and pier-and-beam foundation issues in Houston-area homes. [Source: 2021 International Residential Code Chapter 4 Section R401.3; 2024 International Residential Code Chapter 4 Section R401.3; City of Houston Infrastructure Design Manual Chapter 9 stormwater design and water quality]