Friday, March 28, 2014

Permeable Paving

By Tyler Hermanson, with contributions from Chris Higgins

Permeable paving is the approach of creating driveway, sidewalk and patio areas that allow water to pass through recharging the ground water and providing usable water to plants and trees. Outdated building practices paved everything, spurring statements like Joni Mitchell's, "they paved paradise and put up a parking lot". This was easy, cheap and created fair durable, fairly easy to maintain surfaces. This also creating major problems, increasing the temperatures of cities and drastically changing how the land deals with rain fall increasing the likelihood of flooding due to storm surge.

Permeable surfaces can increase green space, cool temperatures and provided important water control during rains, charging the ground with water rather than overflowing streams and rivers. It can look great too.

In this article, we'll outline some of the options available out there.


Image from Hillside Stone
Option 1: Crushed gravel or stone

Advantages:
  • Low cost
  • Drains free, allowing ground water to recharge
  • Prevents all runoff
  • Typically locally sourced
  • Low energy intensity
  • Materials are reusable
  • Can be a DIY project
Disadvantages:
  • Clearing snow can be tricky
  • Some may not like the look

Image from Contracosta
Option 2: Strip driveway

Advantages:
  • Aesthetics, people like the look, breaks up a solid driveway
  • Works well for most vehicles
  • Prevents most runoff
Disadvantages:
  • Can feel narrow for motorcycles
  • Professional install recommended, hard for DIY

Option 3: Permeable Concrete

There are many styles of permeable concrete, here are two of them:

Image from Aqua Pave
Interlocking Pavers

Advantages:
  • High durability
  • Drains free, allowing ground water to recharge
  • Prevents all runoff
Disadvantages:
  • Can be expensive
  • Requires professional install


Image from Angelus Paving Stones
Turf Stone

Advantages:
  • Drains free, allowing ground water to recharge
  • Prevents all runoff
Disadvantages:
  • If filled with grass/plants they can be tough to keep green as they may dry out in summer months


Image from Scotia Eco-Living

Option 4: Eco Grid Type

Advantages:
  • Easy to DIY
  • Drains free, allowing ground water to recharge
  • Prevents all runoff
  • Often made from recycled materials
Disadvantages:
  • Works best with stones of some kind.  Using grass can be hard on the grass in the areas where a vehicle is parked
There are many other options out there.  Here are links to more information:


Option 5: Typical Concrete with slopes to manage water on-site

Using slope and on-site catchments, like cisterns and rain gardens, impermeable surfaces can be used to help keep rain water on-site where drainage to the storm system can be slowed or stopped

Advantages:
  • Inexpensive and typical to install
  • Provides durable finishes
  • Easy to clear snow
  • Easy to DIY in small areas
  • Wide range of colours, finishes and textures
Disadvantages:
  • Requires careful design and installation to keep water away from buildings, but collect and store on site
  • Some increase in costs if using a cistern system


Any of these methods could earn credit under LEED Canada for Homes for improving the permeability of the lot and controlling storm water.