Synthetic Turf, Drainage & Flooding
January 31, 2023
Every year when monsoon season is upon us, we all know what that means… possible flooding. Over the last two years alone there has been record amounts of rainfall across the nation prior to monsoon season. What does this mean to the synthetic turf industry? …It means it could cost you and/or your customers thousands of dollars in damages. Just because your turf product drains 30+ inches per hour per square yard does not mean your subbase does.
“Does the turf you choose, and place have anything to do with drainage?
It sure does… it’s the first thing you should consider when choosing a product for each application. Synthetic turf has evolved over the last two decades and most synthetic turf products on the market today have drainage capabilities. Most turf products are hole punched to allow for proper drainage. Many Installers and clients primarily choose synthetic turf by its “appearance and feel”, ignoring the fact that the product they chose may cause long-term drainage issues. Turf manufacturers are understanding the importance for their products to allow certain amounts of water and fluids to drain through the backing.
Punching holes in the backing to allow for positive drainage has become the only way. The drainage holes vary with each manufacturer and each product. I have seen drainage holes from 2”, 3”, 4” and up to 8 inches on center. Bottom line is the more drainage holes the better drainage. The closer the holes are punched allows for contaminants to make their way through the backing and into the soil simulating natural grass. Synthetic turf products that have drainage holes farther apart from each other will create slow permeability rates. This means that excess water and fluids will not drain as fast and may cause flooding. Manufacturers are now creating synthetic turf that is 100% permeable. This means that the turf can take on a heavy rainfall … but will it take backseat to flooding?
You have heard me say often that if you “fail to plan, you plan to fail”. This can happen very fast after flooding occurs.
There is a misconception when it comes to understanding drainage in synthetic turf. Just because your turf product says it can drain 30+ inches per hour doesn’t mean your sub-base will. Understanding sub-base materials is very crucial to a successful installation.
Most turf installers think they can just cover up bad soils with good drainage soils. Eventually the underlying soils that are high in clay and/or conglomerates become fully absorbent, then reject water intrusion. This is when flooding occurs. If your sub-base is of poor quality, then I recommend over-excavating, remove, and replace with quality imported drainage materials.
If the area is known to have excessive flooding, then placing clean crushed aggregates to prevent erosion of the sub-grade and sub-base materials will be needed.
When choosing imported subbase materials for drainage and good permeability, I recommend aggregates that are created with high-quality hard rock, sand, and gravel. Below are types of materials that I recommend for placing underneath synthetic turf.
When placed in smaller lifts and compacted properly, these materials will retain density, allow permeability, and withstand excessive water penetration.
Crushed / Decomposed Granite
3/8” minus mixture
¾ washed limestone
“Getting the water to exit”
Many contractors and homeowners overlook potential flooding in their design. They overlook poor drainage thinking that placing synthetic turf will assist in the muddy backyard. Your yard may not become muddy anymore, but the water that created that mud must go somewhere. I have witnessed many installations where poor drainage caused extensive amounts of damage, flooding houses, buildings, restaurants, and sporting facilities all due to ignoring existing factors.
Below are some factors to look for when designing or installing synthetic turf on ALL projects.
. Does your synthetic turf drain? How much does it drain?
. Is the area located in a flooding area?
. Is the Installation in the path where large volumes of storm water will affect the design?
. Is the area higher than the buildings foundation level and/or stucco weep screed?
. Will you have to slope and/or re-grade areas to recreate positive drainage and exit of excessive flood water?
. Does the rooftop, balcony, and/or mezzanines have scoffer exits?
. Will you have to redesign, and connect underground piping from the scoffers?
. Have you calculated the size and square footage of rooftops, balconies and/or mezzanines that will dump rainwater upon your installation?
Storm/Rainwater must exit its initial surface and drain until it reaches its settling point. If the building’s rooftop is 10,000 square feet in surface area, then 1 inch of rain will produce approximately 8 thousand gallons of water flowing onto your turf.
Where will this added surface water travel?
. Does the existing area to be turf have drainage issues? And/or existing soils remain saturated?
. If a weed suppressor is to be installed, is it permeable? How fast does it drain?
. Does your installation require contouring? If so, will you create more issues by building mounds, preventing the escape of water?
There are many factors to think about on every new project that is to be completed. Knowing and being aware can prevent issues when it comes to drainage and flooding.
If the area you want to place synthetic turf in looks likes this? You will need to reconstruct the entire area to an elevation that will allow for the exit of water. Exit drains must be installed to prevent this type of flooding.
*** You will need to respect the sloping towards adjacent properties as well***
Exit drains, French Drains & Catch Basins
Excessive water run-off that floods synthetic turf areas will cause failure in the sub-base.
Exit drains, french drains, and Catch Basins should be considered when installing turf in areas where flooding may occur.
*** Make sure your backfilling of trenches around pipes and drains is firmly compacted***
Structures & Drainage
It is crucial to understand how structures that are outside your installations may aid flooding and damages. Rooftops, Balconies, and Mezzanines route flood waters to drains and scoffers that many times exit where your installations are being placed. I recommend speaking with the client and communicate possible drainage and flooding issues. If the elevations are not correct prior to your installation, they will need to be adjusted by either re-grading or placing exit drains. When doing your initial jobsite meeting it is a must to inspect the surroundings to ensure excessive flood water can be managed away from your installation. Before you go and start installing your turf, I recommend doing water tests to ensure the existing area has proper slope, drainage, and a place for the water to exit.
Rooftop, Balcony, Mezzanines and Scoffer Exits
Here is a beautiful installation by a successful turf contractor that relied upon the existing drains to do their job… but they didn’t. The drains failed because they were clogged to begin with. Once the rain started and flooding began, this storefront was overcome by waters that reached 6 inches higher than the weep screed and caused damage to the interior. The roof alone produced more water run-off than the installation had received. The scoffer exits added additional gallons of rainwater, contributed to the damage.
Prior to installing any turf in a backyard that’s rear elevation is higher than the foundation of the home or building, it is imperative that you do not take on the responsibility of flood waters. This putting green was placed in the center of the yard. The putting green had to be raised and leveled so that the golf ball wouldn’t roll off the surface.
Raising of the putting greens edge near the house caused the entire length of the putting green to be much higher than the threshold of the patio door. This caused flooding to the interior. The roof scoffers added to the problem by adding additional rainwater to flood the turf area. I recommend installing catch basins, drains and/or piping to allow for the escape of flood waters.
Foundation Level & Stucco Weep Screed
It is very important to keep the elevation of compacted materials below foundation weep screeds. Keeping all hardscape and landscape below the weep screed is required by most building codes and prevents water fromt entering the interior.
Creating positive slope and exit of hardscape flood water. When proposed turf areas are sloped towards areas of synthetic turf, I recommend installing exit drains to allow water run-off from the hardscape onto the turf and exit the yard successfully.
*** and again… Make sure your trenches around pipes and drains are firmly compacted***
Drainage pipe & Compaction
I have repeated the concern for compacting trenches when backfilling. This project definitely had poor compaction where drainage pipes were installed. This poor workmanship has now left depressions in the surface. These depressions no doubt will cause trip hazards and may cause injury. When placing drainage pipe, it is crucial that you compact the trench in lifts to prevent this from happening. I recommend a mixture of clean ¾ aggregate with the existing soils to prevent future settlement.
Respecting the “Weep Screed”
When installing synthetic turf between building foundations, it is imperative that you not only slope the area out and away from the building but keep the elevations below the “Weep Screed”. Weep Screed is a building material used along the base of an exterior stucco wall to prevent water from intruding the plate line and into the building. If you place your turf higher than the weep screed, it may cause water to penetrate the building’s interior. Make sure you maintain positive slope between buildings to ensure that excess water can escape.
Vegetation & Drainage
Over the years I have seen contractors ignore placing a weed barrier under the synthetic turf installation. The once beautiful installation they were so proud of turned into a nightmare several months later. The existing crab grass and broadleaf weeds grew up through the drainage holes of the synthetic turf and clogged it. Skipping this very important step can cause misery to both the client and the contractor and may cause flooding of the area due to the drainage holes being clogged.
“Does your weed barrier drain like your turf does”?
Placing a weed barrier below the synthetic turf after removing the natural grass is crucial. Using an inferior weed barrier that is not permeable and does not allow water to flow through quickly will cause flooding of the area. I recommend using a quality weed barrier that allows water and air to permeate 10 gallons per square foot.
Did you know that excessive flooding may cause growth of vegetation like mushrooms and weeds. Excessive moisture will allow all types of things to grow under the turf. It is best to try to keep your turf dry between cleanings and rainfall.
Turf Ribbons, Borders & Drainage
When placing turf ribbons and borders it is crucial to compact the subbase to perfection. Most turf ribbons and borders receive water run-off and If the base is not compacted to 80% or higher, the exiting water will saturate the compacted materials and cause settling which may cause injury due to be a trip hazard. I DO NOT recommend designing turf ribbons into your project unless you have positive slope to allow all fluids to exit the area quickly… If not? Your sub-base will settle.
Putting Greens, Traps & Drainage
A majority of putting green turf does not have drainage holes punched into the backing. This is to maintain integrity of the sub-base. The sub-base must maintain its hardness to prevent any changes to the putting greens surface. I recommend keeping all water away from putting greens. If you elevate your putting green to keep flood waters away, make sure the elevation does not hinder positive slope and drainage to the surrounding areas. Sand and grass traps must have an exit drain installed to remove flood waters from filling up and causing settlement.
Bocce & Lawn Bowling
Bocce Courts & Lawn Bowling have become very popular over the last decade. Flood waters can damage these surfaces to where replacement is the only option. If there is any settlement due to improper drainage it will cause irregular ball roll. Make sure you design the surrounding area to slope away from the courts.
Pet Turf & Drainage
In creating a successful pet turf area, it starts and ends with the fluidity of all substances penetrating through the surface of the turf. If the synthetic turf product does not have the ability to drain quickly, bacteria may form, and contaminants may remain between drainage holes and create lingering odors. As I mentioned before, make sure that the compacted base drains well and has good permeating qualities. If the soil in the area does not drain or permeate, you will have to remove and replace with a proper drainage material that will.
Contouring, Drainage & Flooding
“When should I go flat or when should I contour?” – This is a common question that I get asked all the time. When drainage is not a concern and you are free to be as creative as you’d like with your turf installation, contouring will set your work apart. When the subgrade materials are contoured by grading slopes and small mounds, the beauty of the synthetic turf comes alive allowing the fibers to open and close resulting in a natural looking surface. There will be many installations where you’ll have to decide whether to grade your subgrade flat or contoured. Some clients have preferences that you should accommodate since it is their project. There will be installations that proper drainage supersedes all requests for contouring or being flat. When you contour synthetic turf, you must understand that you are creating a slope where water runoff could possibly flood. If the exterior of the contour is up against a wall, curbing or building you must be careful not to create an area where runoff from the contouring will cause damage.
Drainage & Snowfall
In many states where there is record snow fall, I recommend placing a firm compacted base with quality “drainage rock”. When the sub-base is overly saturated excessive water run-off will occur. Make sure you have positive drainage away from the turf area.
Rooftops, Balconies & Mezzanines
Synthetic turf on Rooftops, balconies, and Mezzanines must have proper drainage. I strongly recommend placing a drainage grid below the balcony or rooftop application so water can run through the synthetic turf and drainage grid to allow water to escape. Without a drainage grid the longevity of the synthetic turf will be depleted due to thermal contraction and the buildup of contaminates.
To sum it all up. When existing soils below the turf are saturated with excessive rainwater, the compacted subbase will not receive anymore. When this happens the drainage holes become useless. When torrential rains hit hard, this action speeds up the waters escape, and may cause damage to surrounding areas. It is important for you and your team to learn all you can about elevations, slopes, drainage and flooding when it comes to installing synthetic turf.
And like I always say “There is never enough time to do the job right, but always enough time to do it over”
“Don’t be one of these guys” … JW Out