What is Roof Sheathing? (What You Need to Know About It)

When looking up at a roof, you probably 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 30 years, the team at 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 roof sheathing is. 
• When roof sheathing requires replacing. 
• The building code that impacts roof sheathing. 
• How roof sheathing impacts the cost. 

What is roof sheathing?

Roof sheathing (also called roof decking) is the wooden boards that make up the framing of a roof system. These boards are what your shingles and other roofing components are installed directly on.

There are two types of roof sheathing, plank and sheet. 

Plank sheathing

Plank sheathing was used before the invention of plywood. However, you’ll still see planks on homes today. 

Plank sheathing is made up of elongated and rectangular wooden boards that come in 2 different sizes, 1x6 or 1x8. While plank sheathing used to be the default type, sheet sheathing has taken its place as the go to type used for roof replacements today. 

Sheet sheathing

Sheet sheathing is wide, flat sheets of wood. The two types of sheet sheathing are plywood and OSB. 

(OSB roof sheathing)

OSB (oriented strand board) is the most popular choice for sheathing today. It’s made of wood chips and strips that are compressed together to form a flat 7/16” sheet. 

(Plywood roof sheathing)

Plywood has several different thicknesses (⅜”, ½”, ⅝”, and ¾”) depending on the span of your rafters. While OSB is the more commonly used, plywood is still a popular choice to use on homes today.

Which one you get depends on your budget and, more importantly, the availability of the wood. 

3 things that you need to know about roof sheathing

Now you know what roof sheathing is and the two types. But there are still a few more things you need to know about roof sheathing. 

Let’s learn when you’ll have to replace it, the building code it impacts, and how it impacts the price of a new roof. 

1. Roof sheathing may be replaced during a roof replacement

A roof replacement requires tearing off your old roof down to the sheathing before installing the new components and materials. Before installation can begin though, your roofing contractor will determine if your current roof sheathing can hold the weight of a new roof. 

If your roof sheathing's integrity is compromised or there are signs of rotting, the wood will need to be replaced. Most roof replacements require a few boards to be changed out. 

But if they find a lot of rotten boards, it may lead to a full re-deck. Unfortunately, your roofing contractor won’t know how much roof sheathing needs to be replaced until after they finish the tear off process.

(Section with replacement sheathing)

Just know that if your contractor finds your sheathing’s integrity to be sound, it can handle your new roof. So, you might not have to replace your sheathing if it’s in good enough shape.

However, not having to replace at least one board during your roof replacement is rare.

2. The building code that impacts roof sheathing

You just learned that rotten or damaged roof sheathing needs to be replaced before installation can begin. However, there’s actually a building code that specifies sheathing must be replaced in certain cases. 

Per R905.1 of the 2018 International Residential Code: roof coverings (roofing materials) shall be applied in accordance with applicable provisions of this section and the manufacturer’s installation instructions.

This code simply means your local roofing contractor must follow all installation instructions provided by the manufacturer of your roofing material. Because of this, plank sheathing that has more than an 1/8” gap between the planks must be replaced due to the manufacturer’s installation instructions before roofing materials can be nailed on. 

(Nail coming through gap in plank sheathing)

Failing to do so, will even void your material warranty from the manufacturer. Keep in mind that this is specific to plank sheathing. So, you won’t have to worry about this if you have sheet sheathing.

3. How roof sheathing impacts the cost of a new roof

Every roofing material and component installed on your roof impacts the cost. Having to replace roof sheathing is no different.

Unfortunately, the exact cost is hard to nail down due to fluctuating roof prices. However, wood prices have calmed down in 2022 compared to the year prior. 

While I can’t give exact prices or even a price range, I can give you an idea of how it impacts the cost of your new roof. It’s pretty simple, but the price increases as more sheathing gets replaced. 

So, a full re-deck is significantly more expensive than replacing a few rotten or broken boards. But remember, it’s impossible to see your roof’s sheathing until after the tear-off process. 

So, how roofing contractors decide to charge for roof sheathing differs. Every roofing contractor should have a line item in the estimate that specifies how much and what they’ll do if they find rotten sheathing. 

Some contractors automatically include a certain amount of replacement sheathing in their estimates. If this happens, you’ll pay for the sheathing whether the contractor uses them or not.

That’s why it’s always important to ask any potential roofing contractors how they’ll handle rotten sheathing when they go over your proposal with you.

Learn the rest of the roofing components included in your roof replacement

Now you know what roof sheathing is and what 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. 

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

Because of this, I wrote another article breaking down the main 9 roofing components that make up a residential roof system. 

Since 1990, the team at Bill Ragan Roofing has provided high-quality roofing services to thousands of homeowners in Nashville and surrounding Middle Tennessee areas. We take pride in our work and offer a lifetime craftsmanship warranty to back it up. 

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