The slope or grade of a driveway determines how drivable it is, especially when it snows. It also affects drainage both on and off the driveway.
Experts generally recommend a max 12-15% driveway slope. Any steeper than that and you’ll have trouble driving or walking up the driveway.
Below is a quick guide on driveway grading with tips on how to slope your driveway.
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What’s The Best Slope For A Driveway?
The slope of a driveway will greatly depend on the slope of the area you plan to build it on. Hilly neighborhoods usually have to make do with steep driveways.
But you still have some flexibility on how steep the driveway will be. For instance, you can design a gently sloping driveway on a very steep area or add more slope to a driveway that’s built on a flat area.
Driveway contractors generally recommend a maximum driveway slope of 12%. This means the driveway rises by a maximum of 12 feet over a distance of 100 feet.
But you can usually go up to 15% without major problems.
That’s not to mean that you can’t build a driveway steeper than this. Most cars can navigate up driveways as steep as 25%.
But having a driveway that’s too steep (more than 15%) can cause several problems:
- The bottom of your car could scrape the driveway.
- Your vehicle could slide down the driveway and onto the streets in icy conditions.
- Delivery trucks will have trouble going up the driveway.
- Emergency service vehicles such as ambulances and fire trucks could also face difficulty reaching your home.
- If the driveway is made with an impervious material like concrete or asphalt, it could create heavy runoff onto the street or your home depending on which way the driveway slopes. This can lead to all sorts of drainage problems, and could lead to flooding in your yard or garage.
- You might be in violation of your city’s building code. Before you build the driveway, check if the city or HOA has any rules regarding driveway slope.
So if you can, keep the driveway at 12% slope or less.
But don’t make it completely flat either. Sure, a flat driveway is easy to drive on, but it’ll have drainage issues.
Experts recommend a minimum grade of 1-2% for driveways and other outdoor paved surfaces. That means the driveway should rise or drop 1-2 feet over 100 feet.
What Is A Good Cross Slope For A Driveway?
The slope from one end of the driveway to the other is not the only one that matters. The side to side slope is important, too. This is called the cross slope. It’s important for driveway drainage.
A driveway can have three kinds of cross slopes depending on whether it’s straight or curved.
For straight driveways, a crown design is recommended. This is where the driveway is higher at the center and slopes to the sides, allowing water to quickly drain off the driveway.
If the driveway is curved, you can design the entire surface of the driveway to slope towards just one side. It can either be in-sloped (drains upslope in a ditch) or out-sloped (drains downslope).
Whether you have a crown, in-sloped or out-sloped driveway, experts recommend a cross slope of about 2%. This keeps the driveway almost flat, with just enough slope to ensure water doesn’t pool on the surface.
If you have a gravel or an unpaved dirt driveway, a steeper cross slope of 4-6% is recommended.
How To Measure and Calculate Driveway Grade
Measuring the grade of a driveway is easy, and you can do it on your own. You should know the grade of your driveway before you start any work building it.
That’s because you need to maintain this slope when excavating the ground, adding the base materials and laying or pouring the driveway.
If you are resurfacing or re-doing an old driveway, you also need to measure the current slope and decide if you need to adjust it.
The slope or grade of a driveway refers to how much it falls or rises for a given distance. So that’s what you need to measure.
The easiest way to do this is using a long string. Have someone hold one end of a string on the ground where the top of the driveway will be (typically where it meets the garage).
Then hold the other end of the string at the bottom of the driveway, making sure the string stays level (use a spirit level to check). Measure the height of the string from the ground in feet. You can tie the string to a stake to make it easier to measure its height.
Divide this number by the length of the driveway or string, then multiply by 100 to get the grade as a percentage.
So if you have a 100 foot long driveway and the height of the string at the bottom of the driveway is 5 feet, the driveway slope is 5% (5/100 * 100).
Of course, you can also measure these distances in inches. But don’t mix feet and inches. Use one or the other.
When building the driveway, you can adjust its grade to improve drainage or drivability. Use a string and stakes to mark the slope of the driveway.
Say you want an 8% grade on a 250 feet long driveway. The driveway must rise 8 feet for every 100 feet, or 20 feet for the entire 250 feet length of the driveway.
Tie a string at surface level at the top of the driveway and at a 20 feet height at the bottom of the driveway. This will guide you when pouring or paving the driveway.
Here’s a great video on how to measure slope.
Note: This method only applies to straight driveways. If you have a curved driveway or your driveway has switchbacks, you’ll need to measure individual straight sections.
Should A Driveway Slope Towards or Away From The House?
If possible, the driveway should always slope away from the house. This directs water runoff away from your home and the foundation.
If you have the driveway sloping towards the house, you risk water flooding into the garage. The area around your home can also get too wet, affecting the integrity of the foundation.
If it’s not possible to have the driveway sloping away from the house, maybe because your house is lower than the street, then you’ll need adequate drainage to carry away stormwater.
How To Make A Driveway Less Steep
It’s not always possible to have a 12% or less driveway slope. If you live in a very hilly area, you might have to build a steep driveway.
But there are a few ways you can reduce the slope of a driveway.
- Make it curved – instead of going straight up, make the driveway curved. This reduces the grade of the driveway and makes it safer to drive on.
- Add several switchbacks – for long driveways, switchbacks are great for reducing the slope of a driveway. The driveway zigzags across the slope instead of going straight up. But this requires plenty of space. It also costs more since switchbacks make the driveway longer.
- Build the driveway to be higher or lower than the surrounding land. This lets you build a less steep driveway, though it’s expensive since it requires excavating deeper into the earth or using lots of material to raise the driveway. You may also need to build retaining walls.
I highly recommend talking to a pro such as a civil engineer. They’ll advise you on the best driveway design depending on the slope of the land.
How To Fix A Steep Driveway?
If you already have a steep driveway and don’t have the budget to replace it, there are a few things you can do to make it safer and easier to use.
- If you struggle to drive up the driveway especially when it snows, pouring gravel on the driveway can help increase traction. This gravel will slowly wash off, so be ready to add a new layer every now and then.
- If replacing the driveway is beyond your budget, consider resurfacing it instead. This works for concrete and asphalt driveways. Resurfacing involves adding a new layer of material at the top. When done right, resurfacing can reduce the slope of a driveway.
- Add a transition ramp at the bottom of the driveway to keep the bottom of your car from scratching the ground when entering the driveway. You can build a permanent ramp or install a ready-made rubber curb ramp.
- If you are experiencing drainage issues, build a channel drain across the driveway to collect runoff. A French drain or swale can also help reduce runoff and flooding.
If the driveway is too steep, you may have no option but to re-grade it. It’s not as expensive as building a new driveway since you don’t need to lay a new base.
Just remove the driveway surface and add a layer of gravel or sand to adjust the slope of the driveway. Then lay a new driveway on top. If you have a paver driveway that’s not too old, see if you can reuse the pavers.
If it’s a gravel driveway, you can also return the same gravel that was there.
2 thoughts on “What Is A Good Slope For A Driveway?”
The slope leading up to my house slopes slightly TOWARDS the house. Is it possible to change this before I install a driveway so that the water would drain away?
Absolutely! You will have to look into your local planning laws, and ensure that you still install some sort of drainage (gravity won’t do it all for you), but you can change the slope to a more convenient, away from the house slope before you lay your driveway.