Roof decking vs Roof Sheathing: What Are The Differences?

Roof decking vs Roof Sheathing: What Are The Differences?

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James
February 26, 2022
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Your roof is made up of important structures and components that ensure it remains strong, durable, and can tolerate the harsh weather in your region while blocking out moisture.

One of these structures that work hard to keep your roof in good condition is the roof decking.

What, exactly, is roof decking?

The roof decking is basically made up of wooden boards that are used to construct the frame of your roof.

Why is it important and how does it compare to roof sheathing?

Read on to find out what the difference is between decking and sheathing, and why ensuring that your roof decking is strong will increase the lifespan of your roof.  

What Does Roof Decking Actually Do? 

Roof decking vs Roof Sheathing: What Are The Differences?

Roof decking is basically the foundation of your roof. It is made up of the supporting roofing materials, such as steel, wood, and concrete, upon which the roof shingles or tiles are placed.

Roof decking also helps to seal your home against moisture and water damage, so you can see that it has to be strong enough to keep the entire roof structure solid and watertight.  

What Are The Different Types Of Decking? 

Decking comes in three main types. These are:

Plank decking

This used to be the primary type of decking that was used in roofs before plywood came about. It takes the form of rectangular, elongated wooden boards, and you can find them in two sizes: 1×6 or 1×8 boards. 

Sheet decking 

This type of decking is made up of flat sheets of wood, either made out of OSB (oriented strand board) or plywood. OSB is the most common type you’ll find and it is made up of wood strips that are compressed together to form a flat sheet that’s 7/16 inches in size.

Sheet decking is otherwise known as sheathing. As for plywood decking, it can be purchased in various thicknesses, and the one you choose will depend on the span of your roof’s rafters.

Tongue and groove 

This type of decking is usually found in houses that don’t have ceilings. It’s made up of 2×6 boards that have a tongue on one end, hence its name, and then it gets fitted into a groove located on the edge of another board to create a proper fit and seal. 

What Are The Three Types Of Roof Decking Material?

Roof decking vs Roof Sheathing: What Are The Differences?

Not to be confused with the different types of decking, you can also get roof decking in different materials. 

Concrete Decking

Concrete decking is basically a piece of concrete that seals off the top of the home. You can get this material in structural concrete and structural concrete composite.

  • Structural concrete. This is normal-weight concrete that can tolerate heavy loads. It’s usually insulated with the use of installation panels.
  • Structural concrete composite. This decking is an option when installing a level above the roof is a possibility in future. It is made up of a steel panel deck system that contains normal-weight concrete or structural lightweight concrete. 

Wood Decking 

If wood is chosen as the material for your roof decking, it comes in different forms.

  • Zip wood. This is durable and removes the need for roofing felt. It’s resistant to moisture, so it prevents leaks from forming in your roof.
  • FRT plywood. FRT (fire-retardant plywood) helps to prevent fire from spreading. However, it’s not always the ideal material to use because it can degrade before its time. 
  • CDX plywood. This is strong and durable because layers of wood are compressed into one. Since the wood grain varies from one layer to the next, this further boosts its durability. CDX can tolerate moisture and rain exposure, so it’s a great material for decking. 

Steel Decking

Steel is lightweight yet highly durable. It’s resistant to hail and other harsh weather elements.

Since steel can reflect heat more than other materials, it is ideal in hot climates, and it can also reduce your energy bill by decreasing how much heat enters your home. Steel also won’t warp or bend, so it’s resistant to various types of damage.  

So, Is Roof Decking The Same Thing As Roof Sheathing? 

Roof decking vs Roof Sheathing: What Are The Differences?

Although you might have heard about roof decking and roof sheathing, the truth is that both terms refer to the same thing! Although some roofing contractors might use one term over the other, they’re essentially referring to the same roofing material. 

How Much Does Roof Decking (Or Sheathing) Cost? 

Generally, roof decking comes as a regular piece of wood, such as plywood, that’s 4×8 feet in size and can range from a quarter-inch to ⅝-inch thickness. The thicker your plywood, the more expensive the cost of the sheathing will be.

On average, the price can vary from between $70 to $100 per plywood sheet. Note that a plywood sheet that’s 4×8 in size will cover approximately 32 square of the roof area.

The average roof measures 3,000 square feet, so you can see how the cost of decking could easily notch up a lot of expenses. 

Does Decking Need To Be Replaced When You Replace Your Roof? 

If you’re replacing your roof, such as by installing new shingles, you might wonder if your roof decking will also have to be replaced at the same time. The answer is not necessarily. It depends on the condition of your roof.

For example, if your shingles or roofing material have been damaged, this could have caused problems such as water damage in the decking. If this is the case, then it will make sense to replace your decking at the same time as your roof.

Bear in mind that the roofing contractor requires a solid foundation for the shingles to be installed, so the quality of your decking needs to be of a high standard. 

How To Look After Your Roof Decking 

Roof decking vs Roof Sheathing: What Are The Differences?

With all this talk about how important it is to ensure your roof decking is of a high quality, you might wonder if there’s anything you can do to keep your roof decking in good condition.

The first thing you can do as a homeowner is be aware of possible problems that can affect your decking. One of the most common is rot. This is caused by water penetrating the roof and reaching the decking. When this happens, you can’t repair the decking as it will need to be replaced instead.

However, you can inspect your roof for signs that your roof decking is at risk of damage and rotting. Since decking sits underneath the roof shingles to protect the house against moisture, if the shingles are broken or loose then they should be repaired to prevent your decking from getting damaged.

Inspect your roof’s shingles regularly so that you can repair loose, broken shingles as soon as you notice them to prevent them from causing bigger problems to your roofing structure. This will also ensure that your roof looks good. 

Other ways in which you can keep your roof decking in excellent condition is to follow these tips:

  1. Keep your gutters clean. Remove debris and snow from them regularly to prevent blockages that can prevent the proper flow of water. 
  2. Avoid leaving snow to accumulate on your roof. If there’s more than 12 inches of snow on your roof, you need to remove it, such as with the use of a roof rake. If left to sit on the roof, it can cause damage from the weight and via water damage. 
  3. Maintain good ventilation for your attic. This prevents your roof from being exposed to ice dams in the winter. How it does this is by preventing snow from melting underneath the roof and accumulating there, where it will damage the roof decking. Shingles and roof decking can warp and curl when the attic becomes too hot, so ensuring the attic is properly ventilated will also keep the roof temperature at a healthy level. 
  4. Remove debris regularly. You should clean your roof of debris regularly so that it can’t accumulate and become a problem. If wet leaves, moss, and other debris accumulate, this can trap moisture that will seep underneath the roof shingles, then penetrate the underlayment before reaching the roof deck where it can cause damage such as rotting. If your roof is susceptible to moss growth, you can prevent this problem by installing zinc edges on the roof. The metal will block the growth of algae and moss. 
  5. Ensure you’ve got the right underlayment. The roof’s underlayment is placed underneath the shingles and above the decking. It’s supposed to be an extra level of protection for the decking, so you have to ensure your roof has the right one to meet its needs. If you don’t have the right underlayment, this will expose your decking to damaging conditions. Check what underlayment is required for your specific roofing material when your roof gets installed. 

What Do Building Codes Say About Roof Decking? 

Roof decking vs Roof Sheathing: What Are The Differences?

There are some roofing code requirements homeowners should know when it comes to decking or sheathing. Let’s explore them. 

  • Your sheathing should be at least ⅜-inches thick. There is no upper limit for the thickness, however. It will depend on how far your trusses or rafters are spaced. This will vary from one roof to the next.
  • Building code requirements don’t make specifications for different types of roof decking. This is because the OSB or plywood you purchase for your roof will be labelled to inform you of the loads and maximum spans which are allowed for that type of substrate. This therefore makes it easier to choose the right decking for your home.

Can You Install New Roof Decking Over Old Decking? 

If your current decking is a bit damaged or you want to reinforce it, you might wonder if you can install new decking over it. This is not recommended. 

The new wood, or other decking material, would have to be nailed to the roof trusses or rafters. If the old decking is still present, this would make it difficult to find the rafters so that nails can be properly placed and secured.

Some nails won’t get attached properly, so you might end up fastening the new decking to the old one, instead of to the rafters or trusses. This means that your new decking won’t be properly attached to the roof surface, which will make it susceptible to damage, such as in the form of wind.

In addition to the above, it’s important to note that installing sheathing over the existing one will increase the roof’s weight. It therefore makes more sense to remove the decking, especially if it’s damaged, and replace it with new materials. 

Conclusion 

If you’ve ever heard the terms roof decking and roof sheathing, you might have wondered if you can use them interchangeably or if they refer to different roofing structures or materials.

You can use them interchangeably because they’re two words for the same roof material!

In this article, we’ve explored what you need to know about roof decking or sheathing, its different types, and how to keep it in excellent condition so that your roof structure doesn’t fail you, causing you lots of headaches and high costs to repair or replace your roof. 

Sources:

James

James Weldon is a professional roofing contractor with many years of experience on the job. He does not only handle large projects and provide excellent services for his company’s many clients; James Weldon also dedicates his spare time to teaching others useful tricks of the trade. Using BuildCampus as an avenue to reach many roofers and aspiring roofing contractors, James Weldon continues to provide high-quality educational posts and buying recommendations for anyone who visits the website.