Most commercial rooftops are resigned to house HVAC equipment, lined up in neat rows high above the street. As important as these units are to the building they are taking up some of the building’s most valuable and versatile space. Now developers and owners are starting to see new possibilities. Depending on what you do with a roof, it can serve as a building amenity, efficiency enhancement, storm mitigation, or source of locally grown food. Across urban environments, rooftops are finally getting the thought they deserve from designers, architects, and engineers.
It’s no surprise how we got here. Air conditioning has become a critical part of buildings, providing it requires bulky equipment that needs the space to exhaust hot air. Denied street space in dense cities, the simplest solution is to put the units on the roof, where they reduce clutter, noise pollution, and can be better protected. For most buildings, that means turning the roof into another basement, only accessible to maintenance workers and building staff. But rooftops aren’t basements. Access to sunlight, weather, and some of the best views in the city mean rooftops can be something more when given careful consideration.
The first step in understanding a roof’s possibility is structural analysis. Unlike basements, mostly backed by a foundation or solid ground beneath, rooftops have a maximum load capacity that if exceeded can result in collapse. How much a rooftop can hold is the basis of its potential. Next is to know the current condition or future state of the rooftop membrane, the water-tight covering or coating that keeps the building sealed from the elements. Those two elements are the most important factors in rooftop design.
Nearly as important is rooftop access. Many existing buildings only have some form of maintenance access, making converting the roof into a higher use difficult. Local laws also have a major impact on a roof’s potential. With the variety of rooftop enhancement options available, there’s likely at least one improvement that can be made for every building as long as you understand structural and legal limits.
Higher loads can support a wider array of rooftop uses. A green roof or rooftop garden can be surprisingly heavy, laden with soil and vegetation. Rooftops with lighter loads can still utilize things like lightweight solar panels or bee boxes for pollination. Amenities spaces like rooftop lounges, bars, and pools require public access, complicating rooftop design by necessitating guard rails and other safety measures. It’s also important to consider any work being done on the rooftop is going to come at a steep price. But with this price comes massive potential upside. A good rooftop pool can make headlines, drawing eyes to new developments. Studies have shown patrons tend to stay longer at rooftops venues. Green rooftops have been shown to reduce stormwater runoff and lower the urban heat island effect. Solar panels can augment energy costs, paying for themselves in less than five years. The right design can turn a rooftop into a building’s most defining feature.
“Over the past couple of years, owners and developers are incorporating rooftops as usable space in urban environments,” Furbish Director of Estimating Andrew Benenati said. Furbish designs and installs rooftops that give owners the benefit of green space and energy efficiency at the same time. “They want more roof spaces, amenities, trees, decks, a green roof that has four feet of soil to allow for plants to mature on the roof, Bocce courts. There’s a lot of potential to create amenity space, while still having environmental benefits. Buildings can achieve both things.”
Massive incentives from governments around the globe have green roofs becoming the most popular rooftop augmentation. In Toronto, the Green Roof Bylaw and Eco-Roof Incentive Program adopted in 2009 required any building with a roof larger than 2,000 square meters to have between 20 and 60 percent of the area covered by green roof, depending on the size. The Bylaw set up a system for developers to seek approval to pay $200 a square meter as cash-in-lieu of construction, with that money going towards funding the incentive program, which offered owners $100 a square meter for green roof enhancements and $2-5 a square meter for cool roof projects. In the decade since the law, more than 5.4 million square feet of green roofs have been added to Toronto. Now every year Toronto is saving 22 million liters of stormwater runoff, sequestering 225 tons of carbon, generating 3.2 million kWh from solar power, and saving 1.6 million kWh by reducing the urban heat island effect. Clearly green rooftops have massive potential.
Some type of green roof is possible for most buildings in the right climate. Buildings with lighter load capacities can use “extensive” green roof designs, a low-cost type of green roof that uses a few varieties of plants needing just a thin layer of dirt to create a green barrier between the roof and outside. Think of it like carpeting a rooftop in the grass, arranged neatly between the existing mechanical units. Extensive style green rooftops are best for retrofits and large rooftops, benefiting from a low initial cost and a little upkeep.
“Intensive” rooftops are where the potential for green rooftops gets exciting. The greater structural capacity allows for more dirt, which can support a wider array of vegetation, even trees. A higher capacity means being able to support more visitors on the rooftop, unlocking the potential to turn the space into a true tenant amenity. Intensive rooftops are like a park atop the building. Intensive rooftops are typically what most people imagine when they think of a green roof; lush gardens, walking paths, and a lounge area to enjoy the view. That drives the initial and upkeep costs of intensive rooftops much higher.
“Green roofs change over time, they morph,” Benenati said. “They’re a living system. Plants come and go, plants need to be replaced. We want to set and manage expectations, being forthright on the idea that things will change, that’s not a bad thing, it’s how nature works.”
Both extensive and intensive rooftops can accrue several benefits for your building, according to the EPA. Green roofs help to build shed heat, lowering air-conditioning demand, which in turn decreases associated air pollution and greenhouse gases from energy sources. Evapotranspiration, the process of plants absorbing water and emitting it through leaves also removes heat from the air, acting as additional insulation. Greenroofs also reduce stormwater runoff, retaining storm-related participation during rainy summer months, making them ideal for cities with outdated plumbing and sewer systems. An accessible green roof offers aesthetic value, improving tenant quality of life by adding usable green space to enjoy. The right type of green roof can even support a rooftop bar, restaurant or another type of entertainment o provide additional income.
Climate is the biggest obstacle to green roof implementation. In areas where high winds are common, green rooftops are much more difficult to implement, if even allowed. The problem is apparent: at a certain wind speed, anything on top of the roof is going to start blowing off. That means raining dirt and debris from the roof should a hurricane or tornado come through. Luckily, there are still plenty of other rooftop options suitable for those environments.
Cool roofs are coated in highly reflective materials that can remain cooler than traditional rooftop materials during high temperatures. Cool roofs can unlock many of the energy efficiency benefits as green roofs at a far lower initial cost. Cool roofs are best suited for buildings on a budget, where the primary focus is savings, rather than providing usable amenity space. The downside is reflective materials will degrade faster than traditional materials, meaning that replacement costs are higher than green roofs. A large number of buildings already have cool roofs or at least some attempt to reduce the sun’s effect, using light shades of building materials that can reflect heat instead of absorbing it.
Solar panels are an increasingly popular option. These days, solar panels come in all shapes, sizes, and efficacies, even transparent glass. The benefits of solar panels on the roof are two-fold, they generate electricity and provide a level of shade. A building can use solar electricity to offset demand or even sell it back to the energy provider during peak hours with the proper equipment. Panels can be weighed down via ballast on roofs capable of supporting the weight so the roof isn’t punctured or fully attached to the structure.
As solar technology rapidly advances, panels will become more efficient, increasing the return on investment for owners. Clever designers are devising ways to have the best of both worlds: solar panels and green roofs. Benenati’s company Furbish is the perfect example. Using innovative racking methods for the panels, the company can install solar panels above the green roof, allowing light and water to reach the vegetation beneath via the necessary slanted angle of the panels. Benenati said the combination of solar panels and green roofs has reduced some clients’ ROI from seven years down to three.
“We always ask, ‘What do you want of solar?” Benenati said. “Is it to maximize electricity? That’s not always the case. High-efficiency modules can cost nearly twice as much. Buildings can get midgrade, which doesn’t maximize electricity but has the lowest cost per watt. Or do you need credits for certifications? Different clients want different outcomes, it’s always important to ask.”
Rooftop honey bees are becoming a popular option among building owners looking for low-hanging fruit to improve the roof. Just like HVAC, beehives benefit from being above the action where they go unnoticed and untouched. Housing a lightweight hive hardly requires any work, they can be weighed down with cinderblocks and beekeepers will be by to do any necessary work. Urban beekeeping is becoming popular in major cities. Don’t worry about height, bees can travel several miles in the search for sustenance, making a few hundred vertical feet nothing to worry about. More than 2.98 million honey bee colonies are registered across the US, with tens of thousands on rooftops, according to the US Department of Agriculture. A beehive is even humming atop the White House.
Working with telecommunications providers is a profitable, albeit less nature-focused approach than bee colonies. Rooftop leases for telecom equipment are a common practice, using the height of the building for better and wider signals. A wide variety of communication methods ranging from, cellular antennas to fixed wireless services, pagings services, and mobile radios all work with building owners to lease rooftop space for equipment. Providing space for telecom equipment on the roof can be a serious source of extra income. Rooftop telecom leases have been proliferating for decades and the coming adoption of 5G cellular technology, which needs more towers in closer proximity, means that more and more buildings will likely have antennas installed soon.
Rooftop entertainment venues and event spaces are some of the most sought-after places in any city. Spectacular views of the urban environment make a fine pairing with practically any activity. Summers in Chicago, New York City, and other cities are often enjoyed from a rooftop. Rooftop Cinema Club is bringing movie screenings to skylines. Rooftop venues can be major moneymakers, making even more than ground-floor retail. The biggest challenge is managing access to the roof. Upfront costs are steeper because safety measures like guard rails must be installed. Elevator access and traffic from the ground floor to the roof can also be a challenge. Finding and working with entertainment tenants on expensive build-outs and maintenance can also complicate matters, making rooftop venues best examined on a case-by-case basis. If public access or entertainment venues are out of the question, charging photographers and influencers for rooftop access can also be a source of ancillary income. The property staff can accompany approved individuals on the roof as they take pictures or post on social media.
Because of rooftops’ unique place atop our beloved buildings, they have special potential. Using rooftops just to house HVAC equipment may be a sensible decision, but it could be leaving opportunities on the table. Taking a closer look at what your rooftop is doing for your building and your buildings operating income will serve practically every owner and building manager well. A great roof can top off your building—and your balance sheet.