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Waterproof Your Deck Joists

Waterproof Your Deck Joists
By Guest Author: Trex RainEscape
October 24, 2023

Building a deck is not only a fun addition to your house but also a good investment. You will add both usefulness and value to your abode! Most decks in the United States have a wooden frame, no matter whether the surface is composite or wood. This frame or substructure is essential to protect, as you must ensure your deck will last a long time.

Trex Protect tape on deck joists
Trex Protect Joist Flashing Tape

Parts of Your Deck Substructure

You're busy having a good time on your deck, enjoying the sun and fresh air, so you may not think too much about what's underneath. Let's take a moment to see what's supporting your deck.

Under the surface boards, there are joists that run below them, usually perpendicular to the deck boards. Underneath the joists are beams that are just above the legs. The legs are vertical structures that anchor your deck into footings in the ground. There's usually little air circulation because all of this is built close together to brace your deck. That can cause a moisture buildup, which often leads to mold growth.

Trex Protect shields joists from moisture
Trex Protect flashing shields joists and beams from moisture

So, what can you do to prevent water from seeping in and moisture from lingering under your deck? Besides regularly checking your deck and keeping it clean, there are a few solutions. One of the best, easiest, and most worthwhile is applying flashing tape, such as Trex Protect, during construction.

What is Joist Tape?

Joist or flashing tape is thin, waterproof, and very flexible. This highly adhesive butyl tape is durable enough to withstand a wide range of temperatures. It's a simple and efficient way to protect your deck's joists, beams, and around-the-deck fasteners. Using joist tape will increase the length of your deck's life by preventing mildew, which can lead to rot and other issues. Trex Protect flashing tape additionally boasts a 25-year warranty.

Trex Self-Adhesive Butyl Tapes
Trex Protect Self-Adhesive Butyl Tapes

How Does Joist Tape Protect Your Deck?

When it rains, water can stay in the small, tight spaces in your deck's framework. As mentioned before, the wood can retain moisture with less air circulation throughout the underside of your deck. Flashing tape, when applied properly, will protect your wood. It's best to do this during the construction of your new deck. The tape can also be applied when making deck repairs. If you're replacing the surface of your deck, take this opportunity to use joist tape on top of the joists and beams to waterproof them.

Another benefit of joist tape is that it can waterproof around windows and doors. This also will protect your ledger board (the board against your house or building) so it stays dry. Trex Protect can help prevent moisture from corroding your deck screws and fasteners by shielding your fasteners from water damage. In fact, it can aid in holding the screws in place.

When an area of wood gets wet, it usually retains the moisture and does not completely dry if it's in a tight or covered area. Over the years, it will get moldy, which could eventually lead to wood rot. The deck will become structurally weak and then potentially be quite dangerous. Most deck mishaps, like collapses, are entirely preventable. According to NADRA (North American Deck and Railing Association), about half of decks in the U.S. need some maintenance and safety checks. Make sure your deck's substructure and supporting frame are protected from water damage by using a joist tape.

Water dmaaged deck joists
Water-damaged deck substructure

Why Butyl Tape? 

You've probably heard of different kinds of flashing tape on the market. The two main types generally are acrylic and butyl. Butyl tape, such as Trex Protect, has several advantages over acrylic tape. 

  • Butyl tape can withstand a variety of temperatures. Acrylic tape can get broken down by repeated hours of sunlight.
  • Butyl tape is flexible; it will form a perfect seal over deck joists, beams, and fastening hardware.
  • Butyl tape can be applied in almost any temperature.
  • Butyl tape is straightforward to apply, cuts cleanly, and sticks instantly. Trex Protect also has a non-skid surface that makes it safe for homeowners and contractors to walk on during installation.

Steps to Apply Flashing Tape

You or your contractors have the framework for your deck completed. It's looking good, and it's ready for the application of flashing tape so your substructure can have the longest life possible. Now is the time for Trex Protect butyl tape!

Trex Protect Joist Tape application
Trex Protect Joist Tape application

  1. Start by sweeping off your joists and beams. Take care to remove dirt, grass, leaves, and debris, like pine needles.
  2. Remove the tape's backing and pull along the length of the joist. Once you get to the end of the joist, slowly smooth down the tape with your hand.
  3. Cut the end of the tape using a utility knife or small blade.
  4. Smooth that over at the end while trying not to have too much overlap with the next piece

When applied with care, butyl joist tape will stretch out to provide a solid shield from moisture. The simple act of getting air bubbles out of the tape will help secure it in place.

Joist tape comes in several different widths. It's wise to estimate the materials you will need beforehand to make this job a breeze.

Extend the Lifespan of Your Deck

Joist or flashing tape will prolong the life of your deck. Besides waterproofing, this tape will help your deck frame stay sturdy and tolerate all kinds of weather. We've seen a lot of decks where the homeowner has forgone this step. Unfortunately, they have to make repairs by replacing damaged wood, and their deck's integrity can be compromised.

Trex Protect Joist Tape will help your deck and its substructure stay in top shape. After all the effort and investment, you've put into building a beautiful outdoor oasis, help your deck and yourself. Use butyl tape to protect and waterproof your joists and beams!

Thanks to Trex RainEscape for contributing this guest post. For the products referenced and more, shop the Trex Store at DIY Home Center. 

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