Is Under Deck Waterproofing Worth It? | Petra Decks Seattle
If you have a raised or second-story deck, you’ve probably noticed how much unused space sits underneath it. Rain drips through the decking, leaving the area below damp and unusable most of the year. That’s where under deck waterproofing comes in—a system designed to capture water and divert it away from the framing. But is it really worth the cost? Let’s look at what it does, when to consider it, and why many Seattle homeowners are choosing to add it.
What Under Deck Waterproofing Does
Under deck waterproofing systems create a barrier beneath your decking boards. Instead of water soaking the joists or dripping below, the system channels it toward gutters and downspouts.
This does two main things:
Keeps the structure dry and extends the deck’s lifespan.
Creates dry, usable space below for storage, outdoor furniture, or even a covered patio.
In a rainy climate like West Seattle, Issaquah or Sammamish, it can completely change how you use your backyard.
Benefits of Adding Waterproofing
1. Longer Structural Life
Moisture is the biggest threat to wood framing. A waterproofing system keeps joists, beams, and hardware dry, slowing rot and corrosion. This adds years to your deck’s lifespan.
2. More Usable Outdoor Space
You can turn the area below into a sitting space, outdoor kitchen, or storage area for garden tools and furniture. Many homeowners in Issaquah and Snoqualmie use it to create a sheltered patio for year-round use.
3. Low Maintenance
Once installed, under deck drainage systems require minimal maintenance—just seasonal cleaning of the gutters and downspouts.
4. Increased Home Value
A dry, finished under-deck area adds functional square footage. Buyers notice improvements that make outdoor living more usable in the Pacific Northwest climate.
When It’s Worth the Investment
Under deck waterproofing makes the most sense when:
You have a raised deck with at least 6 feet of clearance below.
You plan to use or finish the space underneath.
You’re already replacing the decking or framing, making installation easier and more cost-effective.
If your deck is older or you’re already planning a rebuild, it’s an ideal time to add waterproofing before new boards go down.
Cost and Value
The cost typically ranges between $6–$10 per square foot, depending on the system and accessibility. While it adds to the project budget, it also prevents costly water damage and expands your usable outdoor space.
In short: you’ll spend a little more now but save on repairs and enjoy a dry area that can be used year-round. For most homeowners in Seattle, Kent, or Redmond, that trade-off is well worth it.
Professional Installation Matters
Proper installation is critical. A poorly installed drainage system can trap moisture instead of diverting it.
Final Thought
Under deck waterproofing isn’t just an upgrade—it’s an investment in longevity and comfort. In Seattle’s wet climate, it protects your framing, reduces maintenance, and adds livable space below your deck.
If you’re planning a deck rebuild or replacement in King County, ask Petra Decks about adding a waterproofing system. It might be the smartest feature you install.
Contact Petra Decks today for a free consultation and design estimate.