We just competed installing our landscape design for the first Passive Hause in Arlington VA. The concept behind the house is to use construction methods that aid in reducing the amount of energy required to heat and cool the house over the period of a year. Roger and Eric Lin, the builders, estimate that the annual heating and cooling cost for the owner for one year will be in the neighborhood of $400. As anyone with a traditional house knows, this is represents a huge monetary savings over what most of us pay per year for utilities. I know that my bills run around $1,600 per year for electricity and at least that much for natural gas to heat the house.
The secret to the energy efficiency lies in the thickness of the walls and roof, and to an air exchange system located in the attic.
The house also features a partial green roof over the garage.
When we were approached to create the garden design for the home we sought to not only create a killer design that would compliment the modern architecture, but to bring sustainable landscape design principals into the design as appropriate.
We decided that our focus towards creating a sustainable landscape design would be to do what we could to slow water runoff from the site. Slowing runoff would not only help keep water from flooding neighbor's gardens, but would reduce pollution by filtering the water on site, and would help the plants thrive by allowing rain water to slowly settle into the soil, providing water for the new plantings.
In many gardens you now see large "pits" where water is directed. Governments are increasingly mandating "rain gardens" on projects. These pits gather rainwater from the site, were it sits until it's absorbed into the ground. While this can be effective, they are far from attractive. The rain gardens can also take up a lot of valuable real estate, which is especially troublesome in tight lots such as those found in Arlington.
Our approach was a bit different. We allow the water from the roof to drop onto gravel where it has a chance to absorb into the ground. Water that can't absorb, especially in a hard rain, runs over the lawn to a collection box, (catch basin) where it enters and then flows underground, under the front walk, where it exits onto soil in a planting bed. The water will collect here for a while, until it seeps down and into a perforated pipe. This excess water is then moved slowly through the corrugated pipe until it exits again in a planting bed. At this point the overflow begins a 30' "flow" along the property line until it reaches a very small rain garden at the property line. The water loving ash tree (already on site) benefits from the added moisture here.
The idea is to slow the water, to allow it multiple points to be absorbed by the soil, to replenish the ground water, and, when it eventually leaves the property to be as free of harmful nutrients (nitrogen)as possible. Another benefit to this approach is that when less water runs off a site, less water enters the storm sewer system. Reducing the storm water flow helps reduce erosion in the streams around the house, reducing the silt load that reaches the Potomac after a rain event.
As designers we are committed to doing what is right for the environment every day. But, we are also very interested in finding ways that we can achieve an environmentally friendly design that looks amazing!
We think that we have achieved this at Roger and Eric's house at 4616 8th Street South in Arlington. It's on the market now; swing by the open house on June 15th and take a look for yourself.
Arlington Passivehouse, house photos