What’s the first thing you see when looking up at your roof? Many people believe that a roofing system comprises shingles or tiles. However, there’s much that you cannot see under these materials.

Every roof system needs a foundation to sit on. This is where roof sheathing comes in.

However, many homeowners question it: What does “roof sheathing” mean? Does it need to be replaced every once in a while? Are there different types?

brown brush on wooden board

Fortunately, here’s all the information you need. Read on to find all the answers to these questions and more!

What Is Roof Sheathing?

Also known as roof decking, “roof sheathing” describes the wooden boards forming the system’s framing, supporting hanging shingles, shakes, or tiles.

When installing roofs on residential buildings, technicians must leave a 16″ and 24″ spacing between rafters or trusses. As a result, these structures have large and open gaps.

To close off those gaps, you need a protective covering. That’s the roof sheathing.

Experts must install your shingles and other roofing materials or elements on these wooden boards. This covering protects the system’s internal components to keep the structure intact.

Sheathing boards also protect properties against leaks. Therefore, it’s crucial for the system’s longevity. In addition, this structure distributes the load evenly in case of heavy rainfall or snow, preventing your roof from sagging.

Types Of Roof Sheathing

These boards come in different types, which vary depending on the roof sheathing materials and the layout. However, these are the most common:

  • Oriented Strand Board (OSB)
  • Plywood, particularly CDX
  • Concrete
  • Wooden planks
  • Skip sheathing

Find more information about each roof sheathing material here!

Oriented Strand Board (OSB) Roof Sheathing

This material has been synthetically manufactured with different wood fragments, which are held together by special adhesives to create strong bonds between each one.

OSB boards are thick, sturdy, and less prone to swelling or warping over time. They have a uniform finish and are less expensive than other alternatives.


  • Affordable
  • Less vulnerability to swelling or warping over time
  • Thick panels


  • Presence of formaldehyde
  • Vulnerable to water damage

Plywood Roof Sheathing

Like OSB, plywood structures have different wooden layers bonded with special adhesives. It’s another popular option for roof decking.

Since it’s quite dense, plywood layers form a thick board that favors nailing. They also prevent water from reaching the core layers.

Thanks to this layering, these boards don’t shrink or warp. As a result, this roofing material lasts for a long time.

wooden roof sheathing


  • Available in multiple sizes, shapes, and finishes
  • No swelling when exposed to water
  • Lightweight


  • Expensive
  • Smaller panels
  • High maintenance

Concrete Roof Sheathing

Concrete sheathing is one of the best options when roof systems require high strength and sufficient support. It’s uniform and sturdy. In addition, this roofing material is more continuous than wood, so it prevents water leaks.

If you choose this option, technicians must pour concrete into prefabricated boards in several sets. After this step, they must place metal reinforcement.

It’s one of the most popular roof sheathing materials for green projects, as it replaces wood and helps reduce tree felling. However, concrete still has its carbon footprint.

Concrete can withstand strong winds, lasts for years, and doesn’t require extensive maintenance.


  • Fire resistance
  • Long-lasting materials
  • Lightweight
  • Paintable
  • High strength
  • Protection against rots and insects

Skip Roof Sheathing

If professionals must install skip sheathing, they place wooden planks, leaving a space between each one to allow air to pass through to dry out structures exposed to moisture.

While this roof sheathing material and technique are effective, the structure degrades over time. Therefore, you may need to make another investment to re-sheet the system.

However, many new materials have built-in small pores that promote air circulation, outperforming skip sheathing.


  • Moisture resistance
  • Less material cost
  • High durability


  • Expensive boards
  • Infectivity in areas with windy rains or significant rainfall

Wooden Boards Roof Sheathing

Although people began using wooden roof sheathing in the 20th century, wooden boards made from the bark of local hardwoods are quite popular.

Technicians cut wooden planks into the required shape and install them over the rafters. After this step, they add shakes and shingles to the sheathing.

person holding nailing gun sitting on wooden roof deck

People prefer asphalt shingles since these shakes eventually fall off and require replacement. Also, they’re more durable and cheaper. However, this roofing material requires a more solid support base that plain wooden boards don’t provide.

That’s why professionals replaced wooden board sheathing with new and improved options, such as OSB and plywood when installing asphalt shingle roofs.


  • Great insulation
  • Robust structure


  • Difficult to install
  • No warping over time

5 Things You Should Know About Roof Sheathing

Besides the types of roof sheathing and the definition, you should also know the following five things about this process:

Roof Sheathing Replacement

If you’re considering a roof replacement, you may also need to replace the roof sheathing, as this process involves tearing down the old structure to install the new components.

However, a roofing contractor must inspect the system to determine if the current sheathing can support the new roof materials.

Also, you may need to replace these roof coverings if the sheathing has degraded over time.

Roof Sheathing and Costs

You should consider sheathing to determine how much money you need to install a new roof. Remember that each material technicians use can impact the final cost.

Prices usually vary depending on the materials—however, the more sheathing that needs to be replaced, the higher the cost.

In other words, you might need more money to replace the entire roof deck, for example. However, roof decks that only need minor fixes would be cheaper.

Additionally, each roofing contractor has their criteria for how much they’ll charge for roof sheathing replacement.

Building Code and Roof Sheathing

Several signs show you should replace your roof sheathing before installing a new roof, such as a rotten or damaged structure.

However, a building code can determine when this structure must be replaced. Therefore, you should check the applicable local provisions to see if installing a new structure is time.

According to R905.1 of the 2018 International Residential Code, roof coverings must be applied according to the installation instructions provided by the manufacturer. If there’s a ⅛” gap between the planks, you’ll probably need to replace the sheathing before the installation begins.

Roof Sheathing Dimensions

To determine the roof sheathing thickness, consider the roof’s steepness, the spacing between the rafters, and the snow load the structure must bear.

Most roof sheathing panels come in 4″x8″ rectangular blocks. The thickness lies between ½” and ⅝,” but the recommended minimum thickness for plywood sheathing is ⅜.”

roofing specialist installing new roof

Sheathing for Metal Roofs

A metal roof also requires sheathing, as this component stabilizes the structure and prevents it from bending.

Also, on metal roofs, the sheathing allows the load to be uniform throughout the entire structure instead of concentrating in one place. This component also provides extra protection from the sun’s radiation during the summer.

Final Thoughts

Roof sheathing makes roofing systems sturdy, resilient, and long-lasting. In addition, they provide support for shingles, shakes, and tiles. It’s the strongest layer of the structure, so it’s one of the most important components.

If you want to install your roof sheathing or know if you should replace the structure, don’t hesitate to contact a professional roofer!


CDX is a popular type of plywood for roof sheathing, but is it better than OSB? Both materials provide a high level of protection. However, you must choose the one that best suits your roof.

OSB is more water-resistant than CDX since this material absorbs and loses liquids easily.

Also, CDX is more expensive than OSB. Therefore, if you choose this material, you might need more money for your roof replacement or installation process.

However, if you have doubts about the best option for your roofing system, ask an expert for help!

Yes, it is! Roof sheathing fulfills different purposes and serves multiple functions, such as providing protection against water, preventing leaks, wind damage, or blow-off, and withstanding other harsh conditions. Furthermore, this component makes up the base that supports the roof materials.

It depends on the conditions of the roof deck. If it’s rotten or damaged, people must replace the roof sheathing.

As mentioned, local provisions and regulations may also define when people should replace this component or when a new installation might be the best option.

Ideally, homeowners should speak with a roofing contractor to inspect the roofing system and determine the best course of action.

The roof sheathing degrades over time. Therefore, you may need to replace it if it’s rotten or damaged.

Sometimes a roof repair is enough. However, if you notice the following warning signs, you should call a professional who will inspect the structure and determine if a replacement is more convenient:

  • Cracks: If the roof sheathing develops cracks due to poor load distribution, you may need to replace the entire structure. This is also necessary when a tree falls on the roofing system and breaks this component or when continuous moisture causes damage.
  • Fungal and mold growth: If there’s fungi or fungal growth on the roof sheathing, you should also consider a replacement.
  • Bowing or bulging: The decking may sink or swell up due to moisture. These may be signs that the structure is rotten.
  • Water damage: Prolonged exposure to water or humidity can also cause the sheathing to weaken and the materials to start to fall off.
  • Blackened spots: If you notice black spots on your roof and the material gives in easily, you should immediately call a professional. They often suggest that the structure is rotten or compromised.
  • Sagging: It’s one of the biggest signs that the roof needs to be replaced. Besides being unattractive, it’s dangerous.
  • Holes: Since they allow water to enter the structure, you should request an inspection to determine if you need a replacement if you notice holes in your roof.