Why I'm Staking My Future on Holey Ground: a Story About Pervious Concrete

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By Lauren Wray

Recently I have become an impassioned advocate for pervious concrete. Heaven help you if you are stuck next to me at a dinner party or networking event, you will get my latest take on the newest iteration of ‘hardscape.’

"Why?" you ask, vaguely curious, and hopeful I will continue to pass the appetizers.

Let me tell you!
Well first, let’s define the term:
Pervious concrete is similar in strength, durability and most ingredients to traditional concrete. Its most notable difference, however, is that water goes through it!

But why on God's green earth would you want water to go THROUGH your concrete driveway?

Better question: why not?

When water goes through this stuff, say in your driveway or in a Target parking lot, it takes all the dirt and grime, the oil slicks and heavy metals from your shingles and filters them into the concrete, the gravel beneath and finally into the native soil below - the ultimate filter.

So when that dirty water is soaking into your driveway or Target parking lot, think where it is NOT going: into the storm drain, to that creek, finally into the bay, river or ocean, where it would meet other untreated non-point source water pollution and kill friendly nice things like fish or water plants.

Wow, why don't cities use this stuff?

I know!? The good news is, some do, and many more will start soon. More and more regulations are coming down from storm water management agencies, encouraging and mandating Low Impact Development measures that include treating and infiltrating storm water - something that pervious concrete does really well. If the entire parking lot of your dentist's office was paved in pervious concrete, all the water that fell on the desist office's roof as well as the parking lot could be absorbed and filtrated by the pervious concrete. It is basically like a paved retention pond. Since you can treat all your storm water with pervious concrete for Low Impact Development regulations, landscape designers can use whatever plants they like in the bushes around, because they don't have to plan for bio-swales or rain gardens, but they can if they like!

But is it strong enough to drive a truck on?

Sure, it wouldn't be very good concrete if we couldn't drive on it. The current mix designs (concrete chemistry) are very strong, very porous and very durable. There are some amazing specs out there on some proprietary mix designs. I can send you details and in the meantime, here is a great video of strength and infiltrationtesting.

So, how much does it cost?

That is always the 'gotcha question' but luckily, due to slight differences in the type of materials and techniques that are used, the cost increase is nominal around 10 percent more than a traditional concrete installation for most installers. Price varies to your geographical location, materials available, etc, but generally it is a nominal increase. Here is a graphic that illustrates relative price points. In some large scale projects, pervious concrete will save money and project time because the job will require no drainage systems, very little grading, and reduced curbs - the entire parking lot is the drain! Wild right!

A world without curbs:

At this point, I consider us friends, and you may be at least more interested in pervious hardscape than before, and I have passed the crackers.

So tell me about you!

-- Lauren Wray
A pervious concrete enthusiast,
a part-time employee of Bay Area Pervious Concrete,
a Presidio Graduate Student &
an occasional monopolizer of conversations