Rain garden / bioretention: shallow depression with engineered soil + plantings; sized to ~10% of impervious area drained

Description

A rain garden (a.k.a. bioretention) is a shallow planted depression that captures + infiltrates stormwater runoff from roofs + driveways. Typical sizing: surface area approximately 10% of the impervious area drained, with a ponding depth of 6-12 in and an engineered soil mix 18-36 in deep. Underdrains (perforated pipe in gravel) discharge slow infiltration to the storm system. Planted with deep-rooted native + adapted species that tolerate alternating wet + dry.

Why this exists

Rain gardens dramatically reduce runoff peak + volume + pollutant loads. They're aesthetic site amenities, not engineering eyesores — and they're often the cheapest path to stormwater-permit compliance for residential developments. Architects designing larger residential lots should consider rain gardens at downspout discharge points as a default.

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Categories

Source

Solver enforcement

Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.

Related directives

• Exterior ramps: maximum slope 1:12, minimum 36 inch clear width · HUD FHA Design Manual Chapter Two §2.7
• Build to the latest natural-hazard-resistant code edition · FEMA P-2325 §Building Codes Basics
• Coastal-pile foundations should embed deeply to resist erosion + uplift · FEMA P-2325 §Florida Building Code / Sand Palace lessons
• Lowest floor at or above Base Flood Elevation in Special Flood Hazard Areas · FEMA P-2325 §Flood Hazard Provisions
• In WUI zones, protect openings from wind-blown embers · FEMA P-2325 §Wildland-Urban Interface (WUI)