You hire a contractor, and you’ve got an elevated deck you love — it gives you enough space to store things and to utilize the space how you want. But then it rains. Now, you realize some steps were missed. It’s not waterproofed. You’re standing in a soggy mess, and I’ll be the first to tell you waterproofing after a deck is built is a thousand times harder than under-deck waterproofing during the build.
Done right, this process creates a dry, functional area under your deck where you can set up an outdoor kitchen, entertainment space, or a comfortable spot to hang out, even when the weather isn’t cooperating.
Why Under-Deck Waterproofing Makes Sense
Space under an elevated deck has serious potential. When you waterproof the area underneath your deck, you’re essentially doubling your outdoor living space. That’s extra square footage you can use for storage, entertaining, or relaxation without the cost of building an entirely new structure.
Beyond the additional space, waterproofing protects your investment. By planning and spending a bit more to waterproof the area under your deck, you’ll save yourself money and frustration.
Water that constantly drips through deck boards accelerates the deterioration of your deck’s structural components. Moisture can lead to wood rot and decay in joists and beams. A proper waterproofing system shields them — extending the life of your entire deck.
It’s a practical step and helps keep you and your guests comfortable. A good drainage system on an elevated deck is a no-brainer. We’re no strangers to elevated decks. A homeowner in Glen Cove recently had us demolish their old, unsafe staircase and add a railing so they could take in the views and enjoy the sunrise without having to worry about the safety of their deck (or having to look at chipped paint and rotting wood).
VIDEO OF GLEN COVE STAIR DEMOLITION
Understanding Your Waterproofing Options
Trex RainEscape
Trex RainEscape is a unique under-deck waterproofing system that uses a network of troughs and downspout construction to keep rain, spills, and snow melt from dripping through your deck boards.
A 25-year warranty backs the system, and you can do pretty much anything with it: add utilities like electric and gas lines to enhance your lighting and complete your outdoor kitchen. Most importantly, it’s built for under-deck waterproofing. It’s made up of vinyl troughs that hang between your joists, collecting water and directing it to gutters and downspouts.
The RainEscape system works well for new construction or major deck renovations. Installation involves sealing with butyl tape and trimming excess trough material with a utility knife or scissors to ensure that no bare wood is exposed. Once that’s done, you apply the Trex RainEscape butyl tape over all seams, starting at the ledger and working toward the downspouts.
Trex RainEscape can only be installed on a new deck build. If you’re looking to add deck drainage to an existing deck, try UpSide Deck Ceiling, ZipUP Underdeck Drainage, or my next suggestion instead. You’ve got to add waterproofing to your plan. When we do our free 3D designs for homeowners, we leave no stone unturned.
We plan it all out, building the deck of your dreams one plank at a time. We consider the top and bottom rails, the spindles (or balusters or infills), the top cap, the post skirt, the staircase, and, for elevated decks, the under-deck waterproofing, of course.
DEK Drain
DEK Drain systems are reliable but require professional installation (your under-deck waterproofing systems aren’t meant for the typical DIYer). They offer four distinct installation approaches to match different situations:
The Topside System is designed specifically for new deck construction. The panels attach to the top of your deck’s joists before any deck boards are installed. This setup creates a dry, functional space below while protecting the deck frame against moisture and deterioration. Each panel is pre-cut to width and length for each joist bay, eliminating waste and ensuring a perfect fit.
Custom-fabricated protective panels are the key to the Underside System. They’re made from thick rubber membrane material and attach to the bottom of your deck’s joists. The system captures water that slips through surface boards and installs easily without sealants or caulk, making it an ideal retrofit solution.
The Underside Recessed System fits up into the bays between joists, allowing you to install a finished ceiling underneath your deck. This approach opens up possibilities for lighting, fans, and additional electrical accessories.
Suppose you’re not ready for a full installation. In that case, DEK Drain’s Dog Ear Joist Flashing System can protect your deck frame against the elements while allowing for simple upgrades to a complete Underside system later without removing deck boards.
DIY Approach: EPDM Rubber Systems
For the advanced DIY enthusiast, EPDM (ethylene propylene diene monomer) rubber provides a cost-effective solution for under-deck waterproofing. EPDM rubber panels are flexible and easy to install. They create a waterproof barrier that moves water away from the bottom of your deck.
The basic concept involves hanging EPDM membrane between your joists to create water-collecting troughs. For the water to drain towards the gutter, the EPDM membrane has to droop between the joists. At the head of the joist bays (usually at the ledger), you’ll want about a 1- to 1 1/2-inch-deep trough.
Basically, you need to cut tapered strips of material that drape between the joists, with a slope from the house to the outside edge of the deck (hence, the taper in each strip). Staple these to the sides of the joist near the top edge. Then cover the top of each joist with a 3″ to 4″ strip to protect the wood and create proper water flow.
There are other routes to take, but you can look into it for yourself if you’re interested (there is a pretty good thread about it on the DIY Chatroom and a post about it in The Journal of Light Construction). I may write a post about it if more readers find it useful, but it’s not a holistic solution like Trex’s RainScape.
Maintenance and Cost Considerations
Any waterproofing system requires some maintenance. The good news is that most maintenance tasks are straightforward.
Keep the gutters and downspouts clean — things like that.
Clogged drainage defeats the purpose of even the best waterproofing system. Check seams and connections annually, looking for signs of separation, cracking, or other damage. Small problems are much easier and cheaper to fix than major failures.
Speaking of money, what’s the ROI on under-deck waterproofing?
DIY EPDM systems can cost as little as a few hundred dollars for materials for an average-sized deck. Professional systems, such as Trex RainEscape or Dek Drain, can cost thousands, but these costs will be factored into the final price. And if you choose our team, you’ll get a plan tailored to your budget. No interest and no payments for up to 18 months, that’s what we stand by. Why? Because nothing should stand in the way of you getting the outdoor space you love.
So let’s say you’re working with us.
We’ve already created a tailored plan that factors in the under-deck waterproofing for your elevated deck build, allowing you to utilize that extra space.
First, that extra usable square footage will add value to your property. If you ever sell, it will pay for itself because you will have doubled your outdoor functional space.
Next, factor in the protection value for your existing deck structure. Preventing water damage to joists and beams can save thousands in future repairs or premature replacement costs. I’ve seen our weather tear up hundreds of decks, especially those that didn’t invest a bit more up front.
Quick Summary
Under-deck waterproofing doubles your outdoor space. Many Long Island homeowners waterproof their elevated decks to add property value and create more room for entertaining. Some of the best options include the Trex RainEscape system for new construction, Dek Drain’s four professional systems (Topside for new builds, Underside for existing decks, Underside Recessed for finished ceilings, and Dog Ear Flashing for staged installation), or DIY EPDM rubber systems that offer cost-effective solutions for existing decks.
New construction gives you the most options, while existing decks work best with Underside professional systems or DIY EPDM approaches. The investment pays for itself.
