A gravel driveway is one of the most challenging to build on a slope. The gravel tends to slide downhill both during and after installation. You have to find ways to keep traffic and stormwater from eroding the driveway.
In this guide, we discuss how to lay a gravel driveway on a slope and how to keep the gravel in place for years.
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Pros and Cons Of A Gravel Driveway On A Slope
Gravel may seem like the worst material to use on a sloped driveway, but it actually has several advantages.
One, it’s cheap. If you are on a budget, a gravel driveway will cost you less (typically under $2 per sq. ft.) compared to concrete ($8-$18 per sq. ft.) or asphalt ($3-$15 per sq. ft.). Gravel is also cheaper than using pavers.
Second, a gravel driveway is highly porous and that’s great for drainage.
A sloped asphalt, paver, or concrete driveway can cause heavy runoff, causing erosion and flooding. That’s because these materials don’t absorb a lot of water.
In contrast, gravel allows water to easily sink into the soil. There is still runoff from a gravel driveway, but it’s not a lot and is usually easy to deal with using a swale or French drain.
A gravel driveway also offers excellent traction on steep slopes. You’ll be thankful for the gravel when it snows.
The biggest downside of a sloped gravel driveway is keeping the gravel on the driveway. This can make installation hard especially on extra-steep driveways.
It can also make maintenance expensive, since you may need to re-gravel the driveway frequently.
Thankfully, these issues are easy to mitigate using the right materials and techniques.
How To Build A Gravel Driveway On A Slope: A Step by Step Guide
A thick sturdy base, well compacted layers and adequate drainage are the most important things to keep in mind when laying a gravel driveway on a slope.
1. Planning & Design
The first step is planning and designing the driveway. This is where you decide where the driveway will go, how wide it will be and how long it will be.
It’s also important to measure the slope of the ground where the driveway will go.
Generally, you don’t want a gravel driveway that’s steeper than 12% (a fall of 12 feet for every 100 feet). If a gravel driveway is too steep, the gravel will keep shifting downhill and will be easily carried away by water.
If the area where the driveway will be is steeper than 12%, either find a way to reduce the slope of the driveway or stabilize the gravel to keep it from rolling downhill.
You can reduce slope by curving the driveway or adding switchbacks to it.
As you plan the driveway, don’t forget to plan for drainage. Figure out what kind of drainage you’ll use and where it’ll go.
2. Lay The Base
The base is the most important part of any driveway. Without a sturdy base, the driveway won’t last long under inclement weather and vehicle traffic.
A sturdy base is even more important on a sloped driveway. It’ll help keep the gravel in place and protect against potholes and ruts.
Experts recommend a base that is at least 6 inches thick. So you’ll need to excavate at least 8 inches into the ground. This creates enough space for the base and the gravel surface layer.
If you live in an area that receives heavy precipitation, consider making the base deeper to make it stronger and allow more water to absorb into the ground.
Here are some tips for building a strong gravel driveway base.
- When you finish excavating, compact the ground before you add any base materials. This will add strength to your driveway.
- Use a mixture of coarse and crushed aggregate in the base. It compacts really well to make the driveway extra-strong.
- Don’t pour all 6 inches of base material at the same time. Pour two inches at a time, then compact each layer before pouring the next one.
- When building the base, remember to maintain the grade of the driveway. And not just the slope from top to bottom, but also the right slope from side to side. Most gravel sideways have a crown design where the driveway slopes towards the sides from a high center.
- Lay a permeable weed membrane on the base layer. It’ll prevent weeds and grass from growing on the driveway while still allowing water to pass through. You can also lay the membrane at the bottom of the base layer before you add any materials.
You are now ready to pour the final layers of surface gravel on the driveway. But before you do that, install driveway edging.
Edging is very important on sloped driveways. It prevents the gravel shifting or washing off the driveway. You can buy ready to use plastic or metal driveway edging. You can also use blocks, bricks or make a concrete edging.
4. Lay The Surface
Most gravel driveways are finished with a single layer of decorative gravel. That works fine on flat and gently sloping driveways.
For a steeply sloping driveway, I recommend using two layers of gravel, each an inch thick. Use coarse gravel at the bottom and finer decorative gravel at the top.
Mixing the two sizes creates more friction, locking the two layers in place and reducing how much gets washed off.
For both layers, use angular gravel to improve its stability. Avoid pea gravel or smooth river gravel as it’ll easily roll down the slope.
Don’t forget to compact the surface layer of gravel.
4. Stabilize The Gravel
You can leave the driveway as it is. If you’ve followed all the above steps, you’ll have a strong driveway that resists erosion.
But, inevitably, some of the gravel will be carried away. Every couple or so years, you’ll need to pour more gravel on the driveway.
That’s why I highly recommend stabilizing the gravel even further using gravel pavers. These are grids that interlock and hold gravel in place.
They essentially create a solid driveway surface almost similar to asphalt or concrete. With gravel pavers, the gravel can last for years without washing away.
A gravel driveway with pavers is also much stronger, able to sustain heavier traffic without developing potholes or ruts.
To use gravel pavers, lay the base as usual then install the pavers on the base. Different types of pavers or grids have different installation methods, so check the instructions for whichever pavers you are using.
Next, pour one or two layers of gravel on top of the pavers and compact them.
Here’s a video showing the installation of gravel pavers.
We’ve also seen some homeowners stabilizing their gravel driveways with cement. You spread the cement on the gravel then lightly sprinkle it with water.
The cement hardens, holding the gravel in place.
Some issues mentioned by those who’ve tried this method is that the driveway can get a bit dusty when it’s dry (cement dust can be a health hazard) and that it doesn’t hold up well to heavy traffic.
I recommend using grid or gravel pavers. They last long, don’t produce any dust, don’t affect permeability and they can handle heavy traffic.
The final step in building a sloped gravel driveway is drainage.
There are different kinds of drainage options for gravel driveways. You can have a ditch on one or both sides of the driveway to take away water when it drains from the driveway.
You can also build a channel drain across the bottom of the driveway to collect runoff and redirect it elsewhere. Border the drain with concrete or blocks to ensure gravel doesn’t clog it.
Another popular and low budget drainage option for sloped gravel driveway is a swale.
A swale is a shallow and wide trench that’s filled with permeable material such as gravel. You can top it up with soil and even have plants on it to conceal it.
A swale captures water runoff, slows it down and lets it sink into the earth. It will prevent runoff from reaching your home or the street.
How To Maintain A Gravel Driveway On A Slope
Keep an eye on any potholes that start to form and fix them immediately. Small potholes can quickly widen especially during the rainy season.
If you notice any areas where gravel has started to wash away, don’t simply add more gravel. It’s a sign you have a drainage problem on your hands. Improve current drainage or add more drainage options.
One of the most challenging aspects of maintaining a gravel driveway is clearing snow from it. Be careful not to scrape the gravel when plowing snow. Use salt to keep snow from building up too much.