Get a Free Inspection

The Parts of a Roof: What is a Roof Deck and What is its Purpose?

what is roof deck under the shingles

If you are fixing your roof or hiring a roofing contractor to install a new roof, you may have heard the term roof deck. Knowing the various components of a roof and how they work together will ensure you have the best roofing solution possible. 

So, what is a roof deck?

It’s important to get informed before scheduling a new roof installation, so we’ve put together a guide to help.

Roof sheathing is another name for it. A roof deck is installed under your roofing materials, such as shingles or tiles. It is a crucial part that helps support the materials with installation on top of the building’s trusses over the rafters. 

This guide covers everything you need to know about roof decking, its purpose, whether roof decking should be replaced, and other vital elements. 

What Is Roof Deck?

what is roof deck and its purpose

Many homeowners aren’t aware of the multiple components that help make up their roofing system. The roof deck acts like the base or foundation for your roofing materials.

To understand where a roof deck fits into your structure, this list describes each part in the relevant order to others that make up your roofing system: 

  • Building frame, joists, and trusses
  • Vapor barrier 
  • Roof deck
  • Insulation
  • Waterproof layer 
  • Roofing materials, like shingles or tiles

Roof decking affect ventilation through the attic space of a home. Poor ventilation can create condensation, causing mold, mildew, and rotting wood planks, beams, and drywall. 

Once mold and rot enter your attic, it’s best to call a roofing contractor for an entire roof replacement. 

If you don’t address the moisture problem, your attic space can cause wood rot in your rafters, resulting in rotten decking, where the shingles will not remain fixed to the roof decking.

Types of Roof Decking 

A roof deck can be of various materials, depending on the type of roof you want and need for your region and your budget. The new roof deck you choose may be affected by current wood prices in your area and what you will use to protect your home outside. For example, the decking you will use for asphalt shingles will differ from roofs that use wood shingles or ceramic tiles.

A common type of roof decking can use: 

  • Metal
  • Plywood
  • Plank sheathing 
  • Oriented Strand Board (OSB)
  • Tongue and Groove 


what is roof deck using plywood

Sheets of plywood are quite commonly used as a roof decking option. It can be more costly than OSB decking, especially if you are considering using thicker plywood decking materials.

This roof decking option is available in several sizes for your home, including:

  • ⅜”
  • ½”
  • ⅝”
  • ¾

Another option in this category is CDX plywood. This product uses thin pieces of plywood bonded with adhesive, creating a strong, more water-resistant decking option. 

Plank Sheathing 

Not many homeowners find plank sheathing an ideal choice to replace their roofing system unless they use wood-shake roofing products. 

This roof deck type consists of plank boards that are installed approximately 1 ½” apart from each other. You can find them in 1×6 or 1×8 measurements to suit various needs. 

Oriented Strand Board (OSB) 

OSB is the most common type of installed wood roof decking in homes. Its durability and affordability make it a terrific material. 

It uses compressed layers of wood strands using adhesive products in an orientated overlapping pattern and measures 7/16”. The structure makes it stronger and ideal to use for a roof deck. 

Tongue and Groove 

This roof decking option is more common in homes where it will be visible inside because of its aesthetic appeal. 

Tongue and groove decking for roofs uses 2×6 boards. Each has a tongue on one end and a groove on the opposite. This way, the boards lock together easily, creating the new roof decking. 

The Purpose of a Roof Deck 

Functional roof decking will support the roofing materials, like shingles or metal, ensure the solidarity of the home, and protect the structure from harmful weather conditions. 

It cannot do its job correctly if it has rotting roof deck sections or is compromised due to cracks, holes, or other damage. If that’s the case, it might need to be replaced.

Does Your Home Need a Full Roof Replacement or Just New Roofing Materials? 

what is roof deck roof replacement

Sometimes a roof replacement job will include a complete roof decking installation, but that isn’t always the case. 

Depending on the condition of your existing roof deck, some common roof repairs can be done without a professional roofing contractor having to replace the entire decking.   

If you have serious concerns about your roofing needs, your local roofing contractor can provide more information. They will explain what a new roof entails or confirm if your roof’s decking needs replacement. 

What Would Cause Your Roof Decking to be Replaced? 

An expert roofing contractor can determine if your shingles need repair, if you need your roof replaced, or if you’d benefit from a full roof decking solution. 

Here are some typical reasons you need to replace your roof decking. 

  • Old, broken, or worn-out shingles allowing water to reach the roof decking
  • Inadequate roof ventilation causing moisture buildup
  • Improperly installed ice dams or roof flashing
  • Clogged roof gutters or downspouts that force water into the roof system

Regular roof maintenance and care can ensure your roof decking stays functional and any minor roof repairs are handled. That way, you won’t have to worry about issues evolving into bigger problems and decking needing to be replaced.

Some typical signs that can indicate a roof decking issue in your home are: 

  • Mold or mildew smells in the home
  • Visible water stains inside the home 
  • Water or moisture on the ceilings or walls
  • High energy costs 
  • Rotting trusses or wooden beams in the attic
  • Appearance of insects 

Wrapping Up

So what is a roof deck? Roof decking is just part of your entire roof on a home. However, without it, your structure cannot protect you and your belongings from rain, snow, and other elements. Although several options exist for decking products, most common roofs with shingles will use standard OSB or plywood choices. 

Talk to an expert roofing contractor if you have any concerns about your roof deck or want to know if it needs to be replaced. Getting a professional assessment early on can prevent more costly problems later. 

Share This Article:

Recent Posts

Check Out the Latest From Our Blog

Bay Valley Roofing

Protecting your home and the lives you create in IT

Get a Free Inspection