Retrofitting an under-deck drainage system is entirely possible for most existing decks—without having to dismantle your entire structure. The Ultimate Deck Shop has guided thousands of homeowners and contractors in transforming the often-unused space below decks into dry, functional outdoor living areas using proven systems that install from the underside. These solutions let you capture water that drips through deck boards, channeling it away to protect your joists and create valuable dry space beneath.
Several under-deck drainage systems are designed explicitly to work with existing decks. They mount to the underside of your joists, requiring only the space below and basic tools. This means decks in good structural condition can be upgraded to include safe, dry storage, sheltered patios, or livable under-deck rooms—saving time and considerable cost versus a full deck rebuild.
What Is an Under-Deck Drainage System?
An under-deck drainage system is a set of panels or troughs that forms a waterproof ceiling beneath your deck joists. Water passing through deck board gaps is captured by the system and directed to gutters or downspouts, keeping the area below dry and protected. This not only prevents moisture from accelerating joist rot but also turns previously unusable space into a sheltered retreat or storage spot for equipment, firewood, or patio furniture.
Benefits of Retrofitting Under-Deck Drainage
- Quick Installation: Most systems install in 1–2 days from below—no need to remove deck boards or disrupt your surface.
- Structure Protection: Adds a valuable moisture barrier that extends the life of deck joists, beams, and posts.
- Increased Useable Space: Creates a dry area for storage, play, or outdoor living—often at a fraction of the cost of an addition or shed.
- Visual Upgrade: Many systems offer finished ceiling options (white, tan, or textured) for a polished, inviting look under your deck.
Step-by-Step Installation: Retrofit on an Existing Deck
Installing an under-deck drainage system beneath an existing deck typically involves these major steps:
- Inspect Your Deck Structure: Check all joists and beams for signs of rot or damage. Repair as needed—using products like FastenMaster Deck Coat to seal and protect wood.
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Measure and Plan: Record joist spacing (usually 12–16 inches) and total deck width/length. Calculate the number of panels or lengths of rails required.
For specialty designs or to add outdoor living upgrades, this is a great point to consider integrating pergolas or shade structures for even more versatility. - Prepare the Underside: Clean the area to remove cobwebs or debris. Double check for clearance for slopes and drains.
- Install Main Rails or Troughs: Attach according to manufacturer instructions (often perpendicular to joists), with a 1–2% slope away from the house to encourage drainage.
- Fit and Attach Panels: Insert panels (or roll out troughs), snapping or interlocking them into the main rails. Overlap ends for a leak-tight fit.
- Add Gutters/Downspouts: Install at the system’s lowest point, ensuring water is directed away from your foundation.
- Test and Finish: Rinse the deck above with a hose to ensure proper drainage and check for leaks. Make adjustments as required.
- Add Skirting: For a complete look, consider finishing off with deck skirting or mesh to keep out animals and create a polished perimeter.
Comparison: Best Under-Deck Drainage Systems for Existing Decks
The Ultimate Deck Shop only recommends retrofittable (below-joist) under-deck systems for existing decks. Here are some of the top options, focusing on product availability, ease of install, and suitability for DIY or pro projects.
| System | How It Installs | Main Materials | Best For | Maintenance & Upgrades |
|---|---|---|---|---|
| ZipUp UnderDeck | Panels and rails snap to joist bottoms; no major surface demo | PVC panels + main rails | Quick DIY retrofits; clean finished look; inspectable ceiling | Easy access; panels unzip for wiring/inspection |
| DEK Drain Underside | Rubber membrane adheres below joists | Thick rubber | Custom-shaped decks; heavy duty protection | Low-maintenance, hidden look |
| TimberTech DrySpace (available by order) | Interlocking vinyl channels below joists | Extruded vinyl | Composite decks; seamless look | Needs periodic rinsing |
This ZipUp UnderDeck Main Rail system is highly popular at The Ultimate Deck Shop for its straightforward installation and maintenance-friendly design. Panels can be removed for access to wiring or lighting and swapped out with different colors or textures if you want to refresh your look in the future. You can learn more or order it directly from our ZipUp Underdeck product page.
Important Installation Tips
- Always ensure at least a 1–2% slope to prevent standing water. A common error is installing panels completely level, which can trap water and cause long-term damage.
- Use joist protection tape such as G-Tape before installation for extra rot resistance.
- Check that downspouts divert water well away from your home’s foundation.
- Leave a 1-inch air gap on the perimeter for airflow and to prevent mold.
How Much Does a Retrofit Under-Deck Drainage System Cost?
- Materials: For a 200 square foot deck, expect to budget between $800 to $1,600 for panels, rails, gutters, and hardware. Orders over $199 from The Ultimate Deck Shop ship free in Canada and US.
- DIY Tool Rental: Rent drills or saws if required from our tool rental service.
- Professional Installation: If you prefer pro install, the total cost for a 200–400 square foot space ranges from $2,000 to $4,000. For full managed install, see our Regina managed install service or contact the Saskatoon team.
Real-World Success: Homeowner Experience
Nicole N. from Regina upgraded her 20-year-old wood deck using ZipUp UnderDeck panels. The end result: a dry 250 sq ft patio space at a material cost of about $1,800, installed without the need for a full deck rebuild. Her finished project (and the seamless delivery service by our team) is highlighted in our Google reviews.
Common Problems and Mistakes to Avoid
- Insufficient Slope: Causes pooling, system sag, and quick deterioration. Use a level or string line to ensure proper angle away from the house.
- Poor Joist Prep: Always repair damaged wood and protect with a rot barrier before enclosing with a drainage system.
- Overtight Fasteners: Overdriving screws can crack PVC or vinyl panels, causing leaks and warranty issues.
- Inadequate Drainage: Gutters and downspouts should handle at least a 2-inch per hour rainstorm.
- Blocking Airflow: Skirting should allow for perimeter ventilation to avoid mold.
Comparing Under-Deck Waterproofing Approaches
It’s important to distinguish true under-deck drainage systems from waterproof coatings or simple tarps. For a deep dive on all waterproofing approaches (including tape, coatings, and above-joist systems), review our dedicated post What’s the best way to waterproof my deck so the space underneath stays dry for storage or a patio?
If you’re interested in related solutions to prevent rot, check out Stop Water From Rotting Your Deck Frame: Joist Protection Options Compared (Tape vs Coating) for further expert advice.
What Experts at The Ultimate Deck Shop Recommend
- Retrofit with ZipUp UnderDeck for easy DIY or pro upgrades with minimal deck disturbance.
- Prioritize joist protection (tape or brush-on coating) before sealing up the underside.
- For entertaining or dining under your deck, integrate lighting and consider pairing with pergolas and shade structures for superior shade and rain protection.
- Request a free 3D design or in-store consult for optimal material takeoffs.
- Pay close attention to gutter/downspout sizing and airflow for performance and long-term reliability.
Frequently Asked Questions
What is the easiest under-deck drainage system for DIYers?
ZipUp UnderDeck is typically the easiest for DIYers, with straightforward panel and rail assembly below joists. Panels can be removed for maintenance.
Can I add under-deck drainage to a deck with skirting or landscaping already in place?
Yes. Most systems install entirely from below. You may need to temporarily move skirting for gutter and downspout placement, but landscaping rarely needs major adjustment.
What if my joists have some rot?
All rot should be addressed before installing any enclosure. Use a protective sealant and always repair structural elements for safety and longevity.
Will I need a permit to add under-deck drainage?
Local regulations vary. In most Canadian municipalities, drainage systems do not require a permit if the structure isn’t altered, but always check your local bylaws.
Can these systems be used under stairs or angled decks?
Yes. Kits come with customizable panels. For complex shapes, it’s helpful to use a supplier that offers planning and takeoff support—available at The Ultimate Deck Shop.
How do I clean and maintain under-deck drainage systems?
Periodic rinsing of panels and gutters keeps everything clear. Removable panels like ZipUp make annual inspection simple.
What other upgrades pair well with under-deck systems?
Combining with privacy walls or shade structures (see pergolas and shade structures) delivers a truly multi-season entertainment zone.
Conclusion
If you want to reclaim the space beneath your deck—without tearing it apart—a retrofit under-deck drainage system is the expert-recommended solution. The Ultimate Deck Shop has extensive experience helping DIYers and contractors add these systems efficiently and reliably, using products such as ZipUp Underdeck and matching accessories. Whether you’re looking to create a dry patio, protect your investment, or simply maximize your outdoor space, our team can help you select the right system and provide design support every step of the way.
Visit The Ultimate Deck Shop in Regina or Saskatoon, or reach out online for expert advice, product guides, or free quotes. To further expand your outdoor living options, explore our Pillars & Shade Structures for seamless style and comfort additions.
