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The total plan area covered by modular green roof trays.
Measure the total area of the roof covered by the modular vegetated tray system, not the whole roof if only part of it is a green roof.
The manufacturer's rated water retention depth for the tray/media system.
This is the equivalent depth of water the tray system can hold at saturation before it runs off, as rated by the tray or growing-media manufacturer.
Retained rainwater volume
337 gal
Retention depth is the manufacturer's rated figure for the specific tray/media system at saturation — actual retention varies with antecedent moisture and rainfall intensity/duration.
They open the calculator with your figures already in it
Green Roof Vegetated Tray Rainwater Retention Calculator: 337 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Retained volume = tray area × the tray system's rated water retention depth, the standard method for estimating a modular green roof system's stormwater retention capacity
Inputs used
- Total Vegetated Tray Area
- 540 sq ft
- Rated Water Retention Depth
- 1 in
Confidence note: Retention depth is the manufacturer's rated figure for the specific tray/media system at saturation — actual retention varies with antecedent moisture and rainfall intensity/duration.
What this calculation does not cover
- This is the ceiling for one storm landing on dry media, not a capacity that resets on demand. The only thing that empties a green roof between storms is evapotranspiration, which runs a few mm (around 0.1 in) on a good summer day and close to nothing in winter, so a second storm twelve hours behind the first meets a full tray and passes straight through. Stormwater credit is assessed against a continuous rainfall record with that drawdown rate built in, and it comes out well below the figure above.
- The rated depth is a level-tray figure, and slope drains it. Water occupies the tray's reservoir profile only while that profile is level; as pitch increases it migrates to the low side of each module and out, so the depth published for a flat test bed is not what a pitched roof holds. Above the shallow falls these systems are rated at, treat retention as reduced and ask the supplier for a figure at the actual pitch.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Retained volume = tray area × the tray system's rated water retention depth, the standard method for estimating a modular green roof system's stormwater retention capacity
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