Building a Seashell Driveway

The Before Picture

The Before Picture

My husband and I bought a distressed property in South Florida. The driveway was really distressed. It took an archaeology dig to figure out where it had been and what it had been. After a bit of detective work we found a ‘Chattahoochee Stone’ pea gravel drive with a turnaround in front of the house. About 70 % overgrown with apocalypse proof weeds. The front yard became a free for all ad hoc parking area. Nobody could tell where they were supposed to park.

Part of the reason we bought this house was the garage was in the back. This is unusual in South Florida. Garage doors are usually a dominant feature of the front of the house. In some places it seems as if someone got a gigantic copier and started printing out houses with prominent garage doors. Later it dawned on me the reason for this is to provide the least amount of stormwater running off the concrete paving (the shortest possible driveway) and given the flatness of the terrain, it was also a short run to slope the driveway to provide drainage back to the street. It is also the cheapest way to get a lot of houses on a piece of property (i.e. Making the developer more money)

My husband retired and we decided to forsake the traffic and cold of the big city and moved 600 miles south from Atlanta to South Florida. The namesake of our existing driveway material, the Chattahoochee River, is a major feature in Atlanta.  The headwaters of the Chattahoochee are in the North Georgia Mountains, then it winds through Atlanta eventually pouring out into The Gulf of Mexico on the panhandle of Florida.

The driveway needed a renovation, however, it seemed a bit ridiculous, not to mention wasteful, to import pea gravel 600 miles to South Florida. Additionally, I was not enthralled with the brown pea gravel, having found it to be a fiesta of weeds in my previous garden and it cost at least 3 times what I had been paying for it in Atlanta. Based on the appearance of the existing drive it was nirvana for weeds. Not a good idea in South Florida.

The search began for new material for the driveway. The local rock here is limestone; crushed rock primarily for road construction. The rock is lumpy, starts out white and eventually looks very dirty. I didn’t like this option, but it was cheap. My next thought was pouring a concrete driveway, but, as a Very well seasoned Landscape Architect  (yes, I meant to capitalize Very for emphasis) I could tell the drainage just wasn’t going to work. In the event of rain, there would be too much water running off the driveway with nowhere to go. With the exception of the floor of our garage, not a good plan.

The driveway needed to be made of a pervious material so the rainwater could soak back into the ground rather than running off. During the course of my concrete drive design/pricing exercise I met a grading contractor who told me it was possible to build a shell driveway. What I couldn’t (and still don’t) understand was why there weren’t any of these driveways around. The only answer is they went out of style. People had been seduced by the evil brown pea gravel from the faraway Chattahoochee River.  I can only guess why. I did recall, however, over the course of my career people have waxed on romantically recalling the crunch of the pea gravel in their (perhaps very wealthy and with many yardmen) Grandmother’s yard.  This reminiscence is usually related to formal boxwood gardens in the Deep South. They never had to pull the weeds or pay for imported pea gravel.

I thought the shell was a great idea and, of course, did a bit of research. The shell used for constructing the driveway is mined about 20 miles north of my house. It is a byproduct of mining sand; five different sizes of material come out of the mine and are used for construction. The sand is used for construction and the shells are sorted out by size and intended use. My driveway is topped with ⅜” graded shell.

Shell driveways, properly constructed, last a long time. The construction method is as follows:

Grade the area and remove about 5-6’’ depth of existing soil. Compact the existing soil to receive the base material. Provide restraints around edges of driving surface to hold the loose driveway material. My driveway has pressure treated pine timber and Black PVC Landscape edging that act to hold the shell in place. I have seen drives edged with concrete curb or pavers set in mortar. This looks great and is, of course, a lot more expensive.

French drains were installed under the driving surface in areas where the water collects as it drains off the roof during a large cloudburst. Another South Florida peculiarity, no gutters, but some scuppers…you must cope with whatever comes off the roof, wherever it comes off the roof. Fortunately, I like rocks and Rain Gardens.  The drains were made from old solid walled laundry baskets with the bottoms removed then the contractor dug holes and placed them underground, filled them with gravel and topped the whole thing with filter fabric. The old gravel from the existing driveway was reused to fill the drains.

To build the driveway a 2-3” layer of crushed shell (this looks like coarse sand) is laid on top of the existing soil and pressed into place with a Bobcat. This is topped by a 2-3” layer of shell placed with a Bobcat and pressed evenly. The crushed shell course binds to itself and creates a pervious base layer. The shell course provides the driving surface. Maintenance requirements are spraying weed killer (I use the non toxic homemade vinegar solution) and raking it out every now and then. The materials firm up a great deal from cars driving on them and rain, but it is still a loose material.

I am pleased with the appearance of the shell driveway and it’s functionality. It drains perfectly and looks great. The shell also gives a great local, beachy feel to our property. And it looks really clean. It is also a very sustainable project, the majority of the materials arrived from within 50 miles of my house. The shell is a reuse product from a local mine. The driveway is pervious and most of the stormwater drains back into my property. I have two guest parking spaces and a turnaround for use when backing out of the garage. Pleasing the environment and me.

The Shell Driveway

The Shell Driveway