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How Can I Protect Deck Joists From Water and Rot?

How Do I Keep My Deck Joists From Rotting?

The key to building a strong, long-lasting DIY deck that can last for generations is incredibly simple. Prevent harmful mold, water damage, rot, and insects from disrupting and harming your wood deck frame. This especially means protecting wood deck joists, beams, and ledger boards as they are structurally crucial to your deck space.

The most common deck framing material used throughout the United States is pressure-treated pine, also known as chemically-treated lumber. Treated lumber is engineered to be more resistant to mold and wear than non-treated wood but eventually without a barrier to prevent moisture, it will become weak and damaged.

Joist water damage can weaken the structural strength of your deck or porch and becomes unsafe for family and guests. Learning how to prevent deck rot, how to protect deck frame, and stop deck rot can improve your deck and help it last for generations.

          Add a layer of deck joist tape to your deck frame for a durable, long-lasting deck frame and substructure

How do I prevent deck rot?

There are two easy ways to prevent deck frame rot from taking over your family's outdoor space. Protecting the future and longevity of your deck joists and beams from water-damage and replacement is simple! One method involves preparing the deck frame in the beginning while the other is ongoing upkeep.

1. For existing older decks, one of the best ways to prevent and stop deck joist rot is to check your deck openings; and check often.

Every few weeks or so, stop to pull out any leaves, sticks, and other debris that gathers around and between deck boards. Be especially careful to inspect the areas where the decking crosses over deck joists.

When there's a build-up of debris like this in a small nook, moisture accumulates over time. As days turn into months and the temperature shifts and changes; that tiny bit of moisture becomes a huge problem for your deck joists and rot.

2. For new DIY deck construction or times when replacing old deck boards for new composite decking, take the time to add flashing and joist tape! Joist tape is an adhesive tape that is applied directly to the tops of deck joists and beams. Flashing joist tape acts as a barrier from moisture, preventing water from entering the tops of the lumber.

Joist flashing tape creates a watertight seal as it bonds to the treated lumber of the deck frame and eliminates any puddling. Essentially applied as a cap to the deck substructure, flashing tape protects by allowing the wood deck framing to continue to breathe on three sides while acting as a moisture barrier on top where condensation and water tend to collect and pool. It also prevents moisture from entering the wood framing through the screw holes and openings of common construction hardware by creating a deflecting layer of protection.

Read more about using deck joist tape to stop deck rot in the Decks 101: When, How, And Why To Use Joist Tape post!

Or learn more about how to install joist tape to stop deck rot and water damage in the Decks 101: How to Use Joist Tape post.

You can also consider installing a deck drainage system like the Trex RainEscape deck drainage system. These specialty under deck drainage lines protect the tops and sides of deck joists and beams from rainwater and debris. These are a great method on how to prevent rot while also creating a warm, dry underdeck space for rainy day enjoyment or seasonal storage!


More Deck Project Resources

Grace Vycor Plus Self-Adhering Flashing Tape
Starting at: $29.99
Acrylic Adhesive Flashing Tape by G-Tape
Starting at: $26.99
Trex Protect Non-Skid Butyl Tape is available in a 1-5/8 inch width for joists or in a wider 3-1/8 size for beams.
Starting at: $24.99