Getting Grass on High

Those of you who have designed (or tried to include) green roofs in a project have encountered the three big obstacles:

1. Depth:
Plants need soil to grow, and plants of any size need even more soil. The thinnest systems ("extensive" type) that can support grasses or sedums are generally recommended to be 3 to 4 inches of soil. Additionally, the soil sits on a thick multi-layered system beneath: a filter fabric, a drainage/water retention eggcrate, a moisture mat, a root barrier, and finally the roof membrane - give or take a few layers depending on system.


2. Irrigation:
You went to all that effort - you want to keep it alive. The thinner the system, the quicker it dries out. Designing an irrigation system is necessary. Integrating it can be a challenge.

3. Weight:
You can imagine that the soil and plants will weight more than an average roof; now imagine it all wet and holding moisture. The added weight of a green roof needs to be accommodated from the start of the project, and translates into a beefier structural system with its added expense.

While most agree that a green roof is an excellent idea - slows storm water runoff, decreases urban heat island effect, looks nicer, absorbs CO2 and creates oxygen, increases wildlife habitat, filters contaminants, provides natural insulation, etc. - the effort and expense involved often sees a green roof disappearing midway through the design development.

Enter this new product (picture at top).
As Inhabit writes:
"the folks from Toyota Roof Gardens (a subsidiary of the Prius-creating car company) have solved your green roof installation qualms with a tile-based system that’s as easy as laying down carpet. The TM9 self-watering turf tiles measure twenty inches square, and connect directly to irrigation systems, making them entirely self-watering. And at a slim 2 inches thick, the tiles lightweight and do not require any additional structural upgrading to your existing roof."

While a grass lawn isn't necessarily as appealing as the variety of plants one can grow in a thicker system, it's still nicer than a roofing membrane. My follow-up questions would be:

• Does the super thin system then mean that it dries out very quickly requiring a whole lot more water than usual?
  
• How water intensive is the grass variety itself? Sedums planted in traditional systems can survive dry periods and require little water; must the grass be always kept moist?
• If a small patch dies, how difficult is it to replace?
  
• Does the grass require fertilizers or other special food or chemical products to keep it happy?

Now the next challenge comes in the form of designing in the fall restraint system for you and your lawn mower...