Tuesday, June 9, 2009

Permeable Paving Solutions - exploring the options

As far as I'm concerned there are really 4 options for paving "green". Some, in my mind, are a lot less green than others. Only one looks really green. The others look more traditional. It would be - in my mind - a great thing to mix some of the options if we can't seem to rethink paving everything over entirely.

1. Grid - like EcoGrid or other grid systems - that has large spaces which allow the "green" to grow through. They are easy to lay down - at least EcoGrid is - and don't need special knowledge to install it. You can seed the grids with grass or use them with gravel. They are often made with recycled materials - in this case 100% recycled - but you have to check the specs. These grids act like a support structure for vehicles - distributing the weight. After a rains, the grids allow water to gradually absorb into the soil below.. watering the grass. Out of all the systems it seems the greenest... looks greenest. Can be installed by anyone who has master the fine art of putting together Lego.

2. Permeable Pavers = blocks of stone or brick - that can be laid out in a pretty pattern. They look solid but the water actually should flow between the blocks. Of course they don't look green, but they are what many people think of when they think of a permeable driveway. They can crack and shift a bit, and are more costly to install. I personally wouldn't install them myself.

3. Permeable Concrete. Well its a step up from regular old concrete! Again, it won't look as green as green can be. I've never actually seen it in use. Since the composition of permeable concrete is different it does require special installation. There is a great article here on pervious/porous concrete installation. There needs to be a lot of care with the ground prep and to quote the article on it "Because pervious concrete has a low water content, special attention is required during transportation and placement."

4. Permeable Asphalt - which for me falls to the bottom of the barrel of green choices. (sorry - that's a pun there since asphalt is scraped from the bottom of the barrels after all other petroleum-based products have been refined.) Despite the fact that its a better mix of materials its still ASPHALT. I am glad that it gets reused and all - but its still a step up from an impermeable surface. It looks more traditional - familiar - but asphalt is still ashpalt. Here's some great info on asphalt - what's that stuff . Not very nice. Not very green.


So lets talk about what you'd need to look at if you are doing a green or gravel driveway with option #1 - choosing the Grid to create a "greener" driveway.

Now I'm going to talk about what I know. About 7 or 8 years ago when I heard about grid use for parking lots it just seemed like an idea that wouldn't stand up. Plastic? Grid? What was wrong with a nice neat, black driveway like Dad had? It also seemed too radical. I envisioned something like plastic snow fencing, that could be rolled out, but that isn't what it really is like. (Well, there are some roll products which have their uses but if its for a parking application or walkway, or even a parking lot you'll need strength es).

Most grids come in sheets - large squares that allow you to lay them ontop of a gravel or soil/sand mix depending on what you plan to use them for. Most grass will need a few inches beneath a grid in order to grow. Some grass has deep roots - and the grass needs to grow through the grid and down into the soil to get established. The grid will protect the root base and act as a filter for rainwater. It doesn't matter if you place down grass or gravel - that layer acts the same way. Water seeps through into the base and then continues on its journey back into the ecosystem.

A few Important things to check for when you are looking at redoing your driveway and looking for grid:

#1. What kind of edge thickness does it have? If you plan on parking on it this will be an important factor. Ideally, if you have an edge, it needs to be reinforced - a bit of extra thickness that will make sure it doesn't slid/slip around. If you can pick up a sheet of a grid product and bend it - then think of what will happen when your car drives over it. So you need something with a bit of flex - BUT you also need to make sure it the grid won't splinter or crack when the cars turn or back up on it. Look for a grid with a good solid edge and you'll save yourself having to replace it.

2. Ease of Install:

Can you do it yourself or will you need to hire someone? This is the number one reason I think that EcoGrids are better than cement pavers. It costs a lot less ... and it won't cost a forturne to get installed. Personally, I would suggest a combination of both unless you like to shove dirt and gravel. A contractor can come in and regrade your surface, or simply excavate down a few inches. Another person will come in and dump the gravel. This part is suprisingly cheap. A small driveway can be excavated in a matter of hours. Someone who can run a bobcat will show up and be done quickly. Once the base layer is installed, (flatten it out too!) the grid goes down.

The diagram here is actually for horses = so the footing diagram shows a deeper layer. If you were putting down grass then you don't need such a high topping.

3. How Green is it? Is it recycleable? How much is made of recycled plastic? Personally, if I'm thinking green - I want to make sure it can be recycled - and has as high a content of recycled plastics as possible. Otherwise you're adding new plastic in. Rather defeats the purpose.

4. Does it crack or splinter? Can it be maintained like a regular gravel driveway

5. What temperature range is it designed for? If you live in the south or the north there's a huge difference. Is it environmentally neutral?

6. Is it available in different weights? Is there heavy duty stuff for trucks? Is there a light weight product? Is there a difference in how it gets used - is one for landscaping and one for driveways or is it all the same? What is the best weight for your application? For EcoGrid there are the technical specs available here.

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