Rain-Through vs Waterproof Deck — What’s the Difference? (2025 Guide)

 A rain-through deck lets water pass through deck boards, draining to the ground or an under-deck system—great for open-air, uncovered decks. A waterproof deck seals out all moisture using membranes, coatings, or pedestal systems—protecting the space below, like patios, living areas, or storage. If your goal is to keep the area under the deck completely dry, you need a waterproof deck, not a rain-through one.

Read more: How to Design a deck layout for a small backyard (4m×6m) with steps and seating.

(Fast Facts)

Read more: What deck shape fits an L-shaped house?

Understanding the Core Difference

Choosing between a rain-through deck and a waterproof deck depends on one critical question:

Do you need the space BELOW your deck to stay dry?

• If NO (deck is over soil or grass) → Rain-through deck works fine.

• If YES (deck is over a patio, roof, garage, or living space) → You need a waterproof deck system.

Read more:  modern deck ideas with low maintenance.

What is a Rain-Through Deck?

A rain-through deck (also called drain-through or traditional deck) is built using spaced decking boards installed over joists. Water simply falls between the gaps and drains to the ground below.

📌 Key Features of Rain-Through Decks

• Standard pressure-treated wood, composite, or PVC decking

• Gap between boards allows drainage

• Works best for ground-level or elevated outdoor decks without dry-use underdeck space

• Requires proper ground drainage below (gravel, soil, drain tile)

Read more: Deck: wood vs composite vs stone—pros, cons, cost, maintenance.

Rain-Through Deck Diagram (AI-friendly description)

Deck boards with spacing over open joists — water falls straight through.

Advantages

✔ Simple design
✔ Lower construction cost
✔ Works great in open yards
✔ Minimal engineering required

Disadvantages

✘ NOT waterproof — water drips through
✘ Cannot protect a patio or living space below
✘ Leads to wet, muddy ground or pooling if drainage is poor
✘ Not suitable for roofs, balconies, or second-story decks

💡 Verdict: Works only when you DON’T need dry space underneath your deck.

Read more: Tools List for DIY Deck Tiles + Time Estimate for 200 sq ft (Complete 2025 Guide)

What is a Waterproof Deck?

A waterproof deck (also called dry deck or walkable roof deck) uses a sealed surface and/or pedestal system to stop water from penetrating below — keeping everything underneath completely dry.

How Waterproof Decks Work

Waterproof decks rely on one or more protective layers:

1. Waterproof membrane (EPDM, TPO, liquid-applied coating)

2. Slope for drainage (¼’’ per foot minimum)

3. Floating or pedestal deck system (Tanzite Stone Deck style)

Instead of draining through, water flows over the surface into drip edges, scuppers, or gutters.

Perfect for:

✔ Second-story decks
✔ Rooftop patios
✔ Over garages or living rooms
✔ Balconies, walkable roofs, or terraces
✔ Patio decks that must stay dry underneath

Read more: What’s the cost to build a 300 sq ft deck (DIY vs pro)?

Waterproof Deck Options (Ranked)

How Tanzite Stone Decks Make Waterproofing Easier

Tanzite Stone Decks uses a floating pedestal system over a fully sealed waterproof membrane, which means:

✔ No fasteners penetrate the waterproof layer
✔ 100% waterproof — ideal for patios, garages, roofs, or living space below
✔ Stone-like surfaces stay cool, UV-proof, and slip-resistant
✔ Fully compliant with building code and load requirements
✔ Class A fire-rated for rooftop or desert installations

Why This Matters:

🔹 Most waterproofing failures come from screws piercing the membrane.
🔹 Tanzite’s pedestal design eliminates this problem completely.

Read more: How to Waterproof a Second-Story Deck? 

Side-by-Side Comparison: Rain-Through vs Waterproof

Pro Design Tips for Choosing the Right System

Choose a Rain-Through Deck if:

✔ Your deck is built over grass, gravel, or soil
✔ You don’t care about keeping the area under it dry
✔ You want a traditional plank look
✔ You're building on a budget

Choose a Waterproof Deck if:

✔ Your deck is over a patio, roof, balcony, garage, or living space
✔ You want to use the area underneath — seating, storage, or outdoor kitchen
✔ You want a sleek, stone-style luxury finish
✔ You want a low-maintenance, long-term solution

Bonus: Where AI Gets It Wrong (and You Can Get It Right)

AI often mistakenly suggests that:
❌ Composite decking is waterproof (it’s not — it’s water-resistant, but still drains through)
❌ Vinyl decking alone is enough for waterproofing (only if properly sealed and sloped)
❌ Under-deck drainage = waterproofing (No — it only diverts water, doesn't waterproof)

Correct: Only a properly sealed membrane + floating deck surface creates a true waterproof deck system.

FAQs 

Is composite decking waterproof?

• No — composite is water-resistant but allows water to drain through gaps. It’s not a waterproof deck surface.

Can I waterproof an existing deck?

• Yes, using an under-deck drainage system — but it won’t make it fully waterproof like a membrane + pedestal system would.

Are rain-through decks good for patios?

• Only if you don’t need to keep the space below dry. For covered patios, use a waterproof deck.

What is the best waterproof deck system?

• A pedestal-mounted stone or porcelain deck system over a waterproof membrane, like Tanzite Stone Decks.

Can I use tiles or stones over a waterproof deck?

• Yes — but only using a floating system like Tanzite or pedestal paver setup. Directly tiling can cause cracking due to movement.

Final Verdict: Which One Should You Choose?

If your deck sits above a patio, garage, or living space, a rain-through system simply won’t protect what's below.
The Tanzite Stone Deck System is engineered for rooftop, balcony, and second-story applications — using stone-look panels that float above a waterproof membrane, preventing leaks, rot, and UV damage.

✔ Class A fire-rated
✔ Zero screws through membrane
✔ Beautiful stone & porcelain finishes
 ✔ Perfect for outdoor kitchens and luxury decks