Waterproofing an Upper Deck: Keeping the Space Below Dry

Deck Builders Seattle · Apr 23, 2026 · 3m

In this episode of Deck Builders Seattle, we look at waterproofing options for upper decks, especially when you want to use the area underneath as a patio, storage, or outdoor living space. In a rainy climate like Seattle, exposed framing and undersides can cause dripping, staining, and long-term moisture problems if they are not properly protected. We explain the basics of waterproof deck systems, what they can and cannot do, and how to plan for dry space below a deck.

We start by outlining the difference between simple water shedding and true waterproofing. Standard decking, whether wood or…