Trench Drains and Slotted Drains for Swimming Pools & Splash Pads

We should break pools out into two different categories – indoor and outdoor swimming pools.

Indoor swimming pools are generally more accepting of different materials because you don’t have problems with ultraviolet light, debris, and generally have a temperature controlled environment.  Interior pools only need to capture water that is splashed out of the pool or dripping off of swimmers.  A 2″ or larger trench drain will effectively do the job.  Drains with removable tops are always recommended to make long term maintenance easier.  Even indoor applications will see enough sand and sediment to plug a small profile drain over time.  For commercial applications it is still recommended that a larger 4″ I.D. drain be used.  Slotted drains with clean-out ports should also be considered especially for applications using tile and stone for a sleek look.

Outdoor pools should be 4″ I.D. minimum.  The debris will plug any system smaller than this in a very short time.  Choose 4″ outlet piping or larger so that the system will pass any debris that gets into the trench drain.  Any outdoor trench drain should have a removable top for cleaning of debris or clean out ports for slotted drains.  Outdoor trench drains should also be UV resistant.  Be careful of colors and materials that can heat up and potentially burn bare feet.  The sun can make many dark colored or metal drain tops too hot to walk on.

Eric’sons Dura Trench recommends that linear drain products should be installed at a distance of 3 feet and 1 inch minimum from the inside wall of all pools. However, if the design necessitates a linear drain product to be within the 3-foot perimeter of the inside wall of the pool, it is necessary to specify proper bonding (grounding) of the linear drain metallic components in accordance with NEC 680.26.

Drain tops should be slip resistant and toe proof.  Look for grates that have small openings that kid’s toes will not get into.  Grates with a nonskid surface are preferred.

Design Considerations

Sizing the drain

• For indoor applications size is not generally critical.  The water volume is small, only catching overflow from the pool, dripping water from swimmers, or wash down water from a garden hose.
• For outdoor applications a 4″ drain is preferred as more water will be present from rain events and debris loading will be greater.
•  Stay away from drains less than 4″ wide for outdoor applications because they will get clogged and require frequent maintenance.
• Be aware that commercial pools have significantly more swimmers and therefore will potentially have more water flowing through them.  A 4″ pre-sloped drain is recommended for large pools where there will be a lot of swimmers at one time.

Choosing the channel

• Choose channels that are resistant to common pool chemicals.  Some of the common chemicals include sodium hydrogen sulfate, sodium carbonate, hydrogen peroxide, calcium hypoclorite, hypocloric acid, and potassium peroxydisulphate.  These chemicals are typically dilute, but over long periods of time can corrode many materials.  Don’t use steel or iron products in close proximity to the pool edge.
• If this is an exterior application also ensure that the drain will not degrade with exposure to ultraviolet light (UV light).
• The channels should receive only foot traffic in these applications so the channel will not need a heavy duty frame.  The biggest concern with the channel edge is that it must be smooth and not have any sharp edges.  Swimmers will have bare feet that are easily cut on anything sharp.
• Sealing channel joints is a good idea but not necessary in this application.
• Both interior and exterior pools that will not be temperature controlled often have long trench runs.  These trenches will see severe changes in temperature.  In some cases this can cause a trench to prematurely fails.  It is best if the trenches have similar thermal coefficients of expansion to that of the surrounding concrete encasement.  For more information see material properties.

Selecting the grate

• Grates for pools range in price from very inexpensive to extremely expensive.  Plastic grates are quite popular because they are very inexpensive and tend to hold up well in this environment.  The down side to a plastic grate is that they can be very slick when wet and are not as heavy duty as other materials.  If you choose a plastic grate be sure that they are UV inhibited and look for grates with some traction features on top of the grate.  The next choice up the cost ladder is cast iron or ductile iron.  These will last a good while next to a pool but they will rapidly corrode.  They also have the potential to stain a porous deck surface.  Stainless steel is a good choice for chemical resistance and longevity.  The down side to stainless is cost, they can get slick when wet, there is a possibility of sharp edges, and the metal can heat up and be hot on bare feet.  Stainless grates are nice looking and work great especially when the width is kept to a minimum.  Another option is a fiberglass grate with grit impregnated into the surface.  They do not get hot, are skid resistant, offer UV protection, and do not corrode.  A fiberglass grate will usually cost you about half the price of a stainless steel grate but more than a plastic grate.  They are incredibly strong and will last a long time in this type of application.  Fiberglass is a better choice than plastic if there will be any heavier traffic.
• Make sure that the openings on the grate are small enough that children’s toes will not get caught in the grates and cause injury.  The smaller the openings the more frequent cleaning of the grates will be necessary.
• Watch for sharp edges.  Any sharp edge, whether on plastic or metal, can potentially cut a bare foot.
• Look for slip resistant finishes.  Slipping on a trench drain can cause serious injuries.  This is a good reason to stick with smaller width trench drains around a pool.
• Be selective when choosing the method of locking down the grates as the locking mechanisms need to be comprised of a material that can also handle the pool chemicals.  Stainless steel hardware is typically used.

Designing the layout

• The trench drains are typically no more than 10′ to 12′ from the edge of the pool.  Place the drain around the entire pool to catch the chemical laden pool water.  You do not want this water to damage landscaping or make pedestrian areas slick.  This also catches any water that might have debris in it before it reaches the pool keeping the pool cleaner.
• If you are considering a stainless trench drain system check the codes to see how far away from the pool you need to place the drain to avoid grounding issues.  Metals near water often have to be grounded by code if they are within about 5 feet of the pool.
• Be aware of the depth of the system that you are going to use to avoid conflicts with piping and other buried utilities.
• Outlets should be placed to minimize piping, but beware that many pool systems are non-sloping trench bodies.  If you select a non-sloping trench body outlets need to be spaced at 20-30′ in order to move high volumes of water that may be present in commercial pools.  Using a sloping trench system may be more expensive, but the higher cost may be offset by the reduced piping and maintenance of the system.
• To get the drain around the entire pool you will need to turn some corners.  If possible make the corners the high points as flow is restricted through the corners.  In many applications this is not possible and the flow must go through the turns.  Design the layout to minimize turns if possible.  Where turns are necessary make sure that the cuts are smooth, the inverts should line up, and the joint should be sealed with a quality rigid two part epoxy.  When possible get factory fabricated turns.