Permeable Driveway and Walkway Construction
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Permeable Driveway and Walkway Construction |
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In the following table I compare characteristics of different surface materials in regard to their ability to let surface water percolate. Additionally, I compare a simple, one-layered base to a base consisting of 2 layers, one of which is crushed stone. The comparisons are based on my personal observations.
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Base Materials: Surface Materials: |
sand/stonedust bed (usually 2-3" thick) on original soil (1 layer, pedestrian duty) |
sand/stonedust bed (2-3") on crushed stone (4-6" or more) (2-layers, heavy duty) |
| gravel or peastone | peastone layer (usually 1/2") installed on base of sand/stonedust (ca. 2-3"): drains well if sub-soil is permeable; light duty only for pedestrian traffic | peastone layer on stonedust on a base of 3/4"-crushed stone (layer of 4 to 12" typical): fast water infiltration, usually light duty use only |
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Lawn with Turfstone (TM) or Ecostone (TM) (these are grit-like materials installed in a lawn) |
Turfstone installed on sand/stonedust base: light duty, can be used for occasional parking if sub-soil has a stable structure that can support the weight. Use might be limited to times when soil is dry, especially if the soil is slow draining. | Turfstone installed on sand/stonedust base on a drainage layer of 3/4"-crushed stone: very fast infiltration, can easily support cars, however, lawn will deteriorate with frequent traffic. Makes a useful overflow parking. The better (deeper) the base, the harder it will be for grass to get established. I also wonder if it would make sense to incorporate compost or some soil into the crushed-stone base for roots to grow in. There is somewhat of a contradiction between what a good driveway requires and what plants need! |
| Lawn with Flagstone tire Tracks | tracks need to have comfortable width; does not work well for curved driveway; otherwise an elegant solution. Large stones needed for stability, and installation has to be well done to avoid loosening of stones; drainage as good as surrounding lawn, which depends on soil characteristics | flagstone installed over a drainage base will improve infiltration, as well as stability of flagstone work |
| Brick | Infiltration is inhibited if brick pavement
has very tight joints. Therefore, use brick that has molded-in spacers or
use non-modular brick in a herringbone pattern. In this case, brick will
leave plenty of joints for water to drain through. Courser jointing sand
rather than very fine sand will also maximize infiltration. Brick should always be installed over a base of 3/4"-stone for optimum drainage and stability of the base. Above that is a layer of sand (with particles in different sizes from fine to course) as recommended by the American Brick Institute. Water infiltration and surface drainage are very good. |
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| Granite Cobblestone | Granite cobblestones are naturally very irregular, leaving plenty of joints between them - even if they are tightly set. I consider this the best surface for a permeable driveway. Just like brick, it should always be installed over a layer of 3/4"-crushed stone for drainage and stability. Cobblestone pavement can withstand the heaviest traffic and is more durable than any other natural or man-made paving material. Drainage can be maximized by setting cobblestone in a mix of 3/8'-crushed stone (50%) with stonedust or sand. | |
What is better: Sand or Stonedust?
Usually, Sand or stonedust are used as a bed to set brick or pavers, and they are also used as a base for peastone or gravel paths. In my experience, stonedust packs well and makes a durable base for all kinds of pavers and surface materials, however, it is not easily permeable by water and can block infiltration. Sand, especially course sand or a concrete sand mix, has good drainage properties, but it shifts easily and therefore is not usually a good base for pavers, and it is unsuitable as a base for peastone. I used a mix of the two materials for granite cobblestone installation, and it seemed to combine the best properties of the two. The stones would set tightly without shifting, and the blend would still have good drainage characteristics.
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