UPDATE: We've summarized much of the series this article is part of in a new report, Policies for Shareable Cities: A Sharing Economy Policy Primer for Urban Leaders. Get your free copy here today.

The sky’s the limit when it comes to getting creative with our rooftops. As we run out of horizontal spaces in our cities, rooftops come to mind as an important resource. Because they get more sun than almost anywhere else, we should harness rooftop spaces to collect solar energy, grow plants, or create sunny social spaces. Rooftops also make first contact with a large amount of rainwater, which makes them prime candidates for the collection and management of water. The way we use our rooftops can also greatly affect a building’s energy efficiency and the overall environmental quality of a city.

A rooftop garden in Southern California. Photo credit: La Citta Vita. Used under Creative Commons license.

At the same time, many ways that we might use our rooftops are costly and may present legal barriers. Here are a few suggestions for ways that cities can adopt policies to encourage communities to make smart use of rooftops:

1. Exempt height and square-footage limitations for certain rooftop uses: Nearly all zoning codes impose height limitations on buildings. Yet, rooftops are a prime location for greenhouses. Cities should loosen height limitations and create a streamlined permit process for people wishing to put a greenhouse structure on their roofs. Also, where a new building project would otherwise have a limitation on the square footage of floor area, a rooftop garden space or roof deck should not be taken into account. To encourage green roofs, the City of Cambridge, Massachusetts, passed an ordinance removing roof gardens from the calculation of total square footage of a new project.

2. Create streamlined building inspection and approval processes for rooftop gardens: The permitting requirements for roof gardens are often somewhat unclear, so it would help if a city could appoint a rooftop garden specialist to give guidance to gardeners. The funny thing is that you may not need a permit to put a few potted plants on your roof, but if you are planning to put a LOT of plants on your roof, the city building department might perk up at some point and decide you need a permit. One rooftop garden project in Queens, New York, ground to a halt when the city, understandably, noticed and realized that putting a million pounds of dirt on the roof might cause problems. Cities are right to want to protect residents from collapsing roofs and, thus, should make it easy for residents to get information, advice, and permits for their projects. The City of Chicago has taken some helpful steps by publishing a guide to rooftop gardens.

3. Offer subsidies for roof reinforcements and green roof construction: The City of Portland has recognized the value of green roofs in reducing energy use, cleaning the air, and managing storm water run-off. Portland’s Ecoroof Incentive Program offers to pay for $5 per square foot of green roof space created. Some roof gardens might require that a building and roof be retrofitted and reinforced to accommodate the weight. Such costly retrofits could be offset by a city subsidy or loan program. Many cities in Europe have made great strides toward encouraging or even requiring green roofs on new buildings, as described in this helpful resource documenting green roof policies.

4. Disincentivize deadbeat rooftops: It makes sense for cities to not only incentivize wise use of rooftops, but to also disincentivize rooftops that aren’t being put to good use. In Philadelphia, Pennsylvania, to prevent stormwater floods and to incentivize capture, storage, and percolation of rainwater, the city imposes a tax on properties based on the size of impervious space on the property. If a property has a large roof that simply drains into the sewer system, the tax on that property could be quite high. If the roof instead contains a garden to capture and use the rain water, the tax on the property would be much lower. Capturing and storing water in a cistern for later use would also lower the tax.

Please help us add to this collection of policy suggestions by adding comments and ideas below. Thank you!

This post is one of 15 parts of our Policies for a Shareable City series with the Sustainable Economies Law Center:

1. Car Sharing and Parking Sharing
2. Ride Sharing
3. Bike Sharing
4. Shareable Commercial Spaces
5. Shareable Housing
6. Homes as Sharing Hubs
7. Shareable Neighborhoods
8. Shareable Workspaces
9. Recreational and Green Spaces
10. Shareable Rooftops
11. Urban Agriculture
12. Food Sharing
13. Public Libraries
14. The Shareable City Employee
15. How to Rebuild the City as a Platform