Living Roof Calculator

Calculate green roof structural loading, stormwater retention capacity, thermal performance, and cost for extensive or intensive systems.

Roof Area (sq ft)

Growing Media Depth (in)

Saturated Media Density (lb/ft³)

Drainage Layer Weight (psf)

Annual Rainfall (in)

Roof Slope (degrees)

Existing Roof Dead Load (psf)

Tab to move between fields

Green Roof System Weight (psf)

34.3

Total Dead Load (psf)49.3

Storm Retention (gal)2,449

Annual Retention (%)60.9%

Annual Retained (gal)27,325

Added R-Value2.8

Energy Savings ($/yr)$250.00

Roof TypeExtensive (sedums, low maintenance)

Estimated Cost$30,000.00

How to Use This Calculator

Enter Roof Area in sq ft and Growing Media Depth in inches (2–6 in extensive, 12+ in intensive).
Enter Saturated Media Density in lb/ft³ and Drainage Layer Weight in psf.
Enter Annual Rainfall in inches, Roof Slope in degrees, and existing Roof Dead Load in psf.
Review Green Roof System Weight and Total Dead Load — verify structural capacity is not exceeded.
Check Annual Stormwater Retention, R-Value Addition, and Annual Energy Savings.

How the result changes with Growing Media Depth (in)

Roof Area (sq ft): Area of roof to be covered with the green roof system.
Growing Media Depth (in): Depth of growing media. Extensive: 2-6 in, semi-intensive: 6-12 in, intensive: 12-48 in.
Saturated Media Density (lb/ft³): Density of growing media at full saturation. Engineered green roof media: 70-100 lb/ft³.
Drainage Layer Weight (psf): Weight of the drainage/retention layer per square foot.
Annual Rainfall (in): Average annual precipitation for your location. US range: 5-65 inches.
Roof Slope (degrees): Slope of the roof surface. Most green roofs require < 30°. Steeper slopes need retention grids.
Existing Roof Dead Load (psf): Weight of the existing roof assembly (membrane, insulation, deck) before adding the green roof.

Green Roof System Weight (psf): Total weight of the green roof system at full saturation (worst case for structural design).
Total Dead Load (psf): Combined existing roof + green roof system weight. Must not exceed structural capacity.
Storm Retention (gal): Maximum water retention capacity of the system per storm event.
Annual Retention (%): Estimated percentage of annual rainfall retained by the green roof.
Annual Retained (gal): Estimated total gallons of stormwater retained per year.
Added R-Value: Approximate thermal resistance added by the growing media.
Energy Savings ($/yr): Estimated annual energy cost savings from reduced heat flux through the roof.

Identify Input Parameters
4 parameters
Roof Area (sq ft) = 2000, Growing Media Depth (in) = 4, Saturated Media Density (lb/ft³) = 85, Drainage Layer Weight (psf) = 3 = 7 input(s) provided
Calculate Green Roof System Weight
Green Roof System Weight = mediaWeight + drainageLayerWeight + vegetationWeight + filterWeight
34.3 = 34.3
Calculate Total Dead Load
Total Dead Load = existingDeadLoad + systemWeight
49.3 = 49.3
Calculate Storm Retention
Storm Retention = retentionDepth * roofArea * 0.623
2449 = 2449