Does Joist Tape Really Work?

What is Joist Tape: A Brief Introduction

With joist, bearer & rim tape, you can protect your deck’s joists, double joists, rim joists, bearers, ledger boards, and stringers with a thin, waterproof membrane. In fact, deck flashing tape offers many benefits:

• Helping to reduce future maintenance
• Giving your timber deck a longer life — as a sealant protects your top decking boards, flashing tape protects what’s beneath and doesn’t have to be reapplied each year like stain or seal
• Protecting your deck’s structural integrity
• Holding deck screws and deck fasteners tighter and stronger

Why Use Joist Tape?

Water + timber = trouble. Wherever you find wetness, you’ll find timber that’s in danger of rotting.

Wait! I don’t have to worry about this if I used composite decking, right? After all, a composite deck made from recycled plastics doesn’t rot or need maintenance very much to keep it in great shape. The challenge is that most substructures, the bearers, and joists on which the deck boards sit are almost certainly made of timber. If left unprotected, your bearers, joists, rim joists, posts, and stringers can begin rotting in as little as 8 to 10 years, even with treated timber.

Moisture infiltrates your deck substructure through the spacing in your top boards. Every time rain falls, a gutter leaks or some other form of water runs through your decking onto your deck framing, this moisture begins to eat away at your deck. Creating a moisture barrier with deck joist tape allows you to waterproof your substructure and help it to last longer.

The other challenge with deck building is the galvanized metal fasteners and screws that hold the whole structure together. You need a barrier between the metal and the boards because today’s decking is preserved with ACQ; thus timber contains much higher concentrations of copper. When the zinc in galvanised fasteners touches ACQ, corrosion occurs. Joist flashing tape protects your timber with a thin membrane to guard against corrosive preservatives and holds in place your metal fasteners and screws.

Advantages and Disadvantages of Using Joist Tape

Besides a little extra time and money, there’s really no downside to using joist & bearer tape. Considering the cost of replacing a deck, the cost for flashing tape is tiny!

You can DIY the tape or have a pro install it. This quick animated video shows how simple it is to ensure a tight seal on the top of the joists and around screw holes. If you use quality butyl tape you’ll see minimal wrinkling and tearing, ensuring an easier install.

What to Look For in Joist Tape

When selecting a joist tape, consider these three critical factors:

1. Type of material: Joist tape primarily comes in three materials: acrylic, asphalt, and butyl. If you choose a butyl-based tape, you’ll be pleased with its superior protection and durability. Butyl is stickier than asphalt adhesives and endures a wider range of temperatures.
2. Ease of install: Today’s joist tape is self-adhesive, making it easy to install. With Trex Protect butyl tape, you’ll have less trimming and a better fit on your boards. It’s not too thick, which would be difficult to install, or too thin, which can easily tear.  Press firmly onto the boards to ensure good adhesion, and use a hand roller to smooth out any bubbles.
3. Cost of the tape: Butyl tape costs little and gives you big peace of mind. A good manufacturer will back their product: that’s why Trex Protect comes with a 25-year warranty. Use this materials estimator to determine how much tape you will need to buy.

Placed on the tops of the substructure before deck boards are added,  deck flashing tape must be installed during construction on a new deck. When it’s time to replace your old deck, make sure flashing tape is part of your construction plan.

Does joist tape really work? Look at how a quality butyl tape holds up in a three-month water test. The answer is definitely YES! If you’re a homeowner planning a deck as a home improvement this season, make sure you include joist tape.