In cities, concrete, tempered glass, and steel dominate the street. Since the Industrial Revolution, these have been the materials of the urban environment. The mechanical properties and structural stability they provide make our current streetscapes possible. Tall buildings, underground utilities, and transportation networks have evolved through their strength. Yet these materials often leave people wanting green and open space; families often move to the suburbs to for a slice of yard. In our current age, challenged by population and climate, urban planners and architects have begun to re-evaluate how cities work. Can cities become more natural? Can they offer green spaces for relaxation, a canopy of trees, the rustling of wildlife? It’s time to take another look at the urban landscape and reconsider the balance of hardscape and organic elements.
What is hardscape?
Hardscape includes all hard landscaping materials. It contrasts with soft materials like vegetation and soil. Hardscape can include concrete, asphalt, stone, glass, brick, metal, and gravel. Outdoor walkways and roadways, pools and lined water features, patios, retaining walls, and gravel drainage areas are all examples of hardscape.
In general use, hardscape means materials placed by human design. Landscape architects and contractors working on outdoor green space projects are the pros that talk most about the placement of hardscape. Traditionally, the term has been used less often by urban developers and architects, who build so much out of hardscape that vegetation is often the addition. This is changing as a new generation of planners consider urban design. By thinking clearly about hardscape within the context of cities, we begin to unravel our basic planning assumptions. What is needed to bring nature back into urban areas? Natural venues are human venues. Human-centered design considers how nature can thrive within the urban setting.
Hardscape vs. site furniture
Some people include items like gazebos, benches, and planters into the definition of hardscape. Others would consider these items to be site furniture. The distinction is slippery because a lot of site “furniture” is bolted or embedded into the concrete, growing out of it as a permanent feature. Popular dictionaries do not provide precision: Merriam-Webster includes benches and gazebos, whereas the Oxford Living Dictionary (an online and less formal version of the OED) defines site furniture as man-made landscape features and structures, but does not offer specific examples.
French speakers know buildings as immeubles and furniture as meubles—unmovables and movables, respectively. In this sense, hard items built into a landscape plan are structural, not furnishing, as they don’t move. A bollard sunk into a concrete footing seems clear hardscape, as does a traffic bump or a curb. A bench or wastebasket is more often site furniture. It may be relocated, and is not part of the structural plan.
When we talk about rewilding cities and green architecture, most people imagine less hardscape and more plants. There’s a growing public appetite for greenspace. Since 2016, Google has seen a rise in people googling forest bathing. For the past twenty years outdoor elementary schools, said to combat nature deficit disorder, are popping up across North America. Increasingly, urban design includes ecological design.
Good research underpins this trend. Mounting evidence shows that green urban spaces relieve stress and make for positive changes in cardiovascular health. On a warming planet, trees provide carbon capture. Green roofs and trees clean and cool the air, fighting urban heat sink and scrubbing particulate matter. Trees protect biodiversity, manage rainwater, provide shade, and absorb noise. Property values are improved under a thick green canopy. People prefer walking on tree lined streets—and increasing neighborhood walk appeal means increasing opportunity for local businesses. Trees and their economic, social, and physical benefits are so popular they’ve given rise to a hashtag on urbanist twitter: #StreetsAreBetterWithTrees.
Most people see hardscape in opposition to the return of the wild. Yet urban ecologists who work to return nature to cities consider how the hardscape in cities echo natural landscape. Concrete is analogous to stone, and buildings form regular canyons with sheer cliff faces. Pigeons have shown us wildlife can adapt to human-made cliffs. By watching wildlife in natural structures, urban ecologists are coming up with strategies to help a greater diversity of nature settle in cities. This can mean adding green, but it also means tweaking the hardscape to be more inviting, so nature can find its own way.
In Britain, stony-field refugia on the tops of buildings are bringing back the black redstart bird. Similarly, green roofs, connected green space and wildlife corridors, butterfly and bee supporting planters, and bat boxes are modern landscape features that invite natural elements to make their way into the city.
Metal in urban hardscape
Concrete, asphalt, and glass are the most common visible hardscape elements. Yet many of the functional pieces of hardware in the built environment are made of iron, steel, or aluminum. Sometimes, bringing nature back into cities means changing where this functional hardscape is placed.
Mostly at grade, and often invisible, the urban floor is covered in tree grates, water-draining trench grates, stormwater grates, detectable warning plates, manhole covers, bollards, lids, downspouts, and frames. Urban ecologists are viewing these elements in new ways to support sustainable design.
Water management and diversion—trenches and stormwater grates
Water management is one of the most important elements of a city’s hardscape-prominent construction. Cities are covered in water-impervious surfaces. Where natural landscapes usually experience 10% runoff, urban landscapes must manage 55% run-off. Municipalities must actively manage storm water to prevent flooding through the concrete heart of the city.
Further, the city’s run-off does not infiltrate deep into the soil to replenish the groundwater. It is often polluted after washing over buildings, roads, and sidewalks. It enters the sewer system filled with debris, pesticides, insecticides, and particulate. Often, this water is diverted to sewage treatment or emptied into natural waterways.
The capillaries of this water management system are carved and contained by hardscape. From the tops of buildings, eves and downspouts collect water and bring it to grade. On the surface, small trenches collect and direct water to larger sewer systems, like streams feeding a river. Each trench grate and sewer grate makes the hardscape more water-permeable. The placement of these items determines how water moves through the city. As cities invite nature back, it’s important to consider how these artificial waterways affect the water table and water cycle.
One sustainable strategy is to install bioswales, or rain-gardens, which collect water into living areas. Plants and strata of soil and gravel beneath them do the work of filtration, recharging the groundwater. These bioswales are often fed by trenches which once would have drained into the sewer system. A change in the organic profile of the city is supported by a change in the position and intention of the hardscape waterways.
Bioswales are non-pedestrian areas: too many feet walking through them will compact the soil and make it less effective. In some environments, the movement of people and traffic remains important. In these situations, long stretches of sidewalk can be replaced with a tree grate array. It is walkable, but permeable. The soil below grade can be dug on angles to help run off drain into tree roots or bioswale. This change allows for greater run-off capture while preserving walkability. Since a trench offers only a small surface area, these tree grate arrays also offer water capture over greater space.
Streets are better with trees… and tree grates
One of the issues affecting trees and other plants within a city is the stress of the city itself. Human stress is lowered among trees, but the same cannot be said for trees in the city scape. Some trees are healthy enough when used as lonely sentinels on either side of a boulevard, but some will struggle and fail. Light, water, and soil are all challenges in a city. Impervious surfaces mean less water in the soil. Skyscrapers block the sun and keep trees in shadow for much of the day. Soils are not fed by rotting leaves and trees as they would be in a forest. On a busy downtown sidewalk, hundreds of footsteps over soil compact it until it is as hard and dense as cement.
With these issues, tree grates are not just nice-to-haves. For the health of trees, they are often a must-have. The hardscape must shift from solid concrete to permeable grating in order to support and protect the tree’s root system. How large the grate must be to allow the right amount of nutrients and water is dependent on location, climate, and tree varietal.
Other infrastructure support
Hardscape can be used to support natural elements. It is also there to ease people’s daily lives. A uniform environment supports those with accessibility issues: good streetscape design will stay predictable and regular.
Grates and grills should not impede or trip people with mobility issues. Hardscape provides stable ground to pedestrians, and an even surface to those using scooters, walkers, and wheelchairs. Detectable warning plates, sometimes known as tactical ground surface indicators, are bumps or strips that warn those who are vision impaired that there is a hazard coming up, such as a curb or intersection. Designs incorporating tactical indicators can warn against changing surfaces, like hardscape to soil.
Crash-ready bollards, walls, fences, and site furnishings provide security against vehicle impact. Low-impact versions define perimeters and guide traffic. These types of site furnishings and hardscape options may also be used to protect trees, bioswales, plantings, ponds, and animal habitat.
Looking at urban hardscape anew
The world’s population is increasingly urban. Sustainability requires us to rethink the ways urban places use resources. Bringing nature into the cities is good for both human happiness and long-term urban stability.
To make these changes, the components of the urban landscape should be considered as parts of an ecosystem. Big changes can sometimes come from small things. What can designers and planners do to create sustainable, accessible cities that foster community engagement and economic success? A new vision of urban ecology is arising, and small local hardscape changes, made many times over, can make a big impact.