The cost of a green roof varies based on factors such as roof size, location, accessibility, warranty, depth of the growing medium, and whether it requires additional structural support.
On average, it has been shown that green roof installation costs per square foot decrease as size increases. Typically the decrease is by a factor of at least 3 as size increases from, (i.e 1,000 square foot roof to a 20,000 square foot roof).
- The installed cost premium for multi-course extensive green roofs ranges from $10.30 to $12.50 per square foot more compared to a conventional, black roof.
- The installed cost premium for semi-intensive green roofs ranges from $16.20 to $19.70 per square foot more compared to a conventional, black roof.
- This cost includes purchasing plants such as sedums that can cost $25-35 for 40-50 plants.
- Annual maintenance for a green roof is typically higher than for a black roof, by $0.21 to $0.31 per square foot.
- This maintenance includes the establishment period where there will be an average of two workers doing a total of about 4 hours per 1000 square feet per year. (The calculation of the cost to hire two workers per year will depend on the salary of the gardener in that area).
- Additional costs include time, location, and accessibility:
- Whether or not, a green roof was done in the past, costs may have fluctuated since then
- Whether or not, a green roof is built on a skyscraper or high rise building versus a lower level building
- Whether or not, the building has easy accessibility or would workers need special gear to gain access
Return on Investment
Besides the environmental and aesthetic benefits of a green roof, many commercial companies want to know the answer to one crucial question; “what’s the return on the investment after I install the green roof?”. Actually this can be a difficult or relatively simple answer. Want to know the answer?
ANSWER: It depends!
Let’s establish what a return on investment (ROI) means. A return on investment is the percentage of money gained or lost on an investment, relative to the initial cost.
Simple Answer Based on Case Studies
Based on a cost-benefit analysis done by the GSA:
- On average it is observed nationally that most green roofs get an ROI of 220%, 224%, 247% on a 5,000, 10,000, 50,000 sq.ft roof respectively.
- Green roofs save about $19 per square foot in energy savings and stormwater benefits.
- A net present value at a savings of almost $38 per square foot of roof is observed for the community.
- All of these benefits can occur on average in 6.2 years
Harder Answer that Depends
Most of the time it depends on certain factors that the installer will have to make the decision on what is prioritized as a return on investment. These include:
- Customer/Visitor appreciation for the aesthetic of the design of the green roof which could attract more sales and increase the ROI
- Ranking on LEED-certified buildings can increase the value of the property and allow for more profitability
- Government incentives can give rebates or tax credit which can reduce the overall cost of the roof or future costs in other aspects (i.e tax).
As you can see, the ROI in these situations are all variable and will depend on unpredictable factors that will contribute to a developer’s decision to install a green roof.