What is Sheathing on a Roof?

What is Sheathing on a Roof?

There is much more to a roof than the part that you can see. While the outermost layer of shingles or panels is the star of the show, the sublayers are essential for protection. Roof sheathing is an important component of your roof. Understanding where it is and how it works can help you resolve roof issues and maximize the life of your roof.

What is Roof Sheathing?

If you have ever seen a house under construction, you have likely seen the sheathing of the roof. Roof sheathing, also known as roof decking, is the layer of boards that lies over the joists and trusses and beneath the external surface.

The sheathing is strong enough to support the weight of the shingles or exterior panels. It’s also durable enough to withstand foot traffic from roofers, inspectors and other contractors. Without sheathing, your shingles would have nothing to hold onto. They would also sag between the joists. You wouldn’t be able to walk on your roof without falling through it.

Most roof sheathing is made of oriented strand board, or OSB. This is an engineered wood that comes in large panels. Most OSB is 7/16-inch thick and has been treated to resist moisture.

Some roofers use plywood, but this material is heavier and more costly. However, some roofing materials, such as slate, require a heftier underlayment. In these cases, plywood is preferable.

Plank sheathing is made of long, narrow planks with small gaps between them. This type of sheathing was used before plywood and OSB became popular and is not used often for modern houses.

No matter what type of sheathing you use, it should be at least ½-inch thick. Heavier roofing materials require thicker sheathing. Your roofer should check the manufacturer’s installation instructions, which will identify the required type of sheathing.

What Does Roof Sheathing Do?

Sheathing creates the roof’s foundation and offers the following benefits:

Leak Prevention

The outermost layer of roofing material, such as asphalt shingles, offers plenty of protection from the elements. But if your shingles or shakes become compromised, the decking safeguards the structure from extreme water damage.

The sheathing doesn’t protect the home from water forever, though. It’s meant to work as a unit with the other layers of roofing materials. If the sheathing develops moisture damage, it will need to be replaced.

Even Weight Distribution

The sheathing is supported by some of the strongest beams in your home, the joints and trusses. The decking distributes the weight evenly across the surface of the roof. This prevents you from puncturing the structure when you’re walking on it. It also maintains the integrity of the roof when it’s exposed to heavy precipitation loads, such as snow accumulation.

Fire Resistance

Roofing materials are rated for their fire resistance. Class A offers better protection than class B and C. In some areas that are prone to fires, builders are prohibited from using class B and C materials on the roof.

Fire-rated sheathing is engineered with fire-resistant properties and offers the following benefits:

  • Prevents flame spread
  • Combusts slowly
  • Slows the fire
  • Gives emergency responders more time
  • Reduces damage

How to Identify Roof Sheathing Problems

If your roof sheathing is compromised, the shingles or panels above it probably have problems too. An experienced roofer can identify the source of the problem and offer solutions for repairs. Your roofer should also inspect the decking when replacing a roof.

It’s not uncommon to uncover signs of sheathing problems after removing the shingles. However, you don’t always need to replace all of the sheathing. You might be able to swap out single boards in the affected areas.

Some specific signs that you need new roof sheathing are as follows:

  • You can see broken decking – Damage, such as a fallen tree limb, can crack the sheathing. You might notice that your roof is sagging. You may also spot sawdust or broken decking in the attic.
  • Water damage – Water stains on your ceilings, walls or floors indicate that there is a leak. While it could be a plumbing problem, it might be a sign that you need to replace your sheathing. Dark spots and rot that are visible from the attic are clear indicators of water damage from the roof.
  • Rot – You can often spot rot in the sheathing by shining a flashlight on it from the attic. Areas with rot will look dark or stained. If you can reach the underside of the sheathing, you can also feel for soft spots in the surface, which would indicate that you have a leak in your roof.
  • You can see light – Do you see pinpoints of light in the attic ceiling? If light is getting through, water is also penetrating the material.
  • Sagging – If your ceiling is sagging or your shingles appear to be losing their form, the roof’s underlayment is often to blame.

How to Maintain Your Roof Sheathing

You can prevent most roof sheathing problems by following these steps:

  • Insulate your roof properly – Adequate insulation prohibits condensation buildup and ice dams.
  • Ensure adequate ventilation – Without adequate ventilation, moisture collects on the roof sheathing like dew. This can weaken the underlayment and compromise the durability of the roof.
  • Repair problems promptly – Small leaks can become major concerns in a small amount of time. Moreover, sheathing damage can create issues in other parts of the home, such as wet drywall and mold growth.
  • Clean your roof regularly – Remove debris and organic growth from your roof regularly. Keep the gutters clear to promote water flow. Moss and algae buildup can damage the materials that they grow on. Clean your roof according to the manufacturer’s instructions to keep this growth at bay.
  • Install your roof correctly – Don’t install a new roof directly over the old one. Remove the shingles or exterior covering completely. This provides access to the underlayment and reveals whether the sheathing needs to be replaced.

Presidio Roofing can inspect your sheathing and recommend the proper decking for your roofing project. Contact us for a free quote today.

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