What is Roof Decking?

Is it time for a roof replacement? Do you keep hearing about roof decking?

Your roof is a combination of different roofing materials and components that come together to protect your home from the elements. While all the materials are important to your roof, roof decking is the foundation.

I say foundation because it's literally the groundwork for your entire roof system. That’s why it's important to understand everything there is to know about roof decking, from the types to how much it costs.  

For over 35 years, Bill Ragan Roofing has provided homeowners the information they need to feel confident signing their roof estimates. So, let's break down the things homeowners must know about roof decking when getting a new roof. 

By the end of this article, you'll have the answers to:

• What is roof decking?
• Does roof decking get replaced during a roof replacement?
• How does a roofing contractor replace roof decking?
• How much does roof decking cost?

What is roof decking?

Roof decking (or roof sheathing) is the wooden boards that make up the framing of your roof. I like to call it the foundation of a roof system because the boards are what your entire roof is installed on.

There are 2 types of roof decking: plank decking and sheet decking. Both are still on homes today, but sheet decking is now the most commonly used type in the United States. 

Plank decking

Plank decking was the standard for roof decking before the invention of plywood. This roof deck is made up of elongated and rectangular wooden boards (planks) that come in either 1x6 or 1x8.  

Even though it's not as common as it used to be, you’ll still find plank decking on older homes. However, whether or not plank decking is reused (if needed) when replacing a roof depends on a couple things (more on this later).

Sheet decking

Sheet decking (or sheathing) is exactly what it sounds like, flat sheets of wood, either plywood or OSB. Both types of sheet decking are great options, and it really just depends on a roofer's preference. 

OSB (oriented strand board) is the most common type of decking used on roofs today. It’s made up of wood chips/strips compressed together to form a flat 7/16” sheet.

Plywood comes in several different thicknesses (⅜”, ½”, ⅝”, and ¾”) depending on the span of the rafters. While OSB is the most common, plywood is still very much used on homes today. 

As I said, both types of sheet decking are great options. It just depends on your roofer's preference, budget, and the availability of wood.

Does roof decking get replaced during a roof replacement?

If any of your roof decking’s integrity is compromised or there are signs of rotting, the wood must be replaced before installing your new roof. However, there's no guarantee you'll to have to replace your decking during a roof replacement. 

In most cases, there are a few boards that have to be replaced. Just know that there's no way to determine how much roof decking needs to be replaced until after tearing off the old roof.

But no matter what, replacing any compromised decking is absolutely crucial to your roof's longevity and home's health. In fact, there are even building codes set forth by the 2018 International Residential Code about replacing decking. 

R905.1: Roof Covering Application

The first code doesn't have to do with decking itself. Instead, it focuses on proper roof installation.

As of 2021, shingle manufacturers' added installation instructions stating that plank decking with more than an 1/8” gap between the planks must be replaced before roofing materials can be nailed on. This simply means that plank decking with gaps larger than an 1/8" must be replaced before installing shingles. 

If they aren't replaced, leaks will happen if nails get between the gaps and your roof technically isn't installed properly. Even worse, your roof isn’t up to code and any warranty provided by the manufacturer is voided.

R905.2.1:  Roof Sheathing Requirements

While the first code revolves around following instructions and planks, the next one is actually about roof decking in general. Simply put, roof decking must be considered "solid" before installing shingles. 

This code means that entire roof deck must be able to withstand and hold your new roof when it’s installed. So, any rotten or compromised decking, must be replaced before your roof is installed according to codes.

How does a roofing contractor replace roof decking?

Roofers replace roof decking a few different ways, depending on the situation. If they have to change out boards, they'll remove the compromised area and install the same type (if available) in its place. 

This happens in both large and smaller affected areas, but the important thing is that the rafters are hit. Now, there are rare cases where the entire roof has to be re-decked. 

If it's sheet decking, they'll remove the old sheets and just lay new sheets over the rafters. However, plank decking is different if there are too many planks with gaps or rotting is too widespread.

Instead of ripping up boards, they'll nail over the planks with a type of sheet decking. This not only saves time, but also ensures that there's a solid roof deck all the way around. 

How much does roof decking cost?

Roof decking’s cost is hard to nail down because of the fluctuation of wood prices. Wood prices are pretty high right now in 2025, which means it could add a large amount to your roof investment if a lot has to be replaced.

However, I can at least give you an idea of how much it would cost to replace roof decking per piece (for labor and materials). Plank decking will cost around $3.50 per linear foot installed, while sheet decking will cost around $90 per sheet installed. 

Keep in mind, that plywood is more expensive than OSB, so sheet decking's cost depends on the type. At the end of the day, you won’t know the cost of your roof decking until your roofing contractor determines the type and how much needs to be replaced.

However, they should always a have line item or clause stating how much decking will cost if they have to replace any. 

What others materials and components make up a roof?

Now you know what roof decking is, the types, if it gets replaced when getting a new roof, and more. Decking is a crucial part of your roof system and must be in good condition to ensure your home is protected. 

But roof decking is just one important piece of the puzzle for a roof replacement. In fact, it's just the first layer. 

So, you need to know the rest of the roofing materials that make up your roof before signing or buying anything. That's why I wrote another article breaking down the 9 roofing materials and components that should be part of every roof system. 

Check out 9 Materials Included With Your Roof Replacement to learn the crucial layers and components that make up a roof.