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Here’s Why Your Parking Lot Drainage is So Important

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Parking Lot with Standing Water

Water is one of nature’s greatest wonders. It sustains humans, and all other life on this planet. Without water, life would altogether cease to exist. However, that doesn’t mean water isn’t an enormous pain in the butt when it gets into places that it shouldn’t. Everyone has experienced the mighty power water wields. Waves, freezing rain, flooding, hail storms; we could go on and on. Though often water does damage on a much smaller scale. If you’ve ever had water seep into your asphalt or concrete, you know exactly what we’re talking about. It’s a problem that most property owners overlook. Surely water will simply drain off my lot and into the ground, right? Well, sort of. That’s what supposed to happen, but that doesn’t mean it’s what’s going to happen. Standing water in your parking lot will cause real issues. We’re breaking down the whys and hows to parking lot drainage, so you can avoid water damage.

Potential Damage

Water damage to parking lots takes various forms. The varying conditions that parking lots deal with makes them particularly susceptible to damage. We’re going to break down parking lot damage by category, so you’re prepared for any scenario.

Water Damage Before Pouring Asphalt

Believe it or not, your parking lot is set up for potential damage long before anyone pours the initial asphalt. Water runs from high elevation to low elevation, and this is no different just because you’re planning a parking lot. Low elevation ground that’s subjected to years and years of water flow will have unstable soil. It’s nothing you can change, rather something you’ll need to keep an eye out for. Soil in natural drainage lines is structurally compromised far deeper into the Earth than you’ll dig for your parking lot.

Asphalt Damage After Pouring

Water that pools on your parking lot surface has the potential to wreak havoc on your asphalt. This form of water damage is especially bad for two reasons. First, it destroys the very bonds that hold your asphalt together. Once water settles onto your asphalt (the end result of poor parking lot drainage), it begins to separate the asphalt mixture from its aggregates. Second, water that settles on your parking lot surface causes damage very slowly. You probably won’t see the damage happening, which makes it hard to know just how much aggregate separation has actually occurred.

Other problems from pooling water include:

  • Bleeding: When the asphalt binder rises to the surface (part of aggregate separation)
  • Cracking: Water pressure causing cracks in your asphalt surface.
  • Raveling: Disintegration of the top-most asphalt layer.
  • Rutting: Depressions in areas of high traffic (wheel-shaped ruts).

Again, this damage is silent and only becomes apparent after it’s too late. Make sure you’re monitoring your parking lot surface on a daily basis for any standing water.

Structural Damage

Structural damage is possibly the worst kind of damage that inadequate parking lot drainage can cause. How it happens depends on your particular drainage problem. Though, the common culprits are easy to identify. Water that’s pooling onto your asphalt isn’t just damaging your surface coating. Oh no, that water is seeping into the very pores of your parking lot. It makes its way through your parking surface and into the subgrade, causing unseen structural issues. Let us emphasize, unseen structural issues are among the worst you’ll face. You won’t know they’re coming, and they will very likely cause property damage. For instance, imagine you’re dealing with compromised subgrade from improper drainage. You won’t know this until the asphalt gives way and collapses under the weight of a vehicle. This phenomenon is what is commonly referred to as a sink hole. Now, that’s an extreme example, but it’s always best to understand the worst case scenario. Typical subgrade damage results in pot holes and low spots forming across your parking lot. The low spots are particularly troublesome, because they compound the water pooling issue, and aren’t correctable without removing a large chunk of your lot. Subgrade structural damage is also possible when water collects at the edge of your parking lot. Saturated ground around the edges of your asphalt can allow water to seep under the entire lot. This commonly happens when someone builds their parking lot on ground that’s located at a natural low point.

Collateral Damage

The rest of the danger water poses to your lot isn’t from structural or surface damage, but rather causes liability. Parking lots that pool water or have pot holes are hazardous to people walking, and sometimes even driving. People can get hurt walking across the slick surface, much like cars can hydroplane from standing water. Your lack of parking lot drainage could potentially hurt a pedestrian and cost money in legal fees. Not to mention the bad publicity that could result from the headlines, “Pedestrian Suing ‘YourCompanyHere’.” Oh, and then there’s always negative Yelp reviews about your parking situation. The lost revenue will probably cost you more than just maintaining your parking lot.

Parking Lot Drainage Solutions

Parking lot drainage has much to do with your specific situation. Like the various kinds of damage, there are various solutions to staying water free. We’ll start with the basics and work our way forward.

Draining The Subgrade

That water damage before pouring asphalt? Well, with a little ingenuity (and reasonable amounts of water) you can still pour your parking lot. Drainage systems are available to install underneath your subgrade. Water then runs into the subgrade is simply drained to a lower gradient. This keeps your structure sound without having to account for excess water. In fact, always installing under-drains isn’t a bad in areas with very high rainfall. It’s much easier preventing structural damage than fixing it. It’s also wise to have your asphalt poured extra thick in areas where rainfall and groundwater levels are high. The ticker slab of asphalt can help resist cracking and aggregate separation. Water will interact with your surface, but you can do your best to mitigate the damage.

Testing The Subgrade

After you’ve had any drainage systems installed, it’s very important that the contractor still tests the subgrade for structural integrity. This means conforming to the standard uniform density of 95 percent, necessary gradients, and load-supporting characteristics. Essentially, you need to know that your drains are working, and that the deeper lying soil isn’t going to collapse after several years of bearing weight. Some weakness is ok, so long as the contractor removes the offending subgrade material, and replaces it with stronger crushed stone or concrete.

Slope, Grade, and Gutters

The best way to keep water off your parking lot surface is to slope your asphalt pour. This means creating artificially high and low points on your surface. We implement these slopes so that rain water won’t pool on your lot. Ever notice how roads slope towards the culvert? Same thing here. Efficient parking lot drainage slopes need to achieve a grade (measure of the physical slope) of 0.4 percent. Grades flatter than 0.4 percent are prone to puddling, and all of the aforementioned consequences that come with standing water. Flatter grades can work, however, with the implementation of storm sewers. Storm sewers allow run off water to flow into large grates. If you’re having a hard time visualizing, think of any large city after it rains. All of that water you see running is headed into the storm sewer. Parking lots with steep enough grades are candidates for curb gutters, which funnel water into either a nearby storm drain, or other low elevation ground. The curb gutters rely on gravity to move water, meaning it’ll take a combination of proper gradient and subgrade planning to make them work well.

In Summary…

Improper parking lot drainage systems could cause real damage to your parking lot. Both your asphalt and the underlying subgrade are in jeopardy. If you haven’t poured your parking lot yet, you’re in luck. This guide can give you all the inside tips and questions you should ask your contractor along the way. It’s especially important to make sure that your subgrade is sloped, drained, and up to code. As we mentioned earlier, it’s much easier to do something right the first time than trying to fix to later. Unfortunately, if your parking lot is already poured, you’re left with fewer options. However, that doesn’t mean you have no options for parking lot drainage. It’s possible to install curb gutters and storm sewers after pouring your asphalt, though more difficult and expensive. Current parking lot owners are better off monitoring their existing parking lot drainage systems for flaws. If you have no drainage systems at all, well, take note of where that water pools. Chances are that’ll indicate where damage will occur. If you’re a business owner looking for an easier solution to property maintenance, look no further. Our team has years of experience in the industry, including experience with asphalt and storm sewers. We’re proud to manage retail properties, commercial properties, HOAs, and industrial sites. If that sounds like your business, we’re happy to help.

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