Permeable paving
Rain that soaks in where it lands
A normal paver driveway sheds water off the surface. Permeable paving does the opposite. The joints between the units stay open, filled with clean angular chip instead of sand, and rain runs straight down through them into a deep bed of washed stone. That stone bed is the reservoir. It holds the water while the soil underneath takes it in.
That matters here because Peninsula winters are wet in bursts. A few heavy days put more water on a driveway than the gutter out front can carry, and the overflow runs along the curb or backs up against somebody's garage. A permeable section keeps that water on your own property. It also keeps the surface usable while it is raining, because there is nowhere for a puddle to sit.
We build it to ICPI specification like everything else we lay. Finished, it can look like an ordinary paver driveway, or like open jointed stone set into low planting. The difference is all in the section underneath.
What is actually under a permeable paver surface?
Three layers of clean, open graded stone, and every load of it is washed. At the bottom sits the reservoir, No. 2 stone, which is big angular rock with large voids between the pieces. How deep that layer goes depends on how much rain the surface has to hold and how fast the soil below is willing to take it. It is the most carefully sized part of any job the paver crew takes on out of San Carlos, because it is where the water actually lives during a storm.
Above the reservoir goes a base course of No. 57 stone, then a thin bedding layer of No. 8 chip that the pavers are set into. The same No. 8 chip gets swept into the joints. Nothing in that stack is a sealed layer, so a drop of rain has a clear path from your shoe to the soil.
ICPI, the body that certifies our installers, publishes the specification this work is built to, and permeable sections are one of the places that specification earns its keep.
Why can there be no fines anywhere in the section?
Fines are the dust and fine particles mixed through regular road base. In a normal driveway they are the whole point, because they let the base lock up tight under compaction. In a permeable section they are the enemy. Fines fill the voids between the stones, water stops moving through, and the reservoir turns into a bathtub with no drain.
So every layer is washed stone, the joints get clean chip rather than joint sand, and we keep dirt out of the excavation the whole time it is open. We also leave the subgrade loose instead of compacting it hard, because the soil at the bottom has to accept water too. That is the opposite of a standard paver field on a closed base, and the two sections are not interchangeable.
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ICPI Certified Paver Installer. Family owned and operated, with a 20 year warranty on every installation.
Call (650) 705-0628Does permeable paving work on Peninsula soil?
It depends what is under you, and we dig to find out before we design anything. Sandy or gravelly ground takes water quickly. Heavy clay, which runs through a lot of the flatter neighborhoods near the bay including much of Menlo Park, takes it slowly and swells when it is wet, so the reservoir has to be deeper and hold the rain longer while the soil works through it.
Hillside lots in Belmont and Hillsborough are a different problem again. Water arrives from uphill as well as from the sky, and a permeable section on a slope has to be terraced inside, with check dams built across the reservoir so the water does not all run to the low end and sit there. Where the soil will not take the volume at any depth, we build in an underdrain and tie it into the same run that carries water off the driveway.
Why choose Exterior Designs for permeable paving?
Permeable paving is the one paver job where a shortcut stays invisible until the first real storm. Use the wrong stone, sweep ordinary joint sand into the gaps, or compact the subgrade out of habit, and the job looks perfect on handover day and drains like a sealed slab in January. We are an ICPI Certified Paver Installer and we build the whole section to specification, not just the part you can see.
Todd Chandler runs the crew, the business is family owned and operated, and we only work in interlocking pavers and natural stone. We lay Belgard, Calstone and McNear units, every installation carries a 20 year warranty, and estimates are free. Book a free on site estimate and we will open a test hole, watch what your soil does with water, and tell you straight whether permeable is the right answer.
Ask a paver installer
Straight answers about paver installation on the Peninsula
Does permeable paving clog up over time?
The joints slowly collect dust, grit and leaf litter. Sweeping the surface and vacuuming the joints every few years keeps water moving. If a section does slow down, the top of the joint is cleaned out and refilled with fresh chip.
Can I park cars on a permeable driveway?
Yes. The units are as strong as any other paver and the stone reservoir is built to carry the load. Tell us if a truck, camper or boat trailer parks there, because standing weight in one spot is harder than daily driving.
Will it look different from a normal paver driveway?
Only if you want it to. Permeable units have small spacers, so the joints read as fine dark lines that most people never notice. If you want the open look instead, we set slabs with wide planted or gravelled joints.
Do I still need gutters and downspout drains?
Usually yes. Roof water is a lot of volume arriving in one spot, so we normally keep downspouts on their own pipe. In some cases a downspout can discharge into the stone reservoir, and we work that out once we know the soil.
Does permeable paving work on a sloped driveway?
It does, with the reservoir stepped down the hill in terraces so each section holds its own water. On a steep run we also keep a surface fall and a drain at the bottom, because heavy rain always travels across the top first.
Do you install permeable paving outside San Carlos?
Yes. We work across the Peninsula and the wider Bay Area from our shop on El Camino Real, including Belmont, Redwood City, San Mateo, Burlingame, Hillsborough, Menlo Park and Atherton. Estimates are free and there is no obligation.