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Are Roof Decking and Roof Sheathing the Same Thing? (4 Things to Know)

July 12th, 2021 | 6 min. read

Are Roof Decking and Roof Sheathing the Same Thing? (4 Things to Know)

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There are a lot of technical terms used in the roofing industry. But there are also different variations of these terms depending on how the contractor learned about roofing. 

This isn’t a bad thing. It just gets a little confusing sometimes when talking to different roofing contractors. 

A couple of these terms are “roof decking” and “roof sheathing”. Homeowners ask, “Are they the same thing?” “Do they each do something different?” “Does your roof need one or the other?” 

At Bill Ragan Roofing, educating you and giving you the information you need before making such a sizable investment is our main job. The last thing you need during a stressful time is to be confused by the terminology. 

Here, you’ll learn if roof decking and roof sheathing are the same thing. You’ll also learn 4 things about them to give you a deeper understanding of this crucial roofing material. 

Are roof decking and roof sheathing the same thing?

While some roofing contractors use different terminology, roof decking and roof sheathing are the same thing. But now that you know they’re the same thing, what is roof decking (roof sheathing)?

Roof decking (or roof sheathing) is the wooden boards that make up the foundation of your entire roof system. I like to say foundation because it’s what your shingles and the rest of your roofing components are installed on. 

roof decking and roof sheathing

Roof decking is one of the most important pieces of your roof system. Without it, your roof literally has nothing to stand on.    

4 things you need to know about roof decking (roof sheathing)

Now that you know what roof decking is, you’re ready to learn some important things about it. You need to know about the types of roof decking, the cost, and more.  

1. The two types of roof decking

There are two different types of wooden boards used on your roof: plank decking and sheet decking.

Plank decking was the main type of decking used before the invention of plywood. This type of decking is made up of elongated and rectangular wooden boards that come in two different sizes, 1x6 or 1x8. 

plank decking

While not as common as today, you’ll still find plank decking on older homes. But if your plank decking has a wider gap than is allowed per code (more on that later), it’ll have to be replaced. 

Sheet decking (or sheathing) is exactly what it sounds like, flat sheets of wood. There are two different types of sheet decking: plywood and OSB. 

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.

osb roof decking

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. 

plywood roof decking

Both types of sheet decking are great options, but which one you get depends on your budget and, most importantly, the availability of the wood.

2. You might have to replace your roof decking during a roof replacement

When you get a roof replacement, you might have to replace your decking. If any of your roof decking’s integrity is compromised or there are signs of rotting, the wood will need to be replaced.

rotten roof decking

Usually, there are going to be a few boards that have to be changed out. But your roofing contractor won’t know how much of your roof decking needs to be replaced until after they finish tearing off your old roof.

If they find rotten boards, your roofing contractor has to replace the decking before they can begin installing your roofing components. However, if your contractor finds your decking’s integrity to be sound, then it can handle your new asphalt roof. 

3. The code that has to do with roof decking

I mentioned above the reason your roof decking would need to be replaced. But there’s actually a building code that says it has to be replaced if the integrity of the wood is compromised. 

According to code R905.2.1 of the 2018 International Residential Code: asphalt shingles shall be fastened to solidly sheathed decks. This code means that your roof decking (roof sheathing) must be able to withstand and hold your new roof when it’s installed. 

If there’s any rotten decking or if the decking can’t handle the new roofing materials, it must be replaced before your roof is installed according to codes. There’s also a code that your roofing contractor has to follow the shingle manufacturer’s installation instructions. 

As of 2021, if any of your plank decking has more than an 1/8” between the planks, your roof decking has to be replaced per the manufacturer’s installation instructions before roofing materials can be nailed on.

plank roof decking

Be aware, some roofing contractors lower their prices by skipping this to undercut the competition. 

When meeting with your roofing contractor, always ask them (if they haven’t done it already) to check your roof decking’s integrity. 

4. The cost of roof decking

The price of wood in your area fluctuates weekly. So, it’s hard to give a price on roof decking. 

Unfortunately, in 2021, wood prices are through the roof, which adds a pretty big expense to your roof investment if a lot has to be replaced. While I can’t give exact prices or even price range, I can at least give you an idea of which type of decking is more expensive. 

For example, plank decking is priced out per linear foot, while sheet decking is priced out per sheet. After factoring in labor and materials, plank decking usually costs about three times more per square foot than sheet decking costs. 

So if you have plank decking and a lot of it needs to be replaced, it's actually cheaper to go over the top of the existing plant decking with OSB 7/16” or 3/8” CDX plywood. However, you won’t know the cost of your roof decking until your roofing contractor determines the type and how much needs to be replaced. 

The other roofing materials you need to know about

After reading this, you better understand roof decking, the types, the cost, and more. However, roof decking is just one of the important roofing materials that make up your roof system. 

Knowing the rest of the materials helps you understand what exactly you’re paying for when investing in a new roof. That’s why you and every other homeowner needs to learn the 9 roofing materials that make up your roof replacement. 

Since 1990, the team at Bill Ragan Roofing has helped homeowners like you in the Nashville area with all of their roofing needs. Whether it’s to repair your roof leak or to give you a beautiful new roof, you can count on us to do it with the attention to detail and expertise the project requires. 

Check out 9 Materials Included With Your Roof Replacement to learn what exactly you’re paying for when getting a new roof.

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