Design Workshop: How to Make a Home Sit Lightly on the Land
Piers, cantilevers, towers and more can help minimize a
home’s environmental impact on its site.
The site undeniably informs the building shape, how it’s supported, how it meets the earth and how sensibly the design reacts to local conditions. Sitting lightly on the land is a resilient strategy with economic, environmental, aesthetic and efficiency benefits for many building sites. Here’s how to determine if your project should sit lightly on its site.
Perhaps the most fitting image of architecture that sits lightly on the land is the tree house. This hotel room in Sweden is perched above the sloping land and sited to take advantage of its unusual position in the forest canopy. The structure hangs from four trees that act as columns.
There is appeal in the idea that natural drainage patterns, soil conditions and native vegetation can coexist with a building above. While this example is extreme, the concept can be applied to more earthly dwellings.
- Deal with uneven topography
- Preserve special site features, such as trees, vegetation and boulders
- Build on a floodplain, where solid foundations aren’t a sustainable option
- Conserve natural site drainage
- Utilize passive cooling in warm climates
- Adapt to a remote site or one with difficult access, where it is harder for equipment to excavate and construct a large foundation
- Reduce costs due to less site and concrete work
- Address rot, mold and insect concerns by eliminating the intersection with the ground
For homes that sit lightly on the land and minimize the impact on it, we’re most often concerned with how a foundation supports a building. This point of contact with the land can involve great expense, require rigorous planning and cause irreparable damage to the environment.
Traditional foundation types, such as the poured-in-place solid concrete, or slab, foundation, are often the default choice. They’re designed to distribute or spread the structural loads of the building onto the surrounding soil, but they’re expensive and environmentally destructive to build.
Eschewing the most common poured foundation, the designer of this home opted to reveal its foundation support and expose the columns. The building loads are collected into a series of points, and those point loads are transferred to the soil via a pier (or pier and beam) foundation. Set in line with the plane of the exterior wall, the columns allow the home to appear to be delicately floating above the land. The land is of a separate order than the architecture.
If you’re envisioning the classic camp in the woods with a tilting post foundation and uneven floors, think again. Modern post and pier foundations can be engineered to be every bit as stable as cast-in-place concrete foundations. It’s essential that they’re designed by a qualified professional engineer to ensure that the building loads are properly supported by the earth.
Making sure to properly air seal and insulate the floor is especially important with pier foundations to keep pipes from freezing and have a comfortable interior floor.
Piers aren’t the only means by which we can minimize the overall excavated footprint on a site. The cantilever permits floor plates to be extended to views and distinct site features without affecting the ground. This strategy works especially well to weave a structure in and around established vegetation — where, for instance, excavation would mean losing a tree.
Another effective design option is to build upward to reduce the impact on the ground. This tower rises from the dense forest understory to greet views and offer access to the natural light above. With two minimal walls supporting the tower, this design relies on structural efficiency to reduce site disturbance.
The bridge is a fitting device to minimize site interference; it brings to mind the engineering feats of the ancient Romans and their aqueducts or modern-day France’s Millau Viaduct. Spanning two heavier foundation elements, a bridge works well to preserve the natural site’s drainage patterns and flora. It concentrates loads at specific points. The foundation anchorages provide discreet locations for introducing buried power and plumbing infrastructure, as discussed previously.
Any of the previous concepts — bridges, towers, piers, cantilevers — can be combined to deal with especially complicated sites. Our building systems and materials are, for the most part, rectilinear. We’re accustomed to building and living in a planar world, and so it follows that our buildings are shaped by the materials we use. Sitting lightly contrasts horizontal floor planes against the natural land shape. The distinction between the organic and the manufactured lends each a special importance.
Perhaps the most obvious way for a house to sit lightly on the land is to minimize the size of the building. It can be difficult to separate our desires from our needs, and the process of designing a home intertwines the two. While I would like a two-car garage, a barn and a pool, having lived without them, I know they are desires rather than needs.