Do You Need Joist Tape on Pressure Treated Wood for Your Deck?

joist tape on pressure treated wood

joist tape on pressure treated wood

joist tape on pressure treated wood

joist tape on pressure treated wood

Why This Question Comes Up So Often

One of the most common things homeowners say during a deck project is:

“Isn’t pressure treated lumber already protected?”

It’s a fair question.

Pressure treated lumber is designed to resist rot and insect damage, so at first glance, joist tape can feel unnecessary.

But after years of building decks in North Dakota and Minnesota, here’s what we’ve learned.

The part of the framing that fails first usually is not the middle of the board.

It’s the top edge.

What Pressure Treated Lumber Actually Protects Against

Pressure treated lumber is infused with preservatives that help slow down rot and decay.

That protection absolutely matters.

But it does not make the wood waterproof.

Moisture can still sit on top of the joists, especially beneath composite decking where airflow is reduced.

That’s where problems begin over time.

Why the Top of the Joist Matters Most

The top edge of a joist takes the most abuse.

• Rainwater sits there.

• Snow melts there.

• Fasteners penetrate there.

Every screw or hidden fastener creates a small opening where moisture can work its way into the lumber.

Over time, repeated wet-dry cycles start breaking the wood down from the top.

This is especially common under composite decking because the boards above hold moisture longer than traditional wood decking.

What Joist Tape Actually Does

Joist tape acts like a protective barrier over the top of the framing.

It helps:

• Reduce water penetration

• Seal around fasteners

• Protect vulnerable areas from long-term moisture exposure

Think of it this way.

Pressure treated lumber protects the board itself.

Joist tape protects the most vulnerable part of the board.

That combination is what helps extend the life of the framing.

Why This Matters More Under Composite Decking

Composite decking lasts a long time.

That means the framing underneath needs to last too.

We’ve seen situations where composite boards still looked good while the framing below had already started deteriorating.

That’s not a conversation any homeowner wants to have.

Joist tape helps slow down one of the biggest causes of premature framing failure.

The Midwest Climate Makes This More Important

Freeze-thaw cycles are tough on outdoor structures.

In Fargo and throughout the upper Midwest, decks deal with:

• Heavy snow

• Spring melt

• Summer heat

• Repeated expansion and contraction

That constant moisture movement creates stress on framing over time.

Small details like joist tape matter more in climates like ours.

Is Joist Tape Required?

In most cases, no.

It’s usually not a code requirement.

But there’s a difference between what meets minimum code and what helps a deck last longer.

After 37 years in the industry, we see joist tape as one of those upgrades that simply makes sense for long-term performance.

A Real Example From the Field

We’ve torn apart older decks where the framing looked solid from underneath, but the tops of the joists were badly deteriorated once the decking came off.

The damage almost always started where water sat around fasteners year after year.

On decks where joist tape had been used, the difference was noticeable.

The framing held up much better over time.

Is It Worth the Extra Cost?

Compared to the total investment of a deck project, joist tape is relatively minor.

But replacing framing later is not.

That’s why many homeowners decide it’s worth doing while everything is exposed during construction.

It’s one of those things that is inexpensive to add now and difficult to add later.

Key Takeaways

• Pressure treated lumber is resistant to rot, but not waterproof

• The top of deck joists is where moisture damage usually begins

• Joist tape helps protect framing from long-term water exposure

• Composite decking can trap moisture longer than wood decking

• Freeze-thaw conditions in North Dakota make framing protection even more important

Final Thought

Joist tape is not the most visible part of a deck project.

Most homeowners will never see it again after the deck boards are installed.

But years later, it can make a real difference in how the framing underneath holds up.

Sometimes the best upgrades are the ones nobody notices until they matter.