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If you're planning a new driveway or your existing drive doesn't shed water well, you may be wondering whether driveway drainage is important. Actually, it's very important. Done right, you'll barely notice it, but done wrong, and it can cause costly damage. So, what do you need to know about drainage for your driveway? We've done the research, and we have the answers for you!
Although installing appropriate drainage for your driveway is expensive, it will save you money in the long run. An improperly drained driveway can crack, buckle, or divert water into your home's foundation. To ensure good drainage, use one or more of these strategies:
- Install a permeable driveway surface
- Site your driveway for optimal drainage
- Grade the site to slope downward
- Install pipes, trenches, drains, and/or channels
- Utilize swales or dry wells to collect runoff.
Each of these strategies is best for specific situations. In the remainder of this article, we will describe each one and its average cost. We'll also discuss various options for driveway surfacing materials. Keep reading to learn more!
Why Is Driveway Drainage Important?
Driveway drainage is important for two reasons. First, good drainage protects your driveway. Water that seeps into the cracks in a driveway can freeze and expand, causing damage. Pooling causes discoloration, pocking, and algae growth. And water collecting along the sides of the driveway can erode the foundation beneath the surface material, causing buckling.
Second, driveway drainage reduces strain on city sewer systems. Heavy rainstorms often cause flash flooding in urban areas as rainwater runs off driveways and into the streets. To reduce this effect, many homeowners install permeable driveway surfaces that absorb rainwater to return it to the water table.
Permeable Vs. Non-Permeable Driveway Surfaces
In terms of drainage, there are two classes of driveway surfaces: permeable and non-permeable. Permeable driveways allow rainwater to penetrate through them and back into the ground. Non-permeable driveways, by contrast, shed water.
Permeable Driveway Surfaces
Permeable driveway surfaces reduce or eliminate runoff by absorbing rainwater and returning it to the soil. Over the past decade, engineers have developed a variety of permeable driveway surfaces.
Permeable Block Pavers
Permeable block pavers look like conventional driveway and garden pavers, but they let the water soak through. They come in a wide variety of sizes, shapes, and colors, making them ideal for any driveway. They are also DIY-friendly: homeowners can buy molds and materials and make the pavers themselves.
Homeowners have constructed driveways out of brick since the beginning of the auto age. Brick driveways provide a classic feel and fit well with older homes. Not only are the bricks porous, but also the gaps between them absorb rainwater and return it to the ground.
Flagstone And Slate
Like brick, flagstone and slate add a classy, high-end look to a home. While the gaps between bricks in a driveway are filled with sand, flagstone and slate are typically mortared together. However, the stones themselves are highly porous, so excess water easily filters through them.
Open-graded tarmac is a water-permeable variation on traditional tarmac. It is made with coarse gravel, leaving large air pockets that allow surface water to drain away. Open-graded tarmac looks identical to traditional tarmac.
Grass is an often-overlooked option for driveways. In urban areas where reducing runoff is critical, some homeowners choose alternating strips of concrete and grass, like those in the picture below. Another option is to lay grass paver grids and allow grass to grow through the grid's openings.
Are Gravel Driveways Permeable?
Gravel is another popular option for a permeable driveway. While they are relatively inexpensive to install, gravel driveways require extra maintenance to keep them looking good and functioning well: weeding, raking, and the occasional addition of new stones.
Gravel driveways are among the best options for permeability, as long as they are installed over a permeable base. The ideal base for a gravel driveway includes a bottom layer of baseball-sized rocks, a middle layer of gravel 2"to 3" in diameter, and a top layer of smaller, finish gravel mixed with sand.
Non-Permeable Driveway Surfaces
Concrete and asphalt are the two most common types of existing driveways. They have the advantages of being strong, durable, and low maintenance. However, they also have a major drawback: they shed rainwater rather than absorbing it. This can lead to problems if the driveway isn't well-drained, so careful design is critical for a non-permeable driveway. If your existing non-permeable driveway is not draining properly, consider investing in a good drainage system.
Concrete is the most common surface material for existing driveways. It is strong and durable, almost maintenance-free, and less expensive than decorative surfaces such as brick or flagstone. However, concrete driveways can crack and pit if not drained effectively. In cold climates, water can infiltrate small gaps or cracks and then freeze and expand, forcing the cracks to widen. In addition, pools of standing water on concrete can cause discoloration, pitting, and algae growth, which can harm the driveway.
Nonporous Tarmac (Asphalt)
Asphalt also remains common as a finishing material, especially for rural and suburban homes' long driveways. Nonporous tarmac is made from sand or finely ground gravel mixed with tar. Because the aggregate is so small, there are no air pockets for rainwater to filter through. Standing water can damage a tarmac driveway with cracks, potholes, and erosion of the driveway's foundation.
How Do You Drain Water From A Driveway?
Several factors determine how well a driveway drains. The type of surface material is, as described above, a key factor. But there are other ways you can ensure great drainage for your driveway, as well. If you are building a new driveway, you can plan for success from the beginning. And if you have an existing driveway that isn't draining well, there are still several options that can help.
If you're planning a new driveway, location is the key. Make sure you site it in a high and dry location, avoiding dips and hollows where rainwater might pool. If possible, avoid installing your driveway on wet or sandy soil because these may not adequately support the driveway's foundation. Of course, the layout of your land and the texture of the soil aren't things you can easily change, so you may also need to employ some of the other strategies described here.
The term gradient describes the slope of your driveway, from side to side and end to end. If you're building a new driveway, carefully planning the gradient can make a world of difference in its drainage. This is especially true if you're using a non-permeable surface like asphalt or concrete: the right gradient will allow the driveway to shed rainwater quickly and efficiently. The following are general guidelines for driveway gradients:
- Side to side: the center crown of your driveway should be 3" to 4" higher than the sides. Also, make sure that the driveway edges are higher than the ground that borders them so runoff doesn't pool alongside the drive.
- End to end: in most locations, a 2% grade is ideal -- meaning, from the top of the driveway down to the street, your drive should slope downward about 2 feet for every 100 feet of driveway. This gradient allows the drive to shed rainwater into the storm drain or culvert at the street. Depending on the locality, codes may allow a gradient as low as 1% or as high as 2.5% .
Pipes, Trenches, Channels, And Drains
There are several ways you can improve the drainage in an existing driveway, as well. A variety of pipes, trenches, channels, and drains are available at home improvement stores. Each of these options involves digging or cutting a hole at a strategic location in your driveway's surface and then installing the product. Water drains into it and is directed outward to the sides of the drive. These options are easily incorporated into new driveways, as well, to help with drainage.
Swales are deep ditches on either side of a driveway intended to catch runoff. They are typically used in rural areas where their steep sides will not pose a safety hazard to pedestrians. Installing a swale is usually a last resort in areas where intense rainfall and lack of ground cover can result in flash flooding.
In rural areas without public sewers, dry wells may be used to capture storm runoff and slowly release it into the ground. Dry well systems are readily available online and at many home improvement stores. They work in combination with drains or pipes that channel water away from the driveway and into the dry well's reservoir. Small holes in the reservoir allow the captured water to slowly drain into the surrounding soil.
How Much Does It Cost To Install A Driveway Drain?
Unless you are a highly experienced DIYer with a strong grasp of all the facets involved in driveway drainage, you should probably hire an expert to plan and install your driveway drainage system. While this will not be cheap, doing it right the first time will save you money and headaches over the long haul. The following are average costs, including installation and materials, for the most common types of drainage:
- French drain: $1,000 per 100 linear feet
- Trench/channel: $4,000 per 100 linear feet
- Culvert/swale: $4,000 per unit
- Dry well: $2,000 per unit
While driveway drainage may not be the most exciting part of owning a home, it is essential. Making sure that your driveway sheds or absorbs rainwater properly will keep it in good condition and prevent costly repairs down the line.
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