Grading and Drainage Problems & How to Avoid Them (Updated 2018)
Grading and drainage problems around your yard and home can be a serious problem. Not only does poor yard drainage wreck your landscaping, but it also significantly increases your chance of developing adverse structural movement.
If you live in the Gulf Coast Region, this is a legitimate possibility due to our poor soil conditions.
Seasoned home inspectors will evaluate thousands of residential grading and drainage plans. A percentage of the home’s evaluated will suffer severe damage from grading and drainage problems. What’s worse, a high percentage of the damaged homes only needed moderate corrective action to avoid being damaged.
Five Negative Effects of Grading and Drainage Problems
- Ponding water around the home’s foundation over-saturates the expansive soils. Expansive soils are often compared to a sponge, in that; adding volumes of water causes them to expand. The outward pressure from the soil expansion can seriously disrupt your supporting soils. The cause of structural failure can be linked to grading and drainage problems for a large percentage of homes.
- Poor grading and drainage directly against the home or garage can allow water to damage lower trim boards and siding. Worse still, rising water can enter the structure or be pulled into the wood framing members via capillary action (wicking).
- Ponding water around your lot is a bastion for mosquitos. Nobody wants this.
- Ponding water and stagnated soils kill your grass. If you have a dog(s); it’s going to be mud city.
- Your landscaping will significantly suffer, and nobody wants to get their clean shoes dirty
Now that we know the risks associated with poor grading and drainage we need to understand the basic concepts involved in the problem.
- Explain the most common grading & drainage plan implemented in residential-construction
- Discuss the advantages and disadvantages
- Discuss the most common supplemental drainage systems
Basic Residential Grading & Drainage Designs
The most commonly constructed grading and drainage design in residential areas is a drainage swale. In general, each home in a subdivision is constructed so that it is self-supporting.
Your lot boundaries should collect the rainwater and roof run-off and direct it towards an approved collection point.
The most common approved collection points are road ditches, streets, and retention ponds. Ideally, this is achieved solely through surface drainage.
Drainage Swales in Residential Development
Each lot in a subdivision has its own drainage swale. The rear of the lot will have a higher elevation that slopes towards the back of the home.
At a midway point between the swale and the home, the grade is re-directed towards each side of the home; where it will continue sloping down-hill until it reaches the approved collection point.
Five Drainage Swale Advantages
- There are no extra material costs and can be constructed in a day (or less)
- Limited or negligible harm from erosion over time
- The simple design allows for manageable homeowner upkeep and improvements
- Deters water collection and run-off from adjacent lots
- Can control the rate at which surface drainage flows, preventing erosion and stagnation around the lot
Five Drainage Swale Disadvantages
- The side swales are often joined with the neighboring lot, creating a single shallow trench (Texans = ditch). If you or your neighbor’s lot is not properly draining; you’ll both suffer.
- Fences are often constructed down the center or in the path of the side swales, which often causes the surface water to stagnate and pond.
- It can be difficult to slope rear patios into the mid-way point of the rear swale, often causing ponding directly against the rear of the home.
- Some drainage swales have to be constructed with abnormally steep slopes to function; limiting the use of the yard for certain activities.
- If the production time is quick throughout the development, the lot has a high chance of holding water; requiring the use of catch-basins and other supplementary drainage solutions; increasing upkeep and maintenance costs.
How to Improve Grading and Drainage Problems
We’ve discussed the structural implications associated with grading and drainage problems, as well as some of the other concerns. If you’ve made it this far, I have to assume that your yard is holding water and you want to know what is commonly done to improve your drainage.
The most common supplemental drainage system installed to improve a drainage swale is an underground catch basin system.
I don’t want to discuss the installation of a catch-basin system in this article (I’ll write a more in-depth article for that soon), so I’m going to keep the explanation very simple (NDS made an excellent video in 2012 that explains the project).
- Locate the plastic “basin” in the center of your ponding water. The basin should be set just below the grade for water to drain into it
- Dig a trench with a down-hill slope away from the home and in the direction of the water collection/discharge point
- Connect the 4-inch flex-drain to the catch-basin and place in the trench. You may need multiple catch-basins to solve your grading and drainage problems
- Back-fill the trench and monitor over time. If the ponding continues you’ll need to make adjustments to the system, possibly adding additional basins
Product Links: I linked to an NDS catch-basin that can be found at most local hardware stores or on Amazon. I prefer the way the lower sump area and grate system functions on the NDS catch-basins, but other brands are about the same.
The 4-inch flex drain connects to the catch-basin and will be what carries the water away from the home. Make sure to buy the solid flexible 4-inch pipe for this; we don’t want the perforated drain pipe. Also, 25 feet is the most common length needed, but you’ll want to estimate your own drainage requirements and purchase accordingly.
Gutters & Downspouts
The primary purpose of a guttering system is to collect roof drainage and discharge it away from the base of the structure.
Some lots have excellent surface drainage and wouldn’t benefit from gutters.
But, if you and your neighbor have less than 5-10 feet between the roof drip line and the fence; you will benefit from adding gutters.
I know you probably don’t want to spend money on gutters, but it may be the sub-system that your yard needs to drain properly!
If your grading and drainage problems are located on the sides wales; gutters will definitely help improve the problem by collecting the roof drainage and discharging it towards the front of the home.
Further, gutters prevent impaction and erosion that happens when water falls from the roof. The drip line created by the lack of gutters disrupts the surface drainage, adding to the problem.
Bonus Tip: Purchase the flex-drain downspout extension and insert over the end of your gutter downspout to help discharge water away from the foundation. In my experience, this method of discharge is far superior to having a splash block placed below the downspout.
Common Types of Grading and Drainage Problems
Rear Swale Holding Water
The rear swale is prone to holding water if the lot was improperly graded. If you notice any stagnation or heavily saturated soils more than 48 hours after the last moderate to heavy rainfall, you likely have a drainage issue.
Sometimes a little shovel work can solve your issue, but that may only re-locate your problem to another section of the yard.
Installing a catch-basin and underground drain is probably a better option.
Side Swale Holding Water
The majority of surface drainage problems that I encounter are on the side swales.
Limited room between the house and fence, lack of gutters, HVAC pad and storage buildings all impede the flow of surface water, which results in ponding water too close to the foundation.
A bit of shovel work is often the only repair needed to improve the condition.
Water Ponding at the Rear Patio
If you have water collecting against your rear patio or flatwork, it is essential that you make timely repairs.
It is likely that the back patio is only 3-4 inches thick, which makes it more susceptible to heaving, which leads to cracking.
Also, negative drainage at the rear of the home can cause water to back-drain onto the flatwork, causing water staining and is a nuisance.
Grade Levels Too High Against the Side of the Home
It is crucial that we keep the exterior grade at least 2 inches below the exterior cladding.
When the soil or landscaping is stacked too high against the home, water will infiltrate the lower wall section, causing damage to the structure.
Also, high soil conditions can allow wood destroying insects like termites and carpenter ants unseen access into the home.
Grade Levels High and Sloping Towards the Home
Having high soil against your home is bad enough, but worse still is having high soils with negative drainage.
Directing water at the structure is a bad idea for many reasons, the most obvious of which is direct water flow into the structure.
If your home has a similar problem, it is critical that you make timely repairs.
Gutters Missing Downspouts
Most homeowners are aware of typical gutter maintenance like cleaning out debris and securing and sloping the downspouts, but some gutter installers forget to provide the downspout.
High volumes of water draining onto the side of the home is an excellent way to cause damage to your structure.
Well, there you have it. I hope that you learned something about your grading and drainage problems.
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