Is Joist Tape Necessary: What You Need to Know

In any home improvement project, there are many details to consider. The punch list can quickly get long. Thus, it’s natural for homeowners to ask whether something so small as joist tape is really necessary when building a new deck or replacing an old deck. After all, you don’t see it after construction, and it isn’t something you’ll brag to your friends about when they come to hang out on your deck.

But just as you wouldn’t leave out insulation from your walls or gutters on your roof, you wouldn’t leave off joist tape in deck building. Some details are absolute musts for the long-lasting protection and enjoyment of the construction.

Joist Tape: Why It’s Essential & When to Use It

Constructing anything from timber, especially outdoors, opens up a significant vulnerability. Even constructed with treated timber or built with dense timber such as ipe, a wood deck is eventually prone to mould, mildew, and rot. A composite deck means the deck boards are safe from rot, but if constructed on a timber substructure, the joists and bearers still need to be protected.

According to Decks.com, more than 90 per cent of a deck’s substructure starts to split and rot at around 8 to 10 years, while the deck boards (if made of composite decking) are usually warranted to last about 25 years. Ensure your deck is safely supported by its substructure for the life of the deck with minimal cost with joist flashing tape.

You can protect your deck joists, double joists, rim joists, bearers, the ledger board, and stringers with thin butyl tape. It can help you:

• Save on future maintenance and replacement costs.
• Increase the anticipated life of your deck.
• Improve your deck’s structural integrity.

Using joist tape is easier than you think. If you can DIY a deck, you can easily add this super protection. Peel-and-stick deck flashing tape allows the timber to breathe because it is applied as a cap directly on the top of the joists and bearers. The tape also protects screw holes from moisture by acting as a barrier.

What Joist Tape to Buy?

When choosing a flashing tape, be sure to consider these factors:

• Material type: Flashing tape typically comes in three types: acrylic tape (G Tape), butyl, and bitumen. Bitumen, made from petroleum and asphalt, will dry out over time. Butyl-based tape is superior to asphalt adhesive (like Grace Vycor) because it creates a tighter seal, has less high-temperature oozing, endures less stain, and is stickier. Butyl rubber tape also has many advantages over the acrylic-based tape. High-quality butyl tape, such as Trex Protect, is more rubbery than acrylic-based tape, allowing it to flow better around deck screws and fasteners, as well as covering galvanized metal joist hangers.  
• Easy Install: Any contractor or DIY homeowner will tell you to buy a butyl tape that is easy to install and requires little trimming. A self-adhesive butyl tape that lies directly on the boards requires minimum cuts with little overlap.
• Quality: When applying flashing tape to your bearers and floor joists, you want to be sure to purchase a tape that is not too thin and not too thick. With thin tape, you risk long-term durability of the tape. A thick tape can be difficult to install. You want a tape that will last as long as your bearers and joists. Trex Protect is available in tthree widths 50 mm x 20 m for joists, 100 mm x 20 m for double bearers and 279.4 mm x  15.2 m for rim joists.

Trex Protect comes with a 25-year warranty, so it lasts as long as the decking it supports. Acrylic tape comes with only a 300-day warranty.  

For an average size deck, measuring 3.6m x 7.3m, you’ll need five rolls of Trex Protect Joist Tape and one roll of Trex Protect Bearer Tape. For less than a £131 investment, the deck substructure can last as long as the decking it supports. To find out exactly how much Trex Protect Joist and Bearer Tape your project requires, use our Materials Estimator.

As you consider all the benefits of deck joist flashing tape — preventing rot and extending the life of your substructure — the answer to the original question is clear. Is Joint Tape Necessary? Yes!