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Green Roof & Rooftop Garden Calculators

Professional structural load tools for extensive and intensive green roofs. Calculate saturated dead loads, stratigraphy build-up, drainage capacity, runoff reduction, and thermal performance for rooftop landscape design.

System Type
Layer Build-up
Auto-filled from preset. Edit or add layers as required (top to bottom).
Stratigraphy Profile
Total Build-up Depth
–
mm
Dry Dead Load
–
kN/m²
Saturated Dead Load
–
kN/m²
Extra Load When Saturated
–
kN/m²
Total Dry Weight on Structure
–
kN
Total Saturated Weight
–
kN
Substrate Volume
–
m³
Substrate Weight (Sat)
–
tonnes
GRO Code 2021 / FLL 2018: dry dead load = sum(depth_m × dry_density × 9.81/1000) kN/m². Saturated load uses saturated density. Ensure structural engineer confirms capacity before specifying system type.
Existing Structure
Applied Green Roof Loads
Auto from Tab 1 or manual
Factored Design Load ULS
–
kN/m²
Unfactored Applied Load
–
kN/m²
Maintenance LL Applied
–
kN/m²
Allowable Capacity
–
kN/m²
Reserve Capacity
–
kN/m²
Structural Utilisation
–
%
Total Load on Structure
–
kN
Utilisation Status
BS EN 1991-1-1 Eurocode 1: ULS = 1.35×DL + 1.5×LL. Allowable capacity = SDL allowance + LL allowance. Utilisation = factored load / allowable × 100. Design to ≤80% utilisation to maintain serviceability reserve. Always verify with structural engineer.
Hydrology Parameters
Design Peak Runoff — Green Roof
–
l/s
Design Peak Runoff — Greenfield
–
l/s
Runoff Reduction vs Conventional
–
%
Annual Rainfall Retained
–
m³/yr
Storm Event Retention
–
mm
Time to Overflow
–
min
Annual SuDS Credit
–
m³/yr
Outlet Capacity Adequate
GRO Code / CIRIA C753: Extensive roofs retain 50–80% annual rainfall. Runoff coefficient: extensive Cv=0.3–0.5, intensive Cv=0.1–0.3 vs conventional roof Cv=0.9. Storage = drainage layer + substrate retention capacity.
Roof Geometry
Waterproofing System
Roof Drainage Plan
Max Ponding Depth
–
mm
Roof Area
–
m²
Falls Achieved
–
%
Outlet Catchment per Drain
–
m²
Flow per Outlet at Design Storm
–
l/s
Liner / Membrane Area
–
m² (incl. upstands)
Falls Compliant
Outlet Size Adequate
Upstand Height Adequate
BS 6229:2003: minimum falls 1:80 on flat roofs to prevent ponding. Drainage outlet sizing: Q = C×A×i where C=0.9, A=catchment area, i=design intensity. Upstand height: min 150mm above finished substrate level (GRO Code).
Build-up Thermal Properties
Auto from Tab 1 or manual
UK Part L: 0.15 flat roofs
U-value Achieved
–
W/m²K
Total R-value
–
m²K/W
Additional Insulation Needed
–
mm (if failing)
Annual Heat Loss Reduction
–
kWh/m²/yr
Annual CO₂ Saving
–
kg CO₂/m²/yr
Annual Energy Cost Saving
–
$/m²/yr
U-value Target Met
BS EN ISO 6946: U-value = 1 / (Rsi + R_layers + Rse). Surface resistances: Rsi=0.10, Rse=0.04 m²K/W. Substrate thermal conductivity varies with moisture content; use saturated value (0.08–0.15 W/mK typically). UK Part L 2022: flat roof U-value ≤0.15 W/m²K.
Planting Category
Planting Load at Maturity
–
kN/m²
Planting Load at Installation
–
kN/m²
Wind Overturning Force per Plant
–
kN
Combined Planting + Wind ULS
–
kN/m²
Recommended Anchorage
–
Structural Reserve Check
GRO Code / Eurocode 1: Tree wind load = Cf × qp × reference_area (crown). Use load combination: 1.35×DL(mature) + 1.5×Wind. Check against structural reserve from Tab 2. Single large trees may require individual structural assessment.

CalcType: Professional Green Roof & Rooftop Garden Structural Solutions — This comprehensive green roof and rooftop garden calculator is engineered to support evidence-based structural load assessment, drainage design, and thermal performance modelling for landscape architects, building engineers, and rooftop garden specialists. Utilising load conventions aligned with EN 1991-1-1 (Eurocode 1), ASCE 7-22, and AS/NZS 1170.1, the platform calculates precise dry and saturated dead loads for all green roof stratigraphy layers — including growing media, drainage panels, filter fleece, root barriers, and waterproofing membranes — enabling accurate superimposed load assessments for existing and new structures. The Structural Check module verifies utilisation ratios against allowable superimposed dead load capacities, while the Drainage & Runoff module quantifies peak inflow, substrate water storage, and annual runoff reduction in accordance with CIRIA C753 and FLL Green Roof Guidelines. Thermal performance calculations follow EN ISO 6946 and ASHRAE 90.1 principles for vegetated assemblies. Whether you are designing a lightweight extensive sedum roof, an intensive rooftop terrace with specimen trees, or a podium garden over a structural car park, CalcType provides the technical rigour required for safe, compliant, and climatically responsive rooftop landscape design. Technical Disclaimer: The structural loads, drainage figures, and thermal data provided by this calculator are intended for preliminary estimation and schematic design purposes only; all final structural assessments, waterproofing specifications, drainage designs, and energy compliance reports must be verified by a licensed structural engineer (PE / CEng / MIStructE), qualified waterproofing specialist, and certified landscape architect (PLA) prior to construction or building permit submission. Actual saturated substrate densities, membrane root-resistance ratings, and deflection profiles will vary by manufacturer and site-specific conditions; therefore, CalcType assumes no liability for structural failure, membrane breach, water ingress, or financial losses resulting from the use of these estimation tools.