Aspiring rooftop gardeners and farmers often ask me what to look for when selecting a building on which to build their skyline gem. This is an important question, as you never want to commit yourself to a rooftop that will cost you in upgrades. Rooftop gardeners, here are the key features to look for on an existing roof:
1| Structural integrity – If you’re interested in a garden larger than a few potted plants, hire a licensed structural engineer to evaluate the strength of your roof. Your roof may not be as strong as you think, and so you’d be wise to have the structure investigated by a professional.
2| Building codes – Check your local building codes to find out how you are permitted to access your roof on a regular basis. Is a staircase up to the roof (i.e. with a “headhouse”) required? Do you or your neighbor have an existing headhouse that can be used for garden access? What does the building code require for fall protection and setbacks? Do you need to install a railing system?
3| Waterproofing condition – How does your roof’s waterproofing membrane look? Was the membrane installed within the past 5 years? Have you experienced any leaks? If it’s time to re-roof than complete this task before hauling plants up the roof. If the membrane looks good, consider placing walk pads or even building a deck in order to avoid ware and tear from foot traffic. Jay Sand, owner of a townhouse in Philadelphia, opted to install a roof deck and railing to distribute the planter loads across his roof, protect his waterproofing membrane, and keep his kids safe (see image).
4| Water hookup – Your rooftop plants will get thirsty! How will you water them? Is there an existing hose bib on the roof? Can you stretch a hose from your kitchen or bathroom to the roof without springing a leak? Be sure to think this step through, and consider hiring a plumber to install a water line and hose bib if necessary.
Considerations for rooftop farmers may sound similar to those for gardeners, but the details are quite different. Here are the primary considerations when selecting a roof for your commercial venture:
1| Zoning – Does the local zoning code permit commercial food production in the area in which your building is located? If not, are you able to apply for a zoning variance?
2| Structural integrity – Before you get too attached to the building you’ve been pining for, hire a licensed structural engineer to evaluate the load capacity of your building. He or she should provide you with dead load allowances across each roof area, which will be in addition to the snow load, wind load, and live load requirements. Many local building codes require a live load of 100 pounds per square foot for regularly accessed roofs. The remaining dead load allowance must be sufficient to allow for the soil depth you have in mind for your crops. Make sure you and the engineer crunch the numbers before committing to the building.
3| Access – How will you, your employees, interns, volunteers, and visitors access the roof? Is there an existing staircase, or better yet a freight elevator that extends all the way to the roof? Carrying compost and loads of vegetables up and down the stairs can be exhausting and inefficient. Time is money up on a roof, and efficient access and transportation must be prioritized. Increasing the height of an existing elevator within the building may cost upwards of $100,000, a hefty line item that most people do not include in their budget!
4| Fall protection – Does the building of your dreams contain a high parapet or railing system all the way around the roof’s perimeter? The local building code will dictate the required height of this safety feature, which is intended to keep rooftop visitors from tumbling over the edge! Keep in mind that the specified height is measured from the walking surface to the top of the railing. If you install 12″ of growth media, your parapet or railing must factor this added foot.
5| Waterproofing condition – What is the physical condition of the roof’s existing waterproofing membrane? Replacing a membrane can be one of the most expensive parts of building a rooftop farm, and so it’s best to find a building with a new membrane whenever possible. Is the existing membrane under warranty by the waterproofing provider? How will installing a rooftop farm on top of the membrane affect this warranty?
6| Microclimate – What are the wind and temperature conditions like on the roof? Have you visited the roof several times, perhaps even during different seasons? The taller the building the more extreme the growing conditions may be, so keep this in mind when selecting your roof.
7| Proximity to sales outlets – The final consideration is the buildings proximity to prospective sales outlets. Are there markets or restaurants nearby with which you’re already under contract? Have you started marketing a rooftop CSA? This consideration is integral to the success of your farm, and must be thought through when developing your business and marketing plans.