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What is Roof Decking and Why is it Important? 

If you’re planning a commercial roof replacement—or even just looking into repairs—you might be surprised by how many different components go into making your roof system work. One of the most critical parts hiding underneath is something called roof decking. 

At Weather Shield Roofing Systems, we’ve been helping businesses protect their investments for over 40 years, and we’ve seen just how important a solid roof deck is to the long-term performance of your roof. In this article, we’ll break down what roof decking is, the types used in commercial roofing, when it needs to be replaced, how it affects your roof costs, and what codes you need to be aware of. 

Let’s take a closer look at this unsung hero of your roof system. 

What is roof decking?

Roof decking—also called roof sheathing—is the base layer that sits directly on top of your building’s structural frame. It’s the surface that your entire roofing system is built on. Whether you have a flat commercial roof with a membrane or a steep-slope metal system, your roof decking has to be structurally sound to hold everything up. 

Think of it like the foundation for your roof. If it’s weak, everything else on top is at risk. 

What types are used in commercial roofing?

There are a few different types of decking used depending on your building type, roof slope, and budget. In most commercial settings, the two most common types are:

1.) Sheet Decking (Plywood or OSB): This is the most common for commercial buildings with low-slope or sloped roofs. 

• • OSB (Oriented Strand Board) is made from compressed wood chips and is usually 7/16” thick. It’s cost-effective and widely available. 

• • Plywood is more water-resistant and comes in several thicknesses, like ⅜”, ½”, and ⅝”. It’s often used when greater strength is needed.

2.) Plank Decking (Older Buildings): Plank decking, made from 1×6 or 1×8 boards, is common in older commercial structures. If your building was constructed before plywood became mainstream, there’s a good chance it has plank decking. It’s solid but can present issues when gaps between boards widen over time. 

When does it need to be replaced?

Here’s the tough part: you usually won’t know the full condition of your decking until your existing roof is removed. That’s why roof inspections during a replacement are so important. 

We typically replace roof decking when: 

• • It’s rotted from long-term moisture exposure 

• • The wood is soft or spongy

• • There’s visible mold or warping 

• • It fails building code due to spacing or structural weakness

At Weather Shield, we don’t put new roofing over damaged or weak decking. If the deck isn’t strong enough to hold the new roof, it has to be replaced. That’s not just our rule—it’s required by building codes and the roof manufacturers.

How much does roof decking cost?

Here’s where it gets tricky—costs vary, and a lot of it comes down to how much needs to be replaced and what kind your building has. 

• • Plank decking is typically more expensive since it’s priced per linear foot and takes more labor to install. 

• • Sheet decking (OSB or plywood) is priced per sheet and is generally more cost-efficient, especially when replacing large areas.
• In 2025, wood is still pretty expensive, so decking can add a lot to your roof replacement cost. If your building has wood planks with big gaps, it might be cheaper to cover them with OSB or plywood instead of removing everything. The bottom line: your contractor won’t know the exact cost to replace the decking until they see what’s under your roof.

Does this matter for roof code compliance?

Roof decking isn’t just about supporting the roof—it’s about meeting legal and safety standards too. 

According to the International Building Code (IBC), any new roof system—especially one using asphalt shingles or other fastened materials—must be attached to solidly sheathed decking. That means: 

• If your existing deck is rotted, cracked, or spaced too far apart, it must be replaced. 

• For example, if you have plank decking with gaps greater than 1/8″, most manufacturers require replacement before installation can proceed. 

Some contractors try to skip this step to keep their price low and win the job. But that shortcut can void warranties, create long-term problems, and put your investment at risk. At Weather Shield, we always follow code and manufacturer guidelines—because cutting corners on decking can lead to bigger headaches down the road. 

Why you should care (even if you’re not the one on the roof)

If you’re a property manager, investor, or building owner, you might not ever see your roof decking—but its condition directly impacts your: 

• Roof lifespan: A weak deck can shorten the life of your entire system. 

• Roof leak risk: Water intrusion becomes more likely if the decking is compromised. 

• Roof insurance claims: Poor decking can lead to denied claims or failed inspections. 

• Roof cost savings: Replacing the right decking now can prevent much bigger repairs later. 

The Weather Shield Difference:

We’ve helped countless commercial clients avoid unnecessary costs by identifying decking issues early during routine roof inspections and through our Max Life Roof Care™ program. Preventive maintenance and thorough inspections save money—plain and simple.

Your roof is only as strong as what’s underneath it. In a commercial roofing system, the roof decking plays a big role in keeping your building safe, dry, and up to code. If you’re thinking about replacing your roof—or just want to avoid problems later—knowing about your decking helps you make smart, budget-friendly choices.

At Weather Shield Roofing Systems, we give honest answers and long-lasting roofing solutions to protect your building. If you have questions about your roof decking or want a full inspection, we’re ready to help.

Let us take the worry off your plate—because when your roof’s solid, so is your business.