Up on the Roof

Like it or not, we’re all on the front lines of the environmental sustainability movement.

In fact, as shapers of water and land, few are in better positions than we are to make a difference, with many of us frequently working alongside architects, municipal officials and developers and being asked to design and implement green approaches that minimize a given project’s effects on its surrounding environs.

As I see it, this offers us not only a golden opportunity to shape the future of land development and architecture, but also to rise from our customary place near the bottom of the design/construction totem pole by providing compelling, well-considered and effective answers to environmental challenges related most significantly to water reclamation and filtration.

I’ve jumped into this arena with both feet just recently, and in the course of the coming year I’ll be using this space to share my trials, tribulations and, I trust, triumphs in these areas. Partly, my ambition is to cajole all of you into agreeing that this is a path you should watch and follow, but I also want to examine the realities, facts and figures and demonstrate that this pursuit is viable for (and valuable to) all of us in the exterior design/construction professions.

REACHING HIGHER

One of the most exciting things happening in our industry these days is the emergence of green roofs as a practical option. Literally, this involves treating a rooftop as we would a ground-level site (at least in design terms). With proper engineering, in fact, we can install all of the same things we might install at ground level up on rooftops, including decks, watershapes, cabanas and other structures.

This is, of course, nothing new, and “green roofs” have been around for nearly as long as civilization itself. The Hanging Gardens of Babylon, for instance, were among the Seven Wonders of the Ancient World; sod roofs have been in common use in northern climes for untold years; terraced rooftop gardens were in vogue during the Renaissance; and more than 100 years ago, innovative Germans started using rooftop vegetation to reduce fire risks related to the use of tar.

Heck, 30 years ago I myself spent a lot of time installing gardens on rooftops of high-rise buildings in New York, filling planter boxes with topsoil, small shrubs, perennials and even trees. Back then, it was meant to lend a grace note to urban living. Today, however, green roofs have been “elevated,” as it were, and have become integral, functional building features valued for saving energy and conserving and filtering precious water resources.

This reconsideration comes at a time when insulation, heating systems, waterproofing, ultraviolet-resistant membranes and fire departments are all remarkably efficient, so in the back of my mind I’ve long wondered why everyone’s so excited about putting plants on rooftops. What is the purpose? Is there really so great a benefit other than the trendy “coolness” factor?

As I’ve read up on things, followed the literature and basically found myself being pulled in this direction by clients and colleagues, I’ve heard all sorts of reasons why this is important – not the least of which is that I’m also being asked to create these special environments for use by people rather than to meet some practical conservation program.

In that light, I’m seeing these projects in a whole new way: These aren’t novelties or some passing trend; rather, this is a whole new frontier in exterior design and gives us access to a clientele that has long been denied the simple pleasures that come with walking in private or public garden spaces.

THICK AND THIN

Before we get into the details of current projects that have triggered this cascade of thoughts for me, I think a quick primer on the types of green roofs is in order. For simplicity’s sake, there are essentially two types of green roofs: extensive and intensive.

[ ] Extensive roofs are simple to install and in many cases can be retrofitted onto existing roof structures. (Before we get even a step farther along, I want to stress the absolute necessity of involving structural engineers at every step of the way in designing and installing even the most innocent-seeming green roof. Failures in these cases are often spectacular – and sometimes catastrophic.)

An extensive roof calls for only a thin planting medium, typically in the range of three to six inches, and finished weights in the vicinity (at most) of 50 pounds per square foot – an approach that makes the substructure much less critical. The tradeoff for light weight is a smaller planting palette, as you’re generally limited to using shallow-rooted types such as sedums and grasses.

These spaces can include sitting areas and other spaces for human activity, but the orientation is usually more practical and is focused on catching, filtering and recycling water rather than sending it to waste. Given the thin soil base, irrigation is needed in most parts of the country to keep the plants alive during the warmer or drier months.

[ ] Intensive roofs, by contrast, are more involved and costly to install. They start with a much thicker planting medium (ranging from minimums of eight inches and reaching depths of four feet or more in some cases) and are mainly installed over engineered concrete roof systems designed to support the extra weight of soil, plants, structures and water at levels that can approach 150 pounds per square foot.

The upside with these programs is that the plant palette is much wider: Very large shrubs and even trees can be accommodated. Proper irrigation and drainage systems are an absolute must with these installations, because no more than a carefully determined amount of (heavy) retained water can remain on the roof.

Membrane Longevity One of the concerns about green roofs is how long they last relative to surface systems used on conventional rooftops. The plain fact is, a properly installed green roof system, protected along the way from construction-related damage, will last significantly longer than a ballasted rooftop (that is, a liner covered with gravel). Even the lifespan of the least expensive membrane (that is, EPDM, which is typically guaranteed for 20 years) can be doubled. Moreover, many green-roof systems are installed using modular systems and planting trays, so in some cases the greenery can simply be lifted off the roof in the event liner repair or replacement is required. — B.Z.

This need to be weight conscious leads to use of many tricks to hold overall mass within tolerances. In many areas, for example, extruded Styrofoam insulation is used to build up areas where elevations are needed (and deep-rooted plants aren’t), such as on raised lawn areas. These and other measures are used to minimize the overall load.

Whichever way a project goes, the concepts of construction for both extensive and intensive green roofs remains the same: The roof surface itself needs to be waterproofed in one of a number of ways (using EPDM liners, spray-applied liquid rubber or coal-tar applications, to name a few) – the basic point being that this membrane is the most critical feature of green roof installation.

The applied surface must be flooded to test its watertightness, and a business has already grown up around testing these systems for leaks. Once the roof surface is leak-proof, the lining system is protected with a heavy geotextile atop which a drainage/water-retention layer is placed. In some cases, an insulating layer is next in line, but if it’s left out, installation proceeds with a root barrier (typically a woven fabric), then the planting medium, then the plants.

COUNTING THE BENEFITS

So now that we’ve rolled through Green Roofs 101, what does it all mean? Why is it of such vital current interest?

Already, a huge number of entire books have been compiled to answer those questions, but I’ll keep it short and sweet: Green roofs have tremendous insulating capabilities that result in substantial savings in the costs of both heating and cooling. These days, that’s enough on its own to have gotten the bandwagon rolling.

And the numbers are indeed impressive. In one Canadian study, for instance, it was found that a common, single-story building with a grass roof growing in slightly less than four inches of soil reduced summer cooling costs by 25 percent. Another study found that a six-inch, extensive-style green roof reduced heat gains by 95 percent and heat losses by 26 percent. And research on Chicago’s City Hall found that on a day when the outdoor air temperature was in the 90s and the black-tar portion of the roof warmed to 169 degrees, the half-acre planted portion of the same roof checked in between 91 and 119 degrees.

There have been numerous other studies as well, with all of them showing similar results. And not only do these insulating properties help reduce heating and cooling costs, but they also lead to another, less obvious benefit in that, in many cases, the equipment used for heating, ventilating and air conditioning can be reduced in size, thereby lowering initial costs, ongoing operational costs and other costs associated with installation of conventional insulation.

But there’s more, and this is where things get exciting for watershapers in particular: Beyond insulation, the main virtue of green roofs is their ability to aid in the control of stormwater runoff – an area in which watershapers’ familiarity with strategies for containing and controlling water come in quite handy.

Do It Right If you’re going to get involved with green roof development, take very seriously how you design and install them and surround yourself with tried-and-true manufacturers and advisers. Green Roofs for Healthy Cities (Toronto) has an entire educational curriculum available for anyone willing to take the time to attend their yearly conferences and ongoing sessions. I believe they’ve gathered the best manufacturers and installers in the world to teach and inspire. You might also take a look at Green Living Technologies (Rochester, N.Y.) and at Zinco, a German company with decades of experience: Both of them offer seminars and happily impart their wisdom on this very promising subject. — B.Z.

Especially in urban environments – and particularly with huge, warehouse-type buildings – the amount of water that can run off a rooftop during a large storm is significant and problematic. In many large cities, moreover, storm and sanitary sewers are interconnected and carry all water to sewage treatment facilities. In times of significant rainfall, these systems can be overwhelmed by the volumes of water running through them, resulting in diversion of the sewage portion of the flow to surrounding waterways. In my hometown of New York, for example, this means that raw sewage sometimes flows untreated directly in to the Harlem and Hudson Rivers.

With enough green roof development in urban areas, much of that stormwater can be slowed and/or retained by the vegetation and drainage layers, thereby significantly reducing the flow of water to the storm sewers. This is especially important in the first minutes of the storm events.

A few more numbers tell the story: In summer, green roofs retain from 70 to 90 percent of the precipitation that falls on them, while in winter they retain between 25 to 40 percent. With enough green roofs, we can help to alleviate the massive burdens imposed on combined sewer systems during rain events – and there are even proposals that will give property owners tax breaks or credits if their green roofs do not tie into sewers at all.

AND THEN SOME

Another huge benefit of green roofs is that they filter the water that falls or flows on their surfaces. With proper planning, the retained water can in many cases be used to irrigate the roof itself in dry times or maintain gardens at ground level. There’s also the possibility of using this “gray water” to flush toilets in the building, thereby reducing the substantial volume of potable water used for such purposes.

There’s more: Green roofs have aesthetic appeal, thereby making real property more valuable; reduce the heat-island effect; improve quality of life for employees who have access to these green spaces, thereby improving productivity; reduce sound infiltration; and provide space for recreation and habitats for birds and insects. In some cases, there’s also an opportunity for growing food – one of the many ways building owners can generate positive impressions about their properties.

In other words, green roofs have such a wide range of possible benefits that they give watershapers and landscape architects and designers who move into this specialty new types of projects to pursue and all-new stories to tell along the way.

In our case, we’re now working with officials in Rochester, N.Y., in trying to implement urban gardens on rooftops and in vacant lots in some of the needier parts of the city. Food production is, to me, a grand-slam no-brainer and an amazing opportunity. Just think: People can walk out their apartments’ front doors, take an elevator to the roof and pick a few tomatoes and cucumbers for that night’s dinner.

If for no other reason than to provide healthful food sources in urban areas, we should all explore the installation of green roof systems wherever it’s feasible.

Yet for all the virtues these rooftop environments encompass, it’s still tough to persuade property managers (especially developers) to buy into this concept. With more and more people looking to LEED certification as a selling tool, however, we can explain to them that a green roof will earn them credits in many categories – by reducing site disturbance, minimizing heat-island effects, managing stormwater flows, providing water-efficient landscaping, improving wastewater systems – and wowing everyone with innovation in design.

So far, much of the green-roof movement is being underwritten by municipalities rather than by private owners, but that will inevitably change as those very municipalities reap the benefits of these designs and eventually require them in local codes. As I see it, we watershapers and landscape professionals have a golden opportunity to jump in here energetically, aiding in water-conservation efforts while making urban life more pleasant for everyone.

For the moment these may just seem like cool, trendy spaces, but a time is coming when they’ll become commonplace for the good of the planet – and undoubtedly for our businesses!

Bruce Zaretsky is president of Zaretsky and Associates, a landscape design/construction/consultation company in Rochester, N.Y. Nationally recognized for creative and inspiring residential landscapes, he also works with healthcare facilities, nursing homes and local municipalities in conceiving and installing healing and meditation gardens. You can reach him at [email protected].