Roof Sheathing vs. Roof Decking: 7 Things Homeowners Should Know

Kenneth Wilson

Whenever I discuss roof sheathing or decking, it's prevalent to witness visible confusion among homeowners.

Here's a couple of questions I usually hear:

  1. 1
    What is roof sheathing or decking?
  2. 2
    Do they refer to the same thing?
  3. 3
    Is roof sheathing different from decking?

And while I understand it does get a little confusing at some point, let's make one thing clear first– roof sheathing and decking are practically the same things.

Different roofing contractors just use these terms almost interchangeably, mainly depending on personal preference. Keep in mind that plenty of technical terms are commonly used in the roofing industry.

Roof decking or sheathing refers to the roof foundation. It can be concrete, steel, or wooden material on which the roof shingles are placed. That said, it acts as a seal for your home. This protective layer protects the house from leaks, water damage, and other related issues.

Let's find out the critical role of roof decks in your home's safety and structural integrity.

Difference Between Roof Sheathing and Roof Decking

The terms roof decking and sheathing are often used interchangeably– but one thing to keep in mind is how these terms refer to a similar process (crucial roofing element).

You might notice some contractors prefer using one term over the other, but there's no big difference between the two. With that said, we'll refer to roof decking and sheathing synonymously in this article.

Generally, decking or sheathing refers to the boards that comprise the foundation of your roofing systems, such as beams, joists, and trusses. AKA, roof sheathing refers to where the shingles and other roof components are installed.

In the USA, roof sheathing is generally made of wood, OSB (Oriented Strand Board), or Plywood. OSB material is cost-effective, easy to work with, and highly durable to resist bending. While plywood will cost you more, it is more robust and better suited for heavy roof covers (clay, concrete, or slate).

What is Roof Sheathing or Decking?

Commonly, roof sheathing or decking is made of OSB or plywood. Homeowners working with a limited budget can benefit from the lower price of OSB. Meanwhile, plywood is more durable– but this comes with an increased price.

Most roofers simply prefer OSB unless the homes have heavy materials such as concrete or slate roofing materials. In such cases, you may be better off choosing plywood instead.

The sheathing is designed to strengthen the roof. Picture out a sturdy support system that can hold the rest of the roof components in place. (Related: Five Things Homeowners Should Know About Roof Sheathing Before Getting Their Roofs Replaced)

Variations in Roof Sheathing

The sheathing is available in various thicknesses. The material chosen by your contractor will depend on different factors.

For steeper roofs, thin/light sheathing is ideal to avoid any excessive weight. The same goes for flat roofs or roofs with lower slopes.

Pre-Roof Sheathing

One thing you may notice in older homes is the lack of sheathing. Instead, they have board layers placed under the shingles– which were at an increased risk of leaks.

Ideally, opt to give your home proper roof sheathing to decrease the risk of leaks and improve the condition of your roofing system. Not to mention, it also keeps the shingles nailed to hold them in place.

Different Types of Roof Decking

Nowadays, you can choose from different materials for roof sheathing/decking. Some of these types may best suit specific residential roofing systems.

Refer to a quick overview below to make an informed decision for your needs.

  • Oriented Strand Board (OSB) - Considerably the most common roof decking material, OSB is highly durable, affordable, and accessible. This material is composed of wood layers bonded together with adhesive, making it appear like plywood. Thanks to its lightweight nature, it adds less stress to your roof.
  • Plywood - A construction-grade plywood material is another popular material for roof sheathing. Installing this sheathing option has the same process as OSB, such as standard spacing for contraction or thermal expansion. If you're looking for a solid and durable choice– this one's for you. Plywood for roof decking is commonly available in 4x8 sheets.
  • Tongue and groove - This decking material is often available in 2x6 boards. It is called tongue and groove to refer to its varying ends, which lock into each other. Tongue and groove are commonly used on roofs without a ceiling, and the boards can be visually appealing when seen from indoors.
  • Plank sheathing - Although this material is not as popular nowadays, it's still commonly used for specific roof types (including wood shakes).

Benefits of Roof Sheathing or Decking

So, why should you consider roof sheathing? Here are some advantages to keep in mind.

Stop Leaks

Asphalt shingles are now marketed to be weather-proof, but roof sheathing adds another protective layer to your home roof system. It also prolongs the lifespan of your roof and protects your interiors from water damage.

Previously, traditional roofs weren’t made with sheathing. Since these roofs are likely prone to leaks, roof decking grew in popularity to add a protective barrier between the shingles and boards in your home roofing.

Improves Roof Strength and Support

Sheathing allows the weight to be evenly distributed across the roof. You'd be surprised at how heavy shingles are– so it's ideal to have this added weight distributed evenly across the entire surface.

It is commonly affixed to the joints and trusses in the roof, AKA the most substantial beams, to protect the roof from damage (sag or bow) in the event of heavy snow or rainfalls.  Homeowners using asphalt shingles can benefit from this aspect enormously.

Fire Proofing

Another benefit to roof decking is its fire prevention properties. It's not 100% fireproof, but most sheathing materials are treated with fire-retardant properties.

It protects the roof or attic from potential fires, as it is difficult to spread around.

Roof Decking does not Require Replacement

Some of you might be wondering: am I required to replace my roof sheathing if I have my shingles replaced?

The answer varies on a case-to-case basis, depending on factors such as your home’s current condition and roof age. Nonetheless, many homeowners find it convenient to opt for a roof sheathing replacement once they replace the other parts of the roof.

A local professional roofing company can help you assess the current roof decking condition and give valuable insights before deciding.

Some Telling Signs of Damage

Fortunately, it's easy to tell if a roof needs immediate repair. Some telling signs are faded or warped shingles, as well as missing ones. However, determining the roof sheathing condition may be a bit more challenging to do.

For your reference, here are some of the most common warning signs:

  • Leaks are becoming more frequent
  • Sagging ceilings
  • Visible water stains
  • Mold or mildew

These basic warning signs suggest possible roof damage. As much as possible, contact a local roofing professional immediately to assess the damage and do repairs at once. If your roof sheathing is years-old or damaged, consider a replacement as soon as you can. Always keep in mind that decking is a crucial component of your home’s roofing system.

  • There’s visible water damage: It will be bad for any part of your roof if it catches water damage. You will know that it is time to replace it when visible leaks, water stains, or puddles appear in your ceiling. Sheathing water damage is terrible as it can affect your roof's structure. Replacing the damaged boards as soon as possible is the best thing you can do.
  • There’s rot: It is high time for a replacement if you see some rotting parts of your roof's sheathing. Often, water damage is the cause of rotting sheathing, but it can be less noticeable if there are no visible leaks.
  • Sagging ceiling or roofline: Sagging in your ceiling or roofline is the best way to identify potential roof sheathing damage. The sheathing might be to blame if you notice that some areas of your roofing appear closer to you than others.

Why Should I Invest in New Decking?

Even in cases where the existing roof decking doesn't need urgent replacement, there are plenty of reasons you can benefit from this investment.

First, it dramatically improves the home's structural integrity. It is an excellent value to consider if your property is located in hurricane-prone areas. The stronger the home's structure is, the better.

Investing in new roof decking allows you to choose a particular decking material best suited for your home needs. It's common for homeowners to upgrade their old wooden decks to metal, which is a more energy-efficient choice. It may require you to shell out on high upfront costs– but the savings from the reduced energy bills and insurance discounts can help settle the payment.

It's ideal to have a solid, firm grasp on the different elements of your roof. Doing so helps you make an informed decision in terms of necessary roof repairs and maintenance activities.

Bottom line, consider roof sheathing or decking to be an essential part of a residential roofing system. It holds up the shingles, protects the roof from foreign elements, and distributes the weight across the roof evenly.

Kenneth Wilson
November 26, 2021
Contractor Tips, Roofing

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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