What the choice really comes down to
Almost every under deck drainage system on the market is trying to solve the same problem: rain falls through the gaps in a standard deck surface, lands on the joists and beams, and slowly rots the structure from the inside. Where the systems differ is where they actually stop that water. Some stop it at the walking surface, before it ever touches a joist. Others let the water fall through the deck as usual and catch it later, underneath the framing, with a tray or membrane. That single distinction, surface versus underneath, is the one thing you need to understand before you compare anything else: price, warranty, install time, or finished look.
It matters because the framing of your deck is a structural investment, not just a cosmetic one. A system that keeps the joists dry protects the thing holding your deck up. A system that only protects the space and furniture below the deck is solving a comfort problem while leaving the structural problem in place. Neither goal is wrong, but they are different goals, and you should know which one you are actually buying before you sign a contract.
Two architectures, explained generically
Strip away brand names and there are really only two architectures in this category.
Above-joist integrated systems build the waterproofing into the deck surface itself. A sealing gasket sits between every deck board as it is installed, closing the gap that water would normally fall through. Rain hits the deck and sheds off the edge, the same way it runs off a roof. The joists, beams, and ledger underneath never get wet. Because the seal is part of the board installation, this only works on new construction; there is no way to slide a surface-level seal between boards that are already screwed down.
Below-joist retrofit systems, which include membrane-and-trough systems and retrofit tray systems, work from underneath. Water still falls through the deck boards exactly as it always did. A sloped tray, panel, or membrane hung beneath the joists catches that water and channels it to a gutter or downspout at the edge of the deck. These systems are popular specifically because they can be added to a deck that already exists, without touching the deck surface above. The trade-off is that the joists above the tray keep getting rained on through the board gaps, storm after storm, for as long as the deck stands.
A decision checklist
Work through these questions in order. Your answers will point you toward the right architecture faster than any spec sheet will.
- Are you building new or working with an existing deck? New construction opens up above-joist systems. An existing deck you do not want to tear apart limits you to a below-joist retrofit.
- Do you actually want the joists to stay dry, or just the space underneath? These are not the same requirement. If keeping the structure dry matters to you as much as keeping the patio below dry, that points toward an above-joist system.
- Do you want a single trade or two trades on the job? Above-joist systems are installed by the deck builder as one continuous build. Retrofit tray and membrane systems are typically a second trade, installed after or alongside the deck framing, which adds coordination and cost.
- Do you want a finished ceiling underneath the deck? Both approaches can support one, but the details differ. With dry joists, you can finish the ceiling with whatever material you like, on your own timeline. With a hung tray system, the tray itself is often the visible ceiling, seams and all.
- Is the waterproofing layer itself warranted, or just the boards? Ask this directly of any system you are considering. You want to know whether the part that actually stops the water carries a warranty, not just the decking on top of it.
- How much ongoing maintenance and inspection are you willing to take on? A system that keeps the framing dry needs little more than normal deck upkeep. A system that lets the framing get wet on every storm generally calls for periodic inspection of the joists for rot, especially in wetter climates.
How AmeriDex fits the above-joist choice
AmeriDex is an integrated above-joist deck drainage system built for new construction. Cellular PVC deck boards with a proprietary ASA cap lock onto the Dexerdry seal, an automotive-grade TPE gasket, as each board is installed. There is no field-applied caulk to fail and no separate tray to hang later. The result is a single continuous surface that diverts 100% of the rain off the deck before it reaches the joists, beams, or ledger. The substructure is a conventional 16 inch on-center joist layout, so there is no special sub-framing to plan for. The system is backed by a 25-year residential limited warranty and a 10-year limited commercial warranty, and boards ship in 12, 16, and 20 foot lengths across seven colors, with custom lengths available on request. For a deeper look at the mechanics, see the full above-joist deck drainage guide, or read the direct above-joist versus below-joist comparison.
How to get samples and a quote
If your project is new construction and you have decided the above-joist approach is right for you, the next step is simple. Request free samples to see the seven PVC board colors and feel the Dexerdry seal in person. Then submit your deck dimensions through the free quote form, and a regional dealer will return a written quote covering board count, accessories, and lead time. Builders and commercial projects can reach the AmeriDex team directly through the contact page for a project takeoff.