How We Built Our Permeable Flagstone Patio

Shortly after we moved into our mid-century ranch style home, I visited my neighbor’s backyard and fell in love with her brick patio. From then on, I envisioned how beautiful and inviting our backyard could be if we were to pave our patio area. Last summer I finally pulled the trigger, and this summer we finally finished it and are thrilled with the results. In this blog post, I wanted to document our process for others who might be considering a DIY permeable flagstone patio.

What it Looked Like Before

Here’s a photo from the real estate listing of what the patio area looked like when we bought our house in 2021. You maybe can’t tell from the picture, but the fire pit was made of cheap retaining wall bricks surrounding a rusted fire ring, and it was falling apart and covered with melted plastic. The stone and mortar surrounding the fire pit looks cool in the picture, but it was so uneven and you couldn’t really set chairs on it. We knew right away that at some point we would want to replace the fire pit at least.

Drainage Considerations

One of my hesitations with a DIY patio makeover was that I didn’t want to cause a problem with drainage. Our entire backyard is a hill sloping down toward our house, and there was a ditch along the rock wall surrounding our grass patio that diverted most of the water that would wash down any time it rained. I was afraid that if we installed a traditional patio, with a sand bed and polymeric sand between the joints, we could potentially cause our house to flood, something our neighbors told us had happened in years past.

After extensive research, I decided the solution was a permeable patio. I designed a drainage system modeled after this diagram I found on the website of a company that sells permeable paving materials:

I also installed a system of French drains to carry the water coming from our downspouts away from our house and out of the patio, modeled after this diagram:

The Excavation

Since dirt moving is not a skill I possess, I hired our friend Alex Lopez to do this part.

The tricky part was calculating the correct fall to allow the water to flow downhill and away from our patio. The recommended fall is 1 inch for every 6 to 8 feet. We calculated the depth at the high end of the patio at 6 inches to allow for the height of the flagstone and the gravel beneath. In retrospect I think I would have dug even deeper to be extra safe, because gravel is cheap, but after a heavy rain 6 inches seems to be fine. Due to the length and width of our patio, the deep end was about 14″ inches, if I recall correctly. Thankfully, Alex is an expert excavator and was able to use a laser level to get the slope right.

After Alex dug out the patio, I installed the drainage system. Under each downspout I placed a catch basin, and perforated corrugated pipe carries the water downhill. The perforated pipe allows water to enter through the holes while simultaneously diverting water as the path of least resistance.

The white pipe along the house is an old French drain installed by a previous owner, so I just left it in place. Just before spreading 3/4″ gravel, drainage fabric was added on top of the dirt and under the pipe. This prevents dirt from mixing with the gravel while still allowing water to pass through.

The next step was to fill the patio with 3/4″ gravel, allowing enough space on top for the height of the pavers. I let Alex do this part too. He used a skid steer to move the gravel from my driveway to the patio, then spread it around using a concrete placer.

And this is how it looked for the next 10 months:

Getting a Quote from a Landscaping Company

At this point, I thought it would be nice if I could just hire someone else to finish the job. After all, I’d already done all of the preparation; all that was left was to lay the pavers.

I called a landscaping company to ask them for a quote, and they told me that if they were to do the job, they would have to remove all of the gravel and drain pipes I had already put in and redo it to make sure everything was done right, and they would not be installing a permeable patio. Their quote for the whole project was over $30,000.

That was not an option, so I decided to carry on with my approach of doing as much of it myself as I could and hiring hourly workers to do the parts I couldn’t or didn’t want to do.

Adding Pavers

Fast forward to July of 2024, when Josiah and I spontaneously decided to sell our house and knew that in order to get the best price for it, we needed to finish the patio.

At one point, we had considered using brick pavers, after seeing this beautiful Chinese courtyard at the Metropolitan Museum of Art in New York City:

I didn’t realize it would be so difficult to obtain permeable pavers. The brick pavers sold at home improvement stores are not made for permeable patio applications, because they don’t allow for enough space between them. I could only find one company locally that could special order permeable brick pavers.

But the real reason we ultimately ended up choosing flagstone instead of brick was that at the point we decided to sell our house, we felt like we wanted to get the patio done as quickly as possible, and flagstone just seemed easier and more accessible. We ordered five pallets of flagstone from a local supplier and scheduled the delivery.

The Substrate Under the Flagstone

Before putting down the flagstone, we added a 3″ layer of 3/8″ limestone gravel. The purpose of this layer is to act as a bed for the flagstone that would still be easy for water to pass through.

This time we were planning to move and spread the gravel ourselves, and I had even schedule a Dingo rental, but once again when I compared the cost of hiring someone to do the job to the cost, time, and effort it would have taken us to do it, I decided to hire another guy we know, Wyatt Storm, to do the job.

Laying the Flagstone Pavers

Josiah and I started this part of the project with a lot of enthusiasm.

We set up string across the area we were going to be paving to mark the height of the surface, and excitedly started placing stones. Figuring out how to fit them together and finding the perfect stone for oddly shaped spots was a bit like solving a giant jigsaw puzzle.

But as it turns out flagstone is HEAVY. Many of the pieces were well over 40 or 50 pounds. And not only do you have to lift each piece to put it where you want it, you also have to lift it a few more times to reposition it and level it.

After working on the project for several hours in the evening two days in a row, by the third day our backs were aching and our muscles were so sore that we had to take a rest day. And this was the amount we had got done:

At this rate, we realized, it would take us weeks to finish. With an upcoming vacation, we again decided to look for some outside help.

I posted the job requirements in our city’s Facebook group, and by the next day I found someone with previous experience laying flagstone who was willing to work for an hourly rate. He brought along two helpers, and the three of them had the project finished in a little over a week.

After everything else we had already spent on the project, I considered this additional expense money well spent.

Adding Gravel Between the Pavers

After the pavers were laid, the last step was to fill the spaces between them. We decided to use decorative pebbles for this purpose. We chose a size of gravel that was large enough that it wouldn’t easily blow out with a leaf blower (since our patio is a sea of leaves in the fall) but also wouldn’t leave large gaps. Josiah and I actually did this part of the project ourselves, transporting the gravel with a wheelbarrow and smoothing it between the cracks using a push broom.

Cost Breakdown

In case someone reads this because they are considering a similar project, I thought I would list out our exact expenses.

First of all, the total square footage of our patio is around 915 square feet. It’s a big patio. (Almost as big as our first apartment!)

Here’s what we ended up spending on everything:

• Materials for Drainage System: $257
• Drainage Fabric: $259
• 3/4″ Limestone Gravel + Delivery: $340
• Excavation and gravel fill: $5,500
• 3/8″ Limestone gravel: $500
• 3/8″ Limestone gravel fill: $850
• Flagstone + Delivery: $2,953
• Flagstone installation: $1,253
• Decorative Gravel: $155

Total Cost: $12,067

Not cheap by any means, but still under half of what I was quoted by the landscaping company! And, we know it will add value to the house.

Did the Drainage System Work?

I have to admit, I was pretty nervous for our first big rain, hoping all my planning and calculating was done right. I even had a nightmare that our patio overflowed and our house flooded!

The first time it was put to the test was before we had added the flagstone, during some flash floods in early spring. I nervously watched out our window as the patio filled with water…but the level remained more than 2″ below the concrete before it began to fall, just like I had planned. After the rain stopped, it took just 15 minutes before the patio was completely dry!

A few weeks ago was the first time we had a heavy downpour after the pavers and decorative gravel were added, and once again, I breathed a big sign of relief, as there was no standing water whatsoever, even while the rain was coming down the hardest. The patio did its job!

The Finished Project

We are super happy with the finished result. It is every bit as beautiful and inviting as I imagined, and we are trying to enjoy it as much as we can in these last summer months before we have to leave it behind.