Usually it is fairly easy to ensure a stone patio drains properly. Pitch it away from the house- making sure that sub grade drains away from the house as well, and the job is done. But sometimes the patio area is captured by garden beds, sloping yards and other land forms that make it hard to get water away from the home. I have used this drain design a handful of times to provide water with a path away from the patio.
The cobblestone/trench drainage system works off water’s tendency to follow a surface. The cobbles provide rainwater runoff with numerous opportunities to flow down into the pipe below and out into the yard.
A couple of things that help to keep the system working properly.
• Make sure you have a reasonable amount of slope in the pipe. Two percent works well.
• Keep the drainage material (gravel and pipe) free of debris and soil. Water needs to percolate through. That’s why you wrap it in filter fabric and put a sock on the pipe. Use a good grade of filter fabric. The plasticy stuff big box hardware stores sell for under mulch beds is not up to the job.
• Use white PVC pipe, not the thin-wall, cheapo, black corrugated pipe contractors favor. It’s crap.
• Put the holes in the perforated pipe down. The trench fills with water from the bottom up. As soon as it reaches the height of the holes, it starts to drain into the pipe and flow out.
• Keep the daylight exit clear.
Here’s a cobblestone system installed. Done right, it can provide an intriguing visual design element to a patio. This particular system begins and ends with grinding wheels. In this case the patio and cobble stones are sandstone from Tennessee. Cobbles are not necessary, though they do provide increased opportunities for the water to perc into the drain system.
I have installed similar systems at the edge of patios where grass or mulch beds have created puddles or soggy soil. The one pictured is in the center of a patio that is stuck between the house and a steady rising slope.