Skip to Content

When To Replace Roof Sheathing And What Does It Do

When To Replace Roof Sheathing And What Does It Do

Many homeowners are faced with the dilemma of whether or not they need to replace their roof sheathing.

This is a tough question because there are so many variables that go into it. If you have any doubts about your roof, then you should call a qualified home inspector to help answer this question for you!

When to replace roof sheathing and what it does can be answered in many ways.

While any time you replace roof sheathing could be the answer, there are some instances worth noting that would signal a need to look into replacement sooner than normal.

Also, knowing what your roof sheathing is made up of and how long its expected lifespan is along with typical installation practices will help you understand when to replace roof sheathing and what it do.

Why Replace Roof Sheathing?

According to Roofing for Pros, each type of roof sheathing has its own set of lifespan characteristics.

For instance, plywood lasts anywhere from 15-40 years, while asphalt shingles can last up to 20 years depending on the quality of the shingle.

Knowing what type of sheathing you have on your roof is step one in understanding when to replace roof sheathing and what it do.

Other factors that affect how long your roof sheathing will last are any kind of material defects, how high off the ground you are (elevation is especially an issue in colder climates where ice dams are more common), wind, sunlight, temperature changes and whether you have birds living on it.

These factors can lead to premature deterioration including rotting, delaminating, warping and cracking that indicate your roof sheathing needs to be replaced.

What Is Roof Sheathing?

Roof sheathing is the material that forms the base of your roof.

On a wooden framed home, it is the layer of plywood that sits on top of your rafters or trusses and helps support your shingles and other weather-proofing material such as underlayment.

While there are different types of materials used to sheath roofs, at least one type of material must be used.

What Is Roof Sheathing Used For?

As the base of your roof, roof sheathing is designed to support all other parts of your roof and keep it waterproofed.

Its main responsibility is to maintain a barrier between your shingles and the outside, preventing water from entering your home or building and causing extensive damage.

Is It Necessary to Do Roof Sheathing?

When it comes to construction or repairs, the roof sheathing is an essential component that cannot be neglected.

If your house was built before the mid-1970s, chances are you have wooden roof sheathing over your rafters which will need to be replaced at some point.

The roof sheathing is the structural layer that forms the base for any other roofing material; this could be wood, metal, or rolled roofing materials like asphalt and modified bitumen.

The roof sheathing also provides structural support for lumber and trusses, and acts as a base for an application of ventilation and insulation.

What Is The Most Common Type Of Roof Sheathing?

The most common type of roof sheathing is plywood, but there are many other options including felt paper, oriented strand board (OSB), particleboard and wood boards such as cedar, pine or redwood.

During construction, it is important to use roof sheathing that protects against fire, insects and rot.

Different Types Of Roof Sheathing

  • Felt paper – This material has a natural oiling effect on exterior walls which provides a measure of protection from moisture.
    • It also condenses water vapor that rises into the air from inside your home before it can condense and seep into your ceiling or walls.
  • Cedar, redwood and pine – These roof sheathing materials are naturally resistant to fire, insects and rot.
    • They also provide thermal insulation which can keep your home cooler during summer months.
  • OSB – Oriented strand board is manufactured from wood fibers that have been compressed together with heat and pressure.
    • It is comparable to plywood in terms of strength and stiffness, but it has a lower weight.
  • Plywood – Common wood roof sheathing that protects against fire, insects and rots as long as not exposed to standing water for too long.
    • The best plywood should be moisture-resistant and provides the same level of protection as OSB.
  • Asphalt roof shingles – Standard roof sheathing for many homes, asphalt shingles can last 20 years depending on the quality of the product and how well it is maintained.
    • They protect against fire as long as they are not exposed to open flames or extreme temperatures.
  • Fiberglass – Although less common than other types of roof sheathing, fiberglass provides an effective barrier against water and insects.
    • Fiberglass roof sheathing is thin, lightweight and non-combustible making it a good option for patios, porches and other exterior structures where fire protection is not as much of an issue.

Best Method For Replacement Of Roof Sheathing

If you have a flat roof, the best method for replacement of roof sheathing is to remove the entire compromised section of wood and re-shingle.

Since most roofs have a slant, however, depending on how bad your damage is you may only be able to replace part of your roof sheathing.

You can cut out those parts that are considered non-functional and the sheet will still provide protection.

How To Know If You Need New Roof Sheathing

If your roof sheathing is severely damaged or has been compromised by structural damage to the house, then you will need new roofing material.

This can be inspected visually during a walk-around of your exterior walls and roofs, but it may also require an inspection with specialized equipment.


The best time to replace roof sheathing is after it has become infested with mold, has medium to high amounts of moisture content, or any other sign that the wood is rotting.

If your roof can still be salvaged by replacing the siding and re-shingling the roof before it gets too bad, you should try doing so.

If your roof is already showing signs of leaks or other problems, you should replace the sheathing immediately.

When To Replace Roof Sheathing And What Does It Do