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MIT's flat roofs are the largest contributor to Cambridge's UHI; The best chance to reduce the city's temp is to cover them with vegetation.



According to the map of Ambient Air Temperatures provided in the reference materials, the areas of highest air temperature are (in W to E order):

1) The Commercial space in W Cambridge north of Fresh Pond

2) The MIT campus

3) The Commercial space in E Cambridge north of Binney St

(The Harvard campus doesn't seem to be that warm and may be a source of valuable insight on temperature mitigation)

I am proposing that the first action on the UHI effect is to install vegetated roofs aka "green roofs" on all flat roofs where available and applicable in decreasing order of ROI and ease of installation (permitting, labor, ownership, etc)

The General Services Administration (GSA), the agency in charge of all federal buildings has installed more than 2 million square ft of green roofs and has found that on a 10,000 sqft flat roof, a 3 - 6 in system will have a 6 year pay back, and NPV of $2.70/sqft.

(Exact #s will be different in Cambridge due to climate, building usage, utility and labor costs, etc)

A standard flat black roof temperature may exceed ambient by 50 degrees Celsius. The temperature of a green roof, while not quantified over a large dataset is generally less than the ambient.

The 3 Phases of The Project

1) Rooftop Analysis: During this phase, the various roofs of the 3 high-temperature zones will be analyzed for potential green roof installation. Tangible and intangible costs and benefits will be studied to choose the best roofs for project rollout. 

2) Partnership and Funding: With a negative financial ROI from the cooling, grants, gov subsidies, and savings to the "commons" will need to be used to finance the projects.

3) Installation & Publicity: Installing the green roofs in a decreasing ROI order will increase available funds as time goes on through savings. The large, public-use nature of these buildings will provide free marketing to spread the benefits to the general public.

Category of the action


Who will take these actions?

The key actors will vary depending on the phase of the project.

For phase 1, the analysis will be done by open-source team led by Contest Selection Team. (students, government employees, interested citizens et al). Each building/roof will undergo the same research and analysis for costs & potential benefits on the UHI effect and other concerns and available government assistance.

For phase 2, team leaders will pitch government entitiies and building owners to move forward with the installations including financing options. Municipal, county and state government will be brought in at this point to help with financing, permitting, etc. 

For phase 3, contractors will submit bids for different roofs based on ownership of the building and what is permissible. For MIT buildings employees and/or students may be able to do the work, thus lowering costs and providing a greater education experience for the students on campus.

Also during phase 3 local and national news would be invited to view the projects and further spread awareness of the benefits of green roofs on UHIs.

What are other key benefits?

Besides reducing the UHI effect in Cambridge, these green roofs will offer several additional benefits. 

1) Reduced utility usage inside the buildings: Green roofs have shown to reduce cooling usage by as much as 50% on the floor below the roof. This will save money for the building owner and potentially reduce power plant emissions.

2) Improved air quality around the building: Green roofs, like all living plants, filter the air of toxins for us.

3) Reduced storm water runoff: As the plants take up the water, as much as 65% less water will runoff into the storm drains and rivers. This will lessen the loads on municipal water systems saving money and also reduce the flow of pollutants into the city waterways.

4) Reduce the number of Heat Related Illnesses: Approximately 1,000 people die in the United States each year due to extreme heat events. A statistical analysis found that for every 10 deg F rise in temperature in San Bernadino County, there was a rise in mortality of 11.4%. 

What are the proposal’s costs?

Negative side effect will be decrease in revenues for asphalt roofing companies.

Costs per sqft decreases as roof size increases (decreasing labor costs and bulk purchasing of materials). The GSA quotes national costs ranging being between $11.50 per sqft and $15/sqft for the installation ($12 premium on this cost of asphalt roof). 

Cost estimates for the Cambridge area are closer to $30 - $40/square foot ($15/sq ft for waterproof membrane + $15-$25/sq ft for plant covering). The primary savings for building owners is in cooling. This is not that great in the greater Boston area so will not be enough on its own to sell the project to a building owner.

10,000 sq ft roof = $25/sq ft

20,000 sq ft roof = $20/sq ft

larger roofs should see further discounts

Rough Google Map Estimation for Viable Rooftop Area: 5 - 8M sqft

Rough cost estimate: $200M - $320M.

Variables to Bring Cost Down:

1) Size of Project: Reducing the number of green roofs installed will directly reduce the initial cost of the project.

2) Labor: If MIT can get student labor involved then this cost may drop dramatically. Also, larger roofs and larger projects will have lower $/sqft costs.

3) Bulk Purchase Ordering: Buying materials and labor orders on a large scale will reduce costs. 

4) Tax credits/exemptions & Grants: Depending on ownership, non-profit building owners will be able to purchase materials without taxes. There may be grants or tax credits available to reduce the cost further.

Time line

The technology exists now and so this project could begin immediately. 

Depending on the interest in joining the research team, phase 1 should take between 6 and 12 months. 

Phase 2 will take a further 6 - 12 months depending on the decision making process of the building ownership and financing options. This could be shortened if it begins before phase 1 ends. Bringing building owners and stakeholders (students, faculty, alumni, government agencies) into the process earlier will give them more time to study it themselves and get accustomed to the idea instead of having it "sprung" on them.

Phase 3 should take between 3 and 6 months depending on weather conditions, material availability and the number of roofs chosen.

The next 3 years are the "establishment" phase with higher maintenance costs to ensure the green roof survives and becomes more self-sustainable.

After that, the roofs will last approximately 50 years, 60 - 100% longer than conventional roofing.

Related proposals

Greening Roof with Real Plants: Plant gardens on roofs (very similar to this proposal)

Cool Roof Coatings: Primarily through lighter &reflective colors & coatings

Integrated UHI Strategy: Discusses green roofs and focuses on homes

Turn Flat Roofs into Greenhouses: Build greenhouses on top of 3 story flat-roofed buildings.


I linked directly to these papers in the relevant sections above as well.

Cost of Asphalt Roof


Report for an analysis of a green roof in upstate NY showed a negative NPV, but positive investment vs a conventional roof covering based on savings and maintenance savings.