There is no doubt that green roofs offer significant environmental benefits on several levels; just ask planners and builders across Europe, where green roofs have been popular for decades.
Evaluating Your Options
When planning how to develop a particular parcel of land, the first consideration is what function that land is best suited for. For example, it’s not going to make anyone happy to place a busy car sales lot in the center of a suburban residential area. Once the general goal is defined, it’s time to consider how the building itself will meet the needs of the business(es) that will occupy it. It’s a similar process when evaluating the question of whether to install a green roof or pursue another option.
Understanding the goals (both practical and social) for a green roof will help shape choices at every step of the way, including during concept design, budget analysis, installation and maintenance. If the realities of a green roof don’t align closely with the goals of a particular project, it’s time to look at other solutions that are able to meet those goals.
There are huge benefits associated with green roofs, and some factors that may make them less than ideal, and we’ll cover them in the pros and cons section. Before getting started, though, take a moment to gather some initial information.
Roof Load
The first, and most important, consideration when contemplating a green roof is the increased load on the structure itself. An extensive green roof has a relatively smaller roof load, on average, than an intensive design. This factor may make a difference in your choices when you’re considering an existing structure. In the case of new construction, it may take only minor changes to support even an intensive green roof. Keep your ultimate goals for the green roof in the forefront as you make decisions about the type of roof and the expense of adding additional structural support.
Moisture Management
Green roofs will help a lot with stormwater management, but it’s still important to spend time understanding how the roof will change the patterns of moisture retention and water movement on the roof itself. For example, You don’t want water to pool above the waterproof membrane in the center of the roof. Potential problems can be addressed during the design phase, but it’s a mistake to leave that question until after the first rain.
Maintenance
No matter what kind of green roof you choose, you’ll still need to plan for regular maintenance; though the frequency and intensity of that maintenance will vary considerably. An extensive green roof can be essentially self-supporting once it’s well established, needing little more than a couple of visits a year to remove and replace any dead plants, top off the growing medium, and carefully inspect the structure for any damage or wear. Remember, however, that it’ll need more regular attention in the first couple of years while root systems are getting established and until the plants are able to out-compete weeds.
Intensive roofs may include anything from a broad lawn that needs regular mowing to a series of perennial flower beds with a path and a few benches. Obviously, the frequency and intensity of maintenance will differ according to the choices you’ve made. Keep these questions in mind as you weigh your options against the goals you’ve set for the space.
Be sure to plan for access to your green roof, whether you’ll need daily gardening activities or brief access just a few times a year. Even a mature, self-sustaining, sedum roof needs an occasional checkup.
