Green Roof¶
Green roofs are governed by BMP Manual Chapter 9.4 in the live source corpus. This page now stays with the source-backed fundamentals: rooftop storage and evapotranspiration, GI status in the live source set, and the roof-system constraints that matter more than soil or SHWT shortcuts.
Structured citation evidence for this page lives in the sibling claim manifest.
Overview¶
In the enrolled source set, a green roof is a rooftop BMP that retains and releases stormwater through growing media, vegetation, and evapotranspiration. That makes it different from infiltration BMPs that depend on native subsoil conditions below grade.
Source Mapping¶
The live citations layer resolves this route directly to the following canonical source bundles.
- Route type:
canonical - 2023 source bundle: Chapter 9.4 (
2023_BMP_9_4) - Green Roofs - 2026 source bundle: Chapter 9.4 (
2026_BMP_9_4) - Green Roofs
Key verified claims already tied to this page manifest: - Green roofs are rooftop storage and ET BMPs in the live source set. - The extensive green-roof category remains the 6-inch-or-less media-depth system. - Green roofs stay tied to the GI and Chapter 14 retention framework in the live source set. - Green-roof maintenance stays tied to vegetation and roof-drain function.
Design Criteria¶
The reconciled design criteria below come from the live crosswalk and page-level claim set, not from the older narrative snapshot.
| Parameter | 2023 source value | 2026 source value | Change |
|---|---|---|---|
| Growing media depth (extensive) | <= 6 in (defines extensive system) | <= 6 in | unknown |
| Volumetric reduction credit (Ch. 14) | ET credit via evapotranspiration volume reduction (no Ch. 14 in 2023 era) | ET credit method via Ch. 14; cistern/reuse required to qualify for full volumetric reduction | modified |
Source-backed criteria that still control this route: - Green roofs are rooftop storage and ET BMPs in the live source set. - The extensive green-roof category remains the 6-inch-or-less media-depth system. - Green roofs stay tied to the GI and Chapter 14 retention framework in the live source set. - Green-roof maintenance stays tied to vegetation and roof-drain function.
Siting Constraints¶
The current source-backed siting review should focus on:
- whether the building and roof assembly can support the selected green-roof system
- whether the drainage and overflow path is compatible with the chapter design
- whether the design is using the BMP for retention and ET rather than pretending it works like a below-grade infiltration BMP
Maintenance¶
The maintenance side is still roof-system specific:
- keep vegetation cover and drainage features functioning
- watch for drainage blockage, media displacement, or loss of vegetative cover
- treat overflow and roof-drain performance as part of BMP performance
Related Pages¶
Source Bundles¶
Use these source bundles when checking the live extracted text or paired OCR evidence:
- 2023 bundle: Chapter 9.4 (
2023_BMP_9_4) - Green Roofs - 2026 bundle: Chapter 9.4 (
2026_BMP_9_4) - Green Roofs