As green remodeling is by its nature limited to making improvements somewhat piece meal, the opportunity to build green from the ground up is a wonderful opportunity to take a holistic approach that opens the doors to a full range of sustainable design and green building techniques.
Because this project called for a new custom home rather than a remodel, it provided us a dream opportunity as green builders. We were able to fully integrate a key principle of sustainable design & green building: sustainable site design.
Sustainable Site Design Principles
For this project we were able to
- Conserve land through infill development and use of existing lots
- Preserve green space and wildlife habitat through efficient site development—make the most of a reduced footprint
- Protect the local eco-system by employing landscape design that a) controls storm water run off from roofs and b) uses permeable surface materials (for walkways, patios and driveways) that allow water to percolate naturally into the ground
- Orient the building to take full advantage of natural assets such as passive solar energy, shade trees, day lighting, and natural ventilation.
In Sustainable Design Form and Function Are One
There are two aspects of this custom green home that perform as one, but for the sake of clarity we’ll look at each separately. First we’ll look at how a sustainable design approach made it easy for this new home to co-exist with the natural setting. In the second half of this case study, we’ll consider the inner process: how those embedded principles of sustainable design gave the home its one of a kind architectural integrity.
A House That Cooperates With Nature
Our new house was set on an urban infill lot and we designed it to fit the context of the site. The lot backs up to the Sligo Creek Park stream valley. The Sligo is a lovely meandering urban waterway that shelters bicycle and walking trails along its tree lined embankments. Streams (including the Sligo) and rivers in the Maryland and Washington DC region have already taken a beating from storm water run off due to intense development. So on site storm water management was an imperative.
Landscaping and sustainable site design were integrated with building design from the start. Porous material is used in the driveway and walkways. Abrams designed a brick pattern and underlayment for the driveway that enables it to manage a large portion of run off from the roof. Other downspouts drain to various rain gardens in the yard.
The building is oriented to take advantage of the natural assets of the site. The house is set front to back on an east to west axis with the back of the house overlooking the forested stream valley. There are large windows on the south wall and minimal windows on the north.
The yard slopes steeply toward the creek and the terrace level faces east—the cool shady portion of the lot. Large patio doors open to a screen porch there, drawing in cool air from the shaded stream valley.
A few steps away from the patio doors, at the center of the house, the stairwell functions as a thermal chimney. Three short landings between floors lead to the top where mechanically operated roof windows evacuate hot air from the upper floors. This simultaneously draws cool air upward through the core of the house to displace the escaping hot air.
Energy Efficiency Features
Our building envelope is wrapped with a vapor barrier and insulated with spray foam to eliminate heat transfer associated with air movement. This airtight construction requires mechanical ventilation to draw a constant supply of fresh air into the house. We chose an energy recovery ventilation (ERV) system. In winter the ERV extracts heat from the stale air that is being exhausted to the exterior. That heat is used to equalize the temperature of the fresh air being pulled into the house. This means that less energy is expended to bring incoming fresh air up to the indoor temperature setting.
Building Green Is Building Beautiful
So we’ve covered the ways that the green attributes of this house determine how it functions. Now we will consider how this functional strategy is responsible for the pleasing look of the home.
The underlying theme of efficiency plays out as a rational, orderly and simple aesthetic. At a glance, the building is defined by forceful bilateral symmetry—the most basic of geometries. The theme relies on triads throughout. There are three large gables, three equal sections under the front porch, and a tri-part rear porch.
On the interior, three equal structural bays divide the zones of each living area on each floor. Openings are grouped in threes: the gable windows, the three principal openings between living and dining areas, three skylights in the loft, and the tripartite motif of the stair rail.
In terms of architectural traditions, the house on Park Crest reflects the designer’s struggle to get free from historical styles. The design employs traditional details but attempts to reduce them to an essence or eliminates them wherever possible.
The principle elements of the house—the gables, valleys, hips, and overhangs—are a synthesis of several related architectural traditions. It pays homage to the Irimoya roof form (a low pitched gable roof supported by a sheltering hipped apron) and its most beautiful expression, the Katsura Imperial Villa in Kyoto, Japan.
Our gables are more energetic than Katsura. The high roof ridge and the steep pitch provide more living space on the upper floor, but also reference the Minka dwelling, a Japanese folk style featuring the steeply pitched gassho (“praying hands”) roof .
So, as we look once again at the Park Crest home we see that the differing masses talk nicely to each other. There is a dialogue between twos and threes in the component parts of the structure. The intersections of the crisp 45-degree roof planes are suggestive of origami.
Sustainable Design and Green Building Continue To Evolve
Compared to a conventionally built home, our house is at least 50% more efficient than a comparable code compliant new home built the same year. In the interim, the Abrams approach has evolved significantly. Were we to build that same home today, it would be 100% more energy efficient and cost about 5% more. But we think it would also be approximately 105% more beautiful to look at.