How Do I Waterproof Under a Deck?

After UnderCover System Install

Written by Robert Greaves

August 7, 2023

Deck waterproofing is an important part of deck installation, as water can be disastrous for any deck, especially a wood deck. While most homeowners know to take care of the top of the deck from moisture, it’s also important to waterproof under a deck as well. This goes double for people who own an elevated or roof deck. Waterproofing under your deck helps protect against runoff, which only waterproofing the top side won’t do.

If you’re looking to waterproof under a deck, there are several ways to successfully protect the underside of your outdoor space. Let’s take a look at your how-to waterproof under a deck options.

Before we get started, here are some helpful resources that you can learn more about UnderCover and our manufacturing of the materials we use.

Install a Membrane

A deck waterproofing membrane prevents water from reaching areas under the deck, such as a roof or open space. How this works is that the water drains straight through the deck and collects on the membrane versus in the wood, damaging and rotting your deck away. Under the deck is angled a bit to ensure the water drains away from your home and into a gutter. If you’re worried that the membrane will be an eyesore, they’re easily hiding from view by roofing material.

Ceiling Installation

To spruce up the outdoors while satisfying your search for how to waterproof under a deck, there is a stylish solution: waterproof ceilings. You can hang these water-resistant ceiling panels under your deck and they’ll prevent water from reaching underneath. If the panels are angled slightly, the water will move into a gutter or other drainage system. Installing a ceiling for deck waterproofing is a much more simple process than a membrane and there is no need to conceal it. If you have an eye for design, note that there are few styles available for the panels, though to waterproof under a deck there are few better options than waterproof ceilings if you have an open space beneath.


This is a two-part solution for how to waterproof under a deck.

  • Firstly, for deck waterproofing to be successful you’ll need to install flashing. Without this system then water from your roof can easily find its way inside various parts of the house and prevent rot in wood or plywood decks. If you have a door that connects the deck to the interior of your home, you’ll want pan flashing beneath the threshold to help control water at the entry point. Flashing for deck waterproofing is usually applied with caulk or roof cement and caulking you can do yourself depending on the method you’re using to waterproof under your deck.
  • Secondly, sealing can also be accomplished using a deck sealer or deck stain. Of course, you’ll still want flashing as neither a deck sealer nor stain is fully waterproof, but like hardwood floors in your home, you want to protect the wood itself from water and moisture.


No matter which method of deck waterproofing you choose, the primary concern is always runoff for how to waterproof under a deck. It’s the runoff that causes so much damage beneath your outdoor space. For drainage, you’ll want a drain in either the middle of your deck or a gutter alongside it. You can have multiple drains, but make sure you have a way to access them easily as a buildup can wreak havoc as well. Any material you use to waterproof under a deck must be slightly angled so that the water drains away from your home to ensure it runs into the drainage system. Pools of water collect easily under a deck and can seriously damage it.

Deck Waterproofing Experts

If you want to make sure your deck is safe from water damage and to ensure the job is done right, there is nothing wrong with contacting a professional to waterproof under a deck. We at PCF Custom Outdoor Living have specialized in under deck installations since our beginnings, having expanded into other services from there. We strive to provide you with the most professional experience possible and are committed to quality, reliability, communication, safety, tidiness, and integrity.

If you’re looking for how to waterproof under a deck, you’ve found your answer with PCF Group and we offer free estimates to make sure you know exactly the price range for deck waterproofing. We look forward to helping you keep your deck safe from rot and water!

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