Concrete sidewalks weren't designed with trees in mind. That's clear to anyone who takes a stroll down any tree-lined street, just about anywhere. Concrete sidewalks block the resources that tree roots need to grow and as a result, the roots grow higher up toward the surface. Eventually, they break through the concrete.
This causes obvious problems for the landowner, but it's also a major public safety issue. And it can be extremely costly to maintain sidewalks in places with abundant, large trees. Oftentimes, the choice comes down to replacing sidewalk or removing the trees (and fixing the cracked sidewalk). And oftentimes, the trees lose.
It was such a loss -- sidewalk-slicing ficus trees cut down in her Gardena, California, neighborhood -- that served as the impetus for Lindsay Smith to start Rubbersidewalks in 2001. She learned about a pilot project in Santa Monica in which rubber sidewalks were being tested as a way to prevent cracked concrete around trees.
The rubber sidewalks allow air and water to percolate down into the tree roots, which in turn grow thinner, less aggressive roots than trees hemmed in by concrete do. And as roots grow below them, the rubber sidewalks rise evenly.
Ten years and more than 140 installations later, the company now has three main products. The original Rubbersidewalk, made from used vehicle tires; Terrewalk, a second-generation version which uses a less energy-consumptive manufacturing process, has a longer lifecycle and is made from used plastic, and Verlayo, which is designed as an overlay for concrete areas and is used to make surfaces softer and safer for pedestrians.
I asked Lindsay for the low-down on these rubber walkways.
Smart Planet: How many used tires have been recycled into Rubbersidewalks to date?
Rubbersidewalks has diverted over a quarter million waste tires from landfill, mostly California waste tires. Terrewalks -- has diverted over a quarter million pounds of used plastic from landfills.
SP: How are Rubbersidewalks’ products made? Is the rubber heated and poured into forms? If not, how?
Rubbersidewalks is made with a method that is fairly traditional—crumb rubber (tires that have been chopped up into granules the size of sand) is mixed with polyurethane resin and colorant, put into a mold, then heated while compressed.
Terrewalks use a very different, and proprietary technology, in which plastic is spun around to release its heat, which causes it to soften. The pliable plastic is then molded under compression, without added heat. Terrewalks use what is considered a low carbon footprint manufacturing method.
SP: What's the cost differential between Rubbersidewalks products and conventional concrete walkways? The Washington Post said a project in D.C. cost three times more than concrete… Is that generally the case? If not, what’s the average?
We generally state that the initial install of Terrewalks may cost 1/4th more than concrete; Rubbersidewalks will probably cost 1/3rd more. Concrete is a lower cost material, but the actual costs of concrete are often ignored—or even unrecognized. Everyone has different factors, but in general we have found the real costs of installing concrete to be higher than anyone thinks. Of course, when it comes to return on investment we are hands down the greatest savings. Our products never break. When concrete breaks—something it is doomed to do when near trees or in freeze thaw climates—everything must be demolished and started over. That so called ‘lower cost’ is now doubled—often in less than 5 years.
SP: How much leeway, if any, do architects or designers have, in terms of what the product will look like or how it will function in a specific installment?
We love working with designers and accommodating their innovative ideas. Since our products can be cut, and made in different colors, many opportunities exist for nontraditional applications. Terrewalks in particular is a very multi-use product.
SP: What has the recession done to your company?
As everyone knows, the building and construction areas have been the hardest hit by the recession, and city budgets across the country have been frozen or reduced. Nevertheless, we have continued to grow the company. We grew by 25 percent in 2011.
SP: How many people are needed to install your products, versus the number needed to install a conventional walkway?
Our systems require fewer people than needed for conventional sidewalks…fewer skilled crew, less traffic control, zero waiting time, and immediately completed installation with no need to return to site. A significant cost (and hassle) savings.
SP: What about snow and ice? In what ways are Rubbersidewalks’ products different or the same as concrete in terms of ice build-up and snow removal?
Both Rubbersidewalks and Terrewalks are unaffected by cold weather, and can be salted and plowed without damage. Water that freezes on the surface before it can run off will turn into ice, as it would on concrete or asphalt.