Thursday, September 8, 2011

water, too much

Paul Manogue, Somerset, NJ, August 28, 2011
While writing about how to protect the house from mold, we started thinking about the eaves of our house, which, at two feet deep, are meant to keep water away from the walls in order to prevent mold growth on the outdoors surfaces of the building. Eave is one of those architectural terms that has broad metaphorical and legal implications. We still use “eavesdropping” to describe furtive acts of listening in, for example. And in legal terms, stillicidium – the word Vitruvius used to denote the edge of the roof which casts rain water away from the building below – is also a legal principle dating to ancient Rome that states a landowner can only build in such a way that his house (or other buildings) do not shed rain water on his neighbor’s property, thereby maintaining the utility and value of the neighbor’s land.

We need to work better at understanding how the principle of stillicidium works at a larger scale. In much of the United States, we  have paved so much of the landscape that it prevents the ground from absorbing rain water. Instead, we direct the rainwater into storm drains which, in turn, dump the water into existing streams and rivers. The additional water volume multiplies as it proceeds downstream, creating or exacerbating flooding in older urban centers. We witnessed this phenomenon firsthand while living in northern New Jersey in the 1990s and early 2000s, and researchers have studied the problem for at least fifty years. In the last two weeks, the extraordinary rainfall from Hurricane Irene caused extreme flooding in these areas, and while this is not due solely to development upstream, clearly our pave-and-drain mode of suburban development is causing enormous damage. This can probably only be accomplished with region-wide planning covering whole watersheds.

At tin box, we’ve exceeded the drainage and paving standards of the local statutes in several ways. As much as possible, we’ll divert rainfall on the roof to the rainwater cistern (to filter for potable use) or hold it in the vegetated areas of the roof (something we’ll install in phase two). We’ve reduced the ground area given over to paving (to about 72% of what’s allowable), and where paving is unavoidable we’ve made it permeable, in order to allow rainwater to percolate into the ground. No water should end up draining away from the site.


  1. I have always been intrigued by these seas of asphalt that are in front of the Targets and Home Depots of the world. Even if rooftop parking (a logical solution in most cases) becomes too costly, the least we can do is pave these parking seas with pervious paving to avoid runoff. It would seem that there are other solutions that may even be cheaper than asphalt that we can use instead, but changing the norm always seems to be a monumental challenge in most situations.

    Changing this status quo doesn't really require innovation, as I'm sure a variety of products already exist. Designers and contractors need to collectively push clients toward other options, and municipalities need to change codes to push alternatives.

  2. You're right on all counts, Laura.

    One solution may be economics. Bill McDonough says that when he pitched the execs at Ford on the vast vegetated roof at their new truck plant, he simply argued that it would eliminate enough run-off that they wouldn't need to build a $20 million water treatment plant. Ka-ching. At least that's the story he tells.

    I suspect that better zoning and region-wide legislation are going to be necessary.