Under Deck Drainage System: 12 Popular Options

The space below an elevated deck has many possibilities. It can be a living space that’s usable in wet weather or valuable storage space for gardening equipment, but only if the space is safe from the rain.

A good deck drainage system prevents rain from passing through the cracks in the above deck, keeping the space underneath dry. An under-deck drainage system includes above-joint systems that are installed as the deck is being built and under-joist systems that can be retrofitted to an existing deck.

Above joist systems not only prevent water from reaching the space beneath, but they also protect the deck framing from water, extending the life of the deck. Under joist systems create a finished ceiling, giving that underdeck space a more appealing look and feel.

In this article, we’ll examine both above- and below-joist options as well as other types of deck drainage systems, so you can determine which is the best for your deck.

How Do You Waterproof Under a Deck?

If you have an elevated deck with living space underneath it, installing a drainage system that prevents rainwater from seeping through the upper deck to the patio or deck underneath, while not essential, is an excellent way of improving the living space below.

A deck drainage system creates an outdoor living space that’s usable during inclement weather. It also allows for installing certain electrical elements, such as lighting or a ceiling fan, while also protecting patio furniture.

A deck drainage system can also allow you to create a storage space for yard equipment and other tools.

In certain situations, a deck drainage system can also solve drainage problems that may be causing water to pool underneath a deck or collect around the deck’s footings. Some systems will also protect the deck’s framing from water, adding years to a deck’s life.

It’s important to understand that many of these systems are not completely watertight. Many systems will still allow for drips or may not provide total protection during downpours.

What is an Under-Deck Drainage System?

True to its name, underdeck drainage systems are installed under the decking. Underdeck drainage systems catch and redirect water in one of three parts of the deck–on the deck’s surface, between the decking and the joists, or below the joists.

Some deck drainage systems installed into the cracks between the decking prevent the water from making it below the deck, causing the water to run off of the outer part of the deck or to a gutter that runs along the edge of the deck.

Below the Joist Deck Drainage Systems

Deck drainage systems installed below the decking consist of rigid metal or vinyl pieces that attach to the underside of the joists of the above deck. They are installed, so they create a slope that carries water to a gutter attached to the ridge of the deck beam, where it is directed to a drainage area.

A below-deck joint drainage system is ideal for retrofitting a deck as it doesn’t require the deck to be dismantled for installation. These systems attach to the underside of the joist.

Below the joist systems require more maintenance as debris that falls through the decking must be periodically cleared from the top of the drainage system. For this reason, most below the joist drainage systems have removable panels to allow the spaces between the joists to be sprayed out with a hose.

While this system creates an attractive ceiling for the living space under the deck, it doesn’t protect the deck’s framing from water. And, since the drainage system encloses the framing, it can take longer for the joists and beams to dry, which can cause problems.

1. DrySpace

DrySpace from Timbertech is an excellent option for retrofitting an existing deck. It works by fitting U-shaped brackets over the bottoms of the joists. Each bracket has a channel that holds a vinyl trough that spans the distance between each joist.

Each trough has a slope of 1/8 of an inch every foot, allowing it to shunt water that falls through the deck to a gutter that runs the length of the deck’s outer beam. That gutter system then sends the water to an area that grades away from the home’s foundation. This product works with joists that are spaced 12 to 16 inches apart on center.

Like many under joist products, In addition to providing a drainage system that keeps the area under the deck dry for other uses, it also creates an attractive ceiling that makes it ideal for underdeck living spaces.

It’s also made of vinyl, so it will more than likely outlast the life of the deck above it. This product comes in two neutral colors–bone and white and runs about $4 per square foot, making it one of the cheaper under-joist options.

2. Under Deck Oasis

Many underdeck drainage systems have large V-shaped channels that, while giving a finished look for space below, do not look like a normal flat ceiling. Under Deck Oasis is different.

This product features metal brackets that attach to joists, which in turn attach to metal panels. These panels drop about 1/8 of an inch per square foot from the ledge to the outer edge of the deck, sending the water away from the house. A gutter attached to the outer edge of the beam collects the water and sends it to a drainage area on the ground via a downspout.

What’s nice about this product are the panels, which resemble the paneled roof that many covered porches feature, adding instead of detracting from the space’s aesthetics. Visitors won’t even know there is a drainage system hidden in the ceiling.

This finished look makes this product ideal for elevated decks that cover a patio, lower deck, or other living space. Under Deck Oasis comes in various wood grain and solid colors with different finish types and runs about $6 to $9 a square foot.

3. Zip-UP UnderDeck

Zip-Up deck uses a series of vinyl rails that attach perpendicularly to the joists to create a slope that runs from the ledger board to the outer beam of the deck. Rails that attach parallel to the joists have a channel that holds vinyl panels that create the ceiling.

When water runs through the decking, it runs away from the ledger board, where it falls into a gutter that runs the length of the outer beam. This product uses vinyl material, which keeps it lightweight, so you won’t be adding any additional load to the deck. The materials are also durable enough to last the lifetime of the deck.

The finished product leaves a smooth ceiling without ridges, making it an attractive option for underdeck living spaces. The panels can be easily removed for periodic cleaning or to collect an object that has fallen through a crack in the decking.

This product is also one of the sturdier options, meeting certain hurricane standards. Zip-Up UnderDeck comes in three colors, including beige, grey, and white, and three finish options.

4. UnderShield

Certainteed’s Undershield system consists of 6-inch by 16-foot vinyl panels that attach to the underside of the joists via a bracket mourning system. These brackets consist of square-shaped lengths of vinyl that run perpendicular to the joists from end to end. The vinyl panels suspend from the ceiling via a bracket that attaches the panels to the mounting system.

This design makes it relatively easy to install this system to an existing deck. The brackets’ length is adjusted to create a 1/8-inch drop from the ledger board to the outer beam. When water drains through the deck above, it drops into the channels on the vinyl sheets and runs to a gutter system mounted on the outer beam.

This system features a finished ceiling look for space below, making it a good pick for underdeck living spaces. The panels come in two different styles–chamfer and beaded–and three color options: wicker, grey and white. UnderShield costs about $6 to $7 per square foot.

5. DuoDeck

DuoDeck uses brackets similar to deck hangers to hold a framing system for the deck drainage system. The galvanized metal hangers attach to the face of the joists. Long 2×2 that step down in height are then inserted into each hanger.

Corrugated PVC panels are then attached to the hangers using screws. The ripple shape of the panels functions as troughs, carrying away rainwater that falls through the gaps in the above decking. This method is simple to install and is a cheaper alternative to many of the more expensive options on this list.

If aesthetics isn’t’ a priority, that is an excellent budget option. It costs less than $3 a square foot and doesn’t require a pro for installation.

6. RainTight

RainTight offers one of the stronger and more durable products for underdeck drainage systems. Unlike other products, which feature prefab pieces, all of RainTight’s products are custom cut to the deck’s specifications. This means this isn’t a DIY solution; however, it also means that it’s exceptionally strong.

Whereas other solutions consist of vinyl, RainTight uses heavy-gauge aluminum. This not only means that it will last longer than plastic options, but it also means that it can hold more weight without sagging, which is crucial for places that see heavy rainfall or snowfall.

It also means the ceiling can support structures, such as lighting or a ceiling fan. RainTight works similarly to other underdeck products. Each panel rakes slightly toward the outer beam of the deck. Each features 1-inch deep channels that cause water to drain to a gutter mounted to the beam. DuoDeck’s RainTight product comes in five colors–bronze, sierra, linen, coastal dune, and white.

7. DRY-B-LO system

Dry-B-Lo offers one of the more time-honored deck drainage solutions, having been around since the early 1990s. The company uses what it calls Galvalume, which is a series of interlocking embossed metal panels that create a finished ceiling look while also channeling water away from the above deck to a gutter system that runs along the deck’s supporting beams.

Galvalume is 22 gauge, making it stronger than many other systems, so you don’t have to worry about the ceiling eventually sagging over time. The company also touts 3-inch high side walls with each panel, which is far greater than the 1-inch deep troughs that other systems use.

This means DRY-B-LO can better handle downpours that produce high volumes of water that can overwhelm other systems. This product uses a hidden channel system that attaches in between joists, which allows the finished ceiling to attach flush to the bottom of the joist without lowering the ceiling height. This allows for installing hardwood ceilings such as redwood cedar and pine and accessories such as ceiling fans.

8. DIY – Corrugated Fiberglass Roof Panels

Though not as aesthetically pleasing as many of the above options, fiberglass roof panels offer an inexpensive option with a simple design that makes it easy to install. This system works by attaching 2x4s or 2x6s that run perpendicular to the deck’s joists.

The lumber is attached using a succession of increasingly wide shims that create a slope of 1/8 inch for every foot away from the ledger board to the outer support beam. The corrugated sheets are attached to this framework.

The ridges of each sheet coupled with the slope built into the framing serve as troughs that channel water to the outward side of the deck. A gutter attached to the outward beam catches all of the runoff from the corrugated sheets and directs it to a downspout.

Although the roof panels may not be as attractive as other options, at about $1 per square foot, it’s significantly cheaper than other solutions.

Above-Joists Deck Drain Options

Drainage systems installed between the joists and the decking consists of a series of gutters made from either rubber polypropylene or some other waterproof material that drape between the joists.

When water falls between the cracks in the decking, it is captured by the system and funneled to the outer edge of a deck, where it drops into a gutter that then guides the water to a drainage area.

The clear advantage of the above-joist deck drain options is the added benefit of protecting all of the deck’s framework and providing a dry space for a living area or storage below the deck. By keeping the deck’s frame dry, these systems can extend the overall life of a deck by many years when properly installed.

The flip side is that they are difficult to retrofit to a deck, making them ideal for new deck construction. To retrofit an existing deck with an above-joist system, one needs to remove all of the decking then reinstall it once the drainage system installation is complete.

9. DEK Drain

DEK Drain consists of a rubber membrane that covers the entire deck frame. The rubber drapes over the joints to create wide troughs in each joist bay that are capable of handling a high volume of water.

Four-inch wide cap steps installed over each joist prevent water from reaching any of the deck’s framework. The troughs angle toward one side of the deck, where a gutter collects the water and guides it away.

This system is an excellent option because it’s custom. DEK Drain cuts all of the pieces to fit the exact dimension of the deck, creating a seamless covering with thick rubber that is virtually leakproof.

Since the product hangs between the joists as opposed to below them, you can install a finished ceiling for the living space or storage space below. DEK Drain is also a little more affordable than other options at $5 to $6 per square foot.

10 RainEscape

Trex RainEscape works similarly to DEK Drain. It features thick plastic sheeting that drapes between the joists to create large troughs in each joist that are sloped to guide rainwater to one side of the deck. Funnels at the end of each joist bay guide water into the gutters.

RainEscape is one of the easier products to install for homeowners. The troughs can be cut to size using a utility knife and attached with a staple gun. Caulk and flashing tape are used to waterproof seams and joints at the ledger board.

RainEscape is also one of the cheapest brand name-deck drainage products at about $5 a square foot. And, like other over-the-joist solutions, this product leaves clearance to install a finished ceiling flush to the bottom of the joists, concealing the entire drainage system except the gutters.

Other Options

11. Deck Flange Systems

One of the lesser-known advantages of composite decking is that many of these products are built for a simple yet effective deck drainage solution known as a flange system. Flange systems take advantage of the gap that runs the length of each composite decking board.

Deck flange systems come in long roles and consist of two plastic tabs that fit into that small troughs on two parallel deck boats. A third tab fills the gap between the deck boards. This creates a waterproof plug that essentially fills the gaps between the board, preventing water and anything else from passing through.

The water then drains off the edge of the deck, leaving the area underneath dry. This is perhaps one of the simplest solutions as it does not require draping plastic or installing a metal trough system.

It also conveniently prevents debris from passing through, eliminating the need to periodically clean out these aforementioned troughs. Of course, deck flange systems will only work with composite decking and must be installed when the deck is installed.

This product works with such brands as TimberTech, Fiberon, Deckorators, and Wolf and comes in 50-foot rolls and 200-foot rolls.

12. Combined Joist and Drainage systems

Realizing that many deck drainage systems incorporate the deck’s joists, Wahoo Decks created DryJoistz, which is a combined joist and drainage system. These joists are made from thick gauge aluminum, replacing the standard wooden joists in a deck, and can span a maximum of 6 feet, making them suitable for decks up to 24 feet deep.

Each joist includes a large flange that hooks to the adjoining joist, creating enclosed waterproof joist bays. When water runs through the cracks in the decking, the bays collect the water and carry them to the side of the deck, where it drains away from the deck.

Because it combines the joists with the drainage system, it’s only suitable for new deck installations. This system has the added benefit of a more durable deck frame, as aluminum will last longer than standard wood joists. This system works with both wood decking as well as composite decking.

How Much Do Deck Drainage Systems Cost?

Deck drainage systems can vary significantly in price. Corrugated panels are the cheapest option, costing about $1 a square foot, which equates to about $300 for the average size deck. Brand name systems are significantly more expensive, beginning at $4 a square foot and costing as much as $9 a square foot.

Under-joist systems that create a finished ceiling are generally more expensive than an above-joist system installed when a new deck is being built.

However, keep in mind that the above joist systems do not include the cost of a finished ceiling. Given that these systems use plastic and rubber, which isn’t particularly attractive, factor in the cost of installing a finished ceiling once the new deck and drainage system is installed.

Conclusion

A good deck drainage system can have a significant impact on a raised deck, creating living space underneath that is usable even in foul weather. It can also allow for valuable storage space for all that yard equipment that is cluttering up the garage.

Whether installing a drainage system on a new deck or retrofitting an existing deck, there are many options and various price points to consider when selecting a drainage system. Remember that few drainage systems offer complete waterproofing, which means ceiling fans or other electrical systems added to space below should adhere to outdoor ratings.