Top Tips for Waterproofing Your Deck

A deck is a valuable extension of your home, providing a space for relaxation, entertaining, and outdoor enjoyment. However, constant exposure to the elements—including rain, snow, and temperature fluctuations—can lead to moisture damage, warping, mould growth, and structural decay. Without proper waterproofing, even the most well-built deck can suffer from rotting wood, loose boards, and premature aging.

Waterproofing is essential to extend the life of your deck, maintain its appearance, and protect your investment. Whether your deck is made of natural wood or composite materials, applying the right protective measures can prevent costly repairs and ensure long-term durability.

Related Article: How Much Does It Cost to Resurface a Deck?

Choose the Right Decking Materials

The type of decking material you choose plays a significant role in how well your deck resists moisture. Some materials are naturally more water-resistant, while others require additional sealing and maintenance to prevent damage.

Pressure-Treated Wood

• Pros: Naturally more resistant to rot, insects, and moisture due to chemical treatment.
• Cons: Still requires regular sealing and staining to prevent water absorption and surface deterioration.
• Best Use: Ideal for homeowners who prefer the look of real wood and are willing to commit to routine maintenance.

Composite Decking

• Pros: Made from a blend of wood fibres and plastic, composite decking is naturally water-resistant and won’t rot like traditional wood.
• Cons: While lower maintenance, composite decks still need periodic cleaning to prevent mould or mildew buildup in shaded or damp areas.
• Best Use: Perfect for homeowners looking for a low-maintenance decking option with strong moisture resistance.

Exotic Hardwoods (Ipe, Teak, or Mahogany)

• Pros: Contain natural oils that repel water and resist decay better than standard wood.
• Cons: Still require occasional oil treatments or sealants to maintain their rich colour and water-resistant properties.
• Best Use: Great for high-end decks where homeowners want natural beauty with enhanced durability.

Selecting the right decking material is the first step in waterproofing, but additional protective measures are necessary to ensure long-term performance.

Related Article: Deck Types 101: Your Guide to Different Types of Decks

Apply a High-Quality Sealant or Stain

One of the most effective ways to waterproof a wood deck is by applying a high-quality sealant or stain. These treatments create a protective barrier, preventing water from soaking into the wood and causing damage over time.

Sealants

Sealants are clear or lightly tinted coatings designed to repel water while preserving the natural wood grain.  They prevent moisture absorption and reduce the risk of warping, cracking, or rotting.

Best for: Homeowners who want to retain the natural colour of their wood deck while adding water protection.

Stains

Stains add colour and UV protection while also sealing the wood against moisture. Available in transparent, semi-transparent, and solid finishes, stains provide varying levels of protection and colour enhancement.

Best for: Homeowners looking to enhance the look of their deck while providing extra durability against moisture and sun damage.

Reapplication

Both sealants and stains need to be reapplied every 1-3 years, depending on exposure to sun, rain, and foot traffic. Regular maintenance ensures that the deck remains protected, visually appealing, and resistant to water damage.

Applying a high-quality sealant or stain is an essential step in deck waterproofing, ensuring that moisture doesn’t seep into the wood and cause long-term damage.

Install Proper Drainage Systems

A well-designed drainage system is essential for preventing water buildup and structural damage to your deck. Without proper drainage, moisture can collect on the surface or beneath the deck, leading to wood rot, mildew growth, and foundation issues.

Implementing effective drainage solutions will help protect your deck from long-term water damage.

1. Ensure gaps between deck boards: When installing a deck, leaving small gaps (⅛ to ¼ inch) between boards allows water to drain properly instead of pooling on the surface.
2. Add an under-deck drainage system: Installing an under-deck drainage system can prevent water from accumulating below and damaging the supporting structure.
3. Use angled slopes to direct water away: A deck should be built with a slight slope (around 1/4 inch per foot) to ensure that water naturally flows away from the house and deck foundation.
4. Use waterproof membranes or coatings: These waterproofing solutions are especially useful for wood decks and multi-level decks with living spaces below.
5. Apply liquid rubberized coatings: Best suited for wooden and concrete decks, these coatings also provide UV resistance and slip protection.
6. Install vinyl deck membranes: Vinyl deck membranes are durable, flexible sheets that fully seal the deck surface against moisture. These membranes are great for balcony decks, rooftop decks, and second-story decks, preventing water from leaking into the structure below.
7. Consider underlayment waterproof barriers: These barriers are often used beneath composite decking or wood decking for added moisture protection.

Related Article: Can Decks Be Installed on Uneven Ground or Slope?

Keep Your Deck Clean and Well-Maintained

Even with proper waterproofing, regular maintenance is necessary to keep your deck in the best possible condition. Moisture, dirt, and debris can break down protective coatings over time, leading to water damage and mould growth if left unchecked.

1. Remove debris and standing water
2. Power wash or scrub your deck regularly
3. Inspect for cracks, warping, or early signs of water damage

Ensure Proper Flashing and Joist Protection

Waterproofing isn’t just about protecting the surface of the deck—the underlying structure needs just as much attention. Flashing and joist protection play a critical role in preventing water damage to the deck frame, fasteners, and connection points.

Install Metal Flashing for House-to-Deck Connections

• Flashing is essential where the deck connects to the house, preventing water from seeping behind the ledger board.
• Aluminum, copper, or galvanized steel flashing helps divert water away from vulnerable areas, reducing the risk of wood rot and interior leaks.
• If your deck doesn’t have flashing, consider adding or replacing it to prevent long-term damage.

Use Joist Tape to Protect Structural Components

• Joist tape is an easy-to-apply, waterproof adhesive that seals the tops of deck joists, beams, and ledger boards.
• It helps prevent trapped moisture, extending the life of the wood and reducing the risk of rot in hidden areas.
• Joist tape is especially beneficial for pressure-treated lumber, which can still absorb water over time.

Reinforce Vulnerable Areas with Additional Weatherproofing

• Areas near stairs, railings, and support posts are more prone to water damage and should be inspected regularly.
• Consider sealing screw holes and gaps with waterproof caulking to prevent water infiltration.
• Ensure that all fasteners and hardware used in deck construction are rust-resistant and designed for outdoor exposure.

Adding flashing and joist protection significantly improves a deck’s structural integrity and extends its lifespan by keeping hidden moisture damage at bay.

Related Article: How to Clean Composite Decking

Signs You May Need Professional Waterproofing Services

• Soft, spongy, or weakened wood.
• Visible mould or mildew buildup.
• Cracks, warping, or separation in boards.
• Water pooling or poor drainage.

Protect Your Deck for Long-Lasting Enjoyment

Waterproofing is one of the most important steps in preserving the beauty, durability, and longevity of your deck. While DIY waterproofing solutions can be effective, professional services provide long-term durability and expert protection.

If you’re looking for high-quality deck waterproofing in Toronto and York Region, Green Side Up offers expert solutions to keep your outdoor space safe and weather-resistant. We also offer pool deck services to enhance durability, safety, and aesthetics to ensure a visually appealing outdoor space.

Contact Green Side Up today to learn more about professional deck protection and maintenance services!