What is Roof Sheathing?

Is it time to replace your roof? Do you keep hearing about roof sheathing, but don't fully understand what it is, if it needs replaced, etc.?

When looking up at a roof, most homeowners see shingles and think that’s the extent of it. But the truth is, a roof system is so much more than what you can see from the street. 

In fact, just like your home has a foundation to sit on, so does your roof system. That’s where roof sheathing comes in. 

But what is it? Are there different types? Does it get replaced during a roof replacement? 

For over 35 years, Bill Ragan Roofing has educated homeowners on everything roofing, even the basics. That’s why I’ll answer the questions above and more. 

This article covers the following:

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

What is roof sheathing?

Roof sheathing (more commonly known as roof decking) is the wooden framing of your roof. I like to call it the foundation of a roof system because the wooden boards are what your entire roof is installed on.

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

Plank sheathing

Plank sheathing was the standard sheathing for roofing before the invention of plywood. A rood deck with plank sheathing 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 sheathing 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 sheathing

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

OSB (oriented strand board) is the most common type of sheathing 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 sheathing are great options. It just depends on your roofer's preference, budget, and the availability of wood. 

Does roof sheathing get replaced during a roof replacement?

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

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

But no matter what, replacing any compromised or rotting wood 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 sheathing.

R905.1: Roof Covering Application

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

As of 2021, shingle manufacturers' added installation instructions stating that plank sheathing with more than an 1/8” gap between the planks must be replaced before roofing materials can be nailed on. This simply means that any plank sheathing 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 sheathing 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 sheathing, must be replaced before your roof is installed according to codes.

How does a roofing contractor replace roof sheathing?

Roofers replace roof sheathing 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 sheathing cost?

Roof sheathing's cost is hard to nail down because of the fluctuation of wood prices. Wood prices are pretty high right now in 2026, 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 sheathing will cost around $3.50 per linear foot installed, while sheet sheathing will cost around $90 per sheet installed.

Keep in mind, that plywood is more expensive than OSB, so the final cost depends on the type. At the end of the day, you won’t know the cost of your roof sheathing 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 it will cost if they have to replace any sheathing per board.

What are the other components of a roof system?

Now you know what roof sheathing is and everything you need to know about it. While roof sheathing is a crucial part of your roof system, it’s just one piece of the puzzle. 

Not only are the components important to your roof, but they also matter to your wallet and roof's longevity. That’s why you need to know the rest of the roofing components that make up your roof.

Because of this, I wrote another article breaking down all the roofing components and materials that make up a residential roof system. 

Check out 10 Materials Included With Your Roof Replacement to learn the crucial components that make up a roof.