The roof is arguably the most important component of a house. After all, it is what protects everything inside from the elements.


Whatever material your roof is made of is ultimately held up by the roof deck (also known as roof sheathing), making it one of the most critical parts of any building.

What Even is Roof Sheathing?

Roof sheathing, also called decking or substrate, is a layer of wood paneling that supports the shingles, tiles or whatever roofing materials are on your roof. The sheathing is fastened to the roof’s joists and trusses, and then the shingles are nailed down to the sheathing. Sheathing supports the rest of the roof and acts as a last line of protection from the elements. Because sheathing is a wooden product, it is subject to water damage and dry rot if kept in a humid environment. Replacing the sheathing on your roof can get expensive if there is extensive damage, so make sure to inspect your attic regularly to make sure things are dry and sound. 

If you have a tile or wood shake roof and are looking to replace it, you may have to get new plywood installed if you don’t already have it. Oftentimes on those roof types there is a type of sheathing called “skip-sheathing” which many roofers will not install on top of.

What Does Roof Sheathing Do?

1. Supports shingles/tiles

Sheathing makes up the base of your roof. It literally holds up the shingles or tiles or whatever material your roof is made out of. These materials are fastened to the sheathing with either nails, staples, or screws.

2. Prevent leaks

Sheathing prevents leaks by providing a smooth, solid surface that holds up the waterproof underlayment that protects against moisture penetration. 

3. Prevents wind damage and blow-off

A good solid roof deck will act as a steadfast anchor to secure your roof during storms and other high wind events.

 4. Strengthens roof structure

The roof deck spreads the load of the roofing material evenly over the roof joists. The deck makes it easy to walk on your roof without fear of falling through the roof.

5. Makes future roof work easier

Having a solid roof deck makes it much easier for contractors to replace your roof in the future or install other equipment on your roof such as solar panels.

Man installs plywood on roof frame

What is Roof Sheathing Made From?

Roof sheathing can be made of a number of different materials, but most commonly it is 7/16” OSB plywood. This is a standard roofing and construction material that can be found all over the country.

However, older roofs often have a different style of sheathing constructed from long wooden planks that are nailed down across the roof joists.

This is an example of board or plank sheathing, which is simply when boards are fastened down on top of the roof joists to create a solid deck. This style of sheathing does not leave large gaps in between the boards. A new roof can be installed on this style of sheathing, assuming that the boards are still structurally sound and there are no large gaps between them.

This style is called “skip-sheathing”. Notice the “skip” or gap in between each board. This gap increases ventilation and decreases material costs, but does not provide a solid surface to attach materials like asphalt shingles, and is no longer really used. A “solid deck” of OSB plywood must be installed over skip-sheathing when replacing a roof.

When Do You Need to Replace Roof Sheathing?

  1. If you are experiencing leaking from your roof or you can see moisture or water damage on your sheathing. This is a strong sign that the structural integrity of your roof deck is compromised and some or all of the sheathing must be replaced.

2. If you see the wood is rotted or there is fungal growth on the sheathing or roof structure. Dry rot and mold can cause serious damage to wooden structures and must be removed and replaced with new materials when it is encountered.

3. If you have skip-sheathing. If you are replacing your roof or planning on installing solar panels, it is recommended that you replace any skip-sheathing with a solid deck of 7/16” OSB or plywood.

4. If your roof is sagging. A sagging roof can be a symptom of sheathing that has lost its structural integrity. If your roof is beginning to sag, it is a good idea to take a look in the attic and see if there is excess moisture or rotting in the sheathing or roof joists.

If you have a roof with any of these issues, it is recommended that you speak with a roofing professional to discuss your options and to see if replacing your roof is necessary. As a preliminary step, we recommend inspecting your attic annually to assess the condition of the sheathing of your roof. To do so, go into your attic with a flashlight and take a look at the plywood boards and roof joists for any damage or moisture. Unfortunately, it is rarely possible to replace or repair roof sheathing without destroying the roof on top of it. For this reason, we recommend having a full roof replacement when sheathing needs to be done. That way you will not have to worry about any issues with your roof for decades to come.


To see how much it would cost to replace your roof, visit to receive free estimates from a number of installers in your area.