Archive for February, 2009

Designing Permeable Paths

Sunday, February 15th, 2009

   There are many ways to deal with permeable paths including manufactured pavers, gravel, and a variety of plantable grid systems. Lets remember that the operative words here are “permeable” and “pathway”. Permeable means: That can be permeated or penetrated, especially by liquids or gases: permeable membranes; rock that is permeable by water”. (http://www.thefreedictionary.com). Using this definition, water has to flow through the path to some extent, meaning there are limits to the compaction beneath the path, and it cannot be mortared. The other factor to consider is how will it be used? How finished/flat/accessible will the path be?

   On the inexpensive side, a gravel path, will meet many requirements, and last if well installed. It is important when installing gravel paths that the gravel be kept from mixing with the soil beneath it, or it will eventually become muddy. You will want to install landscapers fabric below the gravel, and some form of gravel retention (edging, brick, railroad tie, etc) on the sides. In the middle range of expense you have concrete pavers and grid systems like drivable grass (http://www.soilretention.com/drivablegrass.html), and turf protection grid (www.terrafirmenterprises.com). Concrete pavers on the higher end have aggregate mixed in that give them a stone-like façade and most important, they interlock without mortar. To find a variety of these products go to www.paversearch.com.

  The grid systems mentioned above allow plants to either grow on top of them or through them while supplying a firm path base. While this can be grass, it could also be sedums and/or other succulants. These can be used in combination with stepping stones.

On the high end there are paths made with real stone like cashmere slate, and in fact you can use any hard flat stone like granite, bluestone, etc. that is available as long as the base is not overly compacted and you don’t mortar the joints. Normal compaction on a walkway is 95% on a stonedust, item 4, or sand base, leaving little or no room for water movement. The alternative is to use a 3/8” base which will have more air space and allow more water movement.