What is Roof Sheathing? (Types of Roof Sheathing and How it Works)

Have you ever wondered what roof sheathing is?

You know, the boards that cover your roof and help it to stay dry?

So, let’s take a look at the different types of roof sheathing, how they work, and why they’re so important in our homes!

Table of contents

What is roof sheathing?

Roof sheathing, also known as roof decking, is a layer of material that is installed over the roof framing of a building before the final roofing material (such as shingles or metal panels) is applied.

It serves as the structural base for the roof, providing support for the roofing materials and helping to distribute the weight of the roof evenly across the framing members.

Roof sheathing typically comes in large sheets and is usually made from wood-based materials such as plywood or oriented strand board (OSB), although other materials like metal or composite panels may also be used.

It is typically installed perpendicular to the roof framing, and the sheets are secured to the framing members using nails or screws.

Roof sheathing plays several important roles in a roof system. It provides stability and rigidity to the roof, helping to prevent sagging or warping of the framing members.

It also acts as a substrate for the attachment of the roofing materials, providing a smooth surface for installation and helping to protect the roof from moisture intrusion.

Roof sheathing can also provide some insulation and can serve as a barrier against wind-driven rain or snow, helping to protect the underlying structure from water damage.

What are the purpose and benefits of roof sheathing?

Structural support: Roof sheathing provides additional structural support to the roof framing, helping to distribute loads from the roof to the underlying framing and improving the overall stability and strength of the roof.
Base for roofing materials: Roof sheathing serves as a solid substrate for the installation of various roofing materials, such as shingles, tiles, or metal panels, ensuring proper alignment and installation of the roof covering.

Moisture resistance: Many types of roof sheathing, such as plywood and OSB, are designed to be resistant to moisture, helping to prevent water intrusion and protect the underlying roof structure from damage caused by moisture-related issues, such as rot and decay.
Insulation properties: Some types of roof sheathing, particularly those made of wood-based materials, can provide insulation properties, helping to regulate heat transfer and improve energy efficiency in the building, potentially reducing heating and cooling costs.
Ventilation benefits: Certain types of roof sheathing, such as skip sheathing, can provide ventilation benefits by allowing air to circulate between the sheathing and the roofing materials, helping to prevent moisture buildup and improve overall roof performance.

Ease of installation: Roof sheathing is typically available in large panel sizes, making it relatively easy and efficient to install, especially when compared to individual boards or other types of roofing substrates.
Fire resistance: Some types of roof sheathing, such as concrete sheathing, can offer increased fire resistance, helping to protect the roof and the underlying structure from fire damage.

Types of roof sheathing

Oriented strand board (OSB) roof sheathing

OSB is a type of wood-based panel that is commonly used as roof sheathing. It is made by compressing strands of wood with adhesive and then forming them into panels.

OSB has become popular in modern construction due to its cost-effectiveness and structural properties.

OSB roof sheathing typically comes in 4×8-foot sheets and is available in various thicknesses.

Plywood roof sheathing

Plywood is another common type of wood-based roof sheathing. It is made by layering thin sheets of wood veneer with adhesive and then pressing them together.

Plywood is known for its strength, durability, and dimensional stability. It is available in various grades and thicknesses, with the most common thicknesses for roof sheathing being 3/8″, 1/2″, 5/8″, and 3/4″.

Plywood is often used in regions with high wind or seismic activity due to its superior performance under these conditions.

Concrete roof sheathing

Concrete roof sheathing, also known as cementitious board or cement board, is a type of non-wood-based sheathing material.

It is made from a combination of cement, fibers (such as cellulose or fiberglass), and other materials due to its fire-resistant properties. It is typically heavier than wood-based sheathing and may require additional structural support.

Skip roof sheathing

Skip sheathing, also known as spaced sheathing, is a type of roof sheathing where the panels are installed with gaps or spaces between them.

It was a common method of roof sheathing in older construction practices and is still used in some regions or for certain roofing materials, such as wood shakes or wood shingles.

Skip sheathing provides ventilation and allows for air circulation beneath the roof, which can help reduce moisture buildup and extend the lifespan of the roofing materials.

Wooden board sheathing

Wooden board sheathing, also known as plank sheathing, is a traditional type of roof sheathing that uses solid wood planks as the roof decking.

It was commonly used in older construction practices but is less common in modern construction due to the availability of other more cost-effective and efficient sheathing materials like plywood or OSB.

Wooden board sheathing requires careful installation to ensure proper spacing and fastening of the planks to provide structural stability and support for the roofing materials.

Table: Pros and cons of different roof sheathings

Type of Roof Sheathing	Pros	Cons
Plywood Sheathing	High strength and durability, resistant to moisture and insects, provides good insulation	Can be more expensive, requires proper sealing of seams, limited availability of large panel sizes
Oriented Strand Board (OSB) Sheathing	Cost-effective, resistant to moisture, available in large panel sizes	Lower overall strength compared to plywood, susceptible to swelling and delamination in extreme moisture conditions
Concrete Sheathing	Fire-resistant, durable and long-lasting, provides high strength and stability	Heavy and requires additional structural support, more expensive compared to wood-based sheathing, requires skilled installation
Skip Sheathing	Ventilation benefits, can be cost-effective, can be used with certain roofing materials	Reduced structural support, reduced insulation, requires more frequent maintenance
Wooden Board Sheathing	Aesthetically pleasing, natural material, can be custom-sized	Limited availability, requires regular maintenance, susceptible to pests, labor-intensive installation

The table provides a concise overview of different types of roof sheathing, including their pros and cons

Pros and cons of different types of roof sheathing explained

1. Oriented strand board (OSB) roof sheathing

Pros:

Cost-effective: OSB is generally less expensive than plywood, making it a budget-friendly option for roof sheathing.

Structural strength: OSB has good structural properties and can provide adequate support for roofing materials.
Availability: OSB is widely available and can be found at most lumberyards and building supply stores.
Consistent thickness: OSB panels are manufactured to precise thicknesses, which can make for more consistent installation and fewer irregularities.

Cons:

Moisture susceptibility: OSB can be more susceptible to moisture absorption than plywood, which may require additional precautions to prevent water damage.
Edge swelling: OSB can swell along the edges when exposed to moisture, which can affect its performance and appearance.

Limited exposure rating: OSB may have limited exposure ratings, which means it may not be suitable for prolonged exposure to the elements during construction or if the roof is left uncovered for an extended period.

2. Plywood roof sheathing

Pros:

Strength and durability: Plywood is known for its strength and dimensional stability, making it a reliable choice for roof sheathing.

Moisture resistance: Plywood has good resistance to moisture and can withstand exposure to the elements during construction.
Wide range of thicknesses: Plywood is available in various thicknesses, allowing for flexibility in meeting structural and performance requirements.
Long-term performance: Plywood has a proven track record of long-term performance in roof sheathing applications.

Cons:

Cost: Plywood tends to be more expensive than OSB, which can impact the overall cost of the roof system.
Slightly heavier: Plywood is slightly heavier than OSB, which may add some weight to the overall roof system.

Limited availability of larger panels: Plywood panels may be limited in size compared to OSB, which can affect installation efficiency and material waste.

3. Concrete roof sheathing

Pros:

Fire resistance: Concrete roof sheathing is highly fire-resistant, which can provide added protection in regions with high fire risk.

Moisture resistance: Concrete roof sheathing is resistant to moisture, which can help prevent rot and decay.
Durable: Concrete roof sheathing is durable and can withstand harsh weather conditions, making it suitable for long-term use.
Termite resistance: Concrete is not susceptible to termite damage, providing an advantage in termite-prone areas.

Cons:

Weight: Concrete roof sheathing is considerably heavier than wood-based sheathing, which may require additional structural support.
Limited insulation: Concrete has low insulation properties compared to other materials, which may require additional insulation layers to achieve desired thermal performance.

Cost: Concrete roof sheathing tends to be more expensive than wood-based sheathing materials, which can impact the overall cost of the roof system.
Installation complexity: Installation of concrete roof sheathing may require special equipment, expertise, and additional time compared to wood-based sheathing.

4. Skip roof sheathing

Pros:

Ventilation: Skip roof sheathing provides ventilation and allows for air circulation beneath the roof, which can help to reduce moisture buildup and prolong the lifespan of the roofing materials.
Traditional aesthetics: Skip roof sheathing is commonly used with wood shakes or shingles and can provide a traditional or rustic appearance to the roof.
Cost-effective: Skip roof sheathing may require less material compared to full coverage sheathing, which can result in cost savings.

Cons:

Reduced structural support: Skip roof sheathing may provide less structural support compared to full coverage sheathing, as there are gaps or spaces between the panels.
May require additional layers: Skip roof sheathing may need additional layers, such as a secondary layer of sheathing or an underlayment, to provide adequate support and protection for the roofing materials.

Reduced insulation: Skip roof sheathing may not provide as much insulation compared to full coverage sheathing, as there are gaps or spaces between the panels, which can affect energy efficiency.
Maintenance: Skip roof sheathing may require more frequent maintenance to ensure that debris, leaves, or pests do not accumulate in the gaps or spaces between the panels.

5. Wooden Board Sheathing

Pros:

Aesthetics: Wooden board sheathing can provide a traditional and rustic appearance to the roof, which may be desirable for certain architectural styles.
Natural material: Wooden board sheathing is made from natural wood, which is a renewable and sustainable resource.
Can be used with various roofing materials: Wooden board sheathing can be used with a variety of roofing materials, such as wood shingles, shakes, or metal roofing.

Can be custom-sized: Wooden board sheathing can be custom-sized to fit specific roof designs and shapes.

Cons:

Limited availability: Wooden board sheathing may be less commonly available compared to other types of sheathing materials, which may impact accessibility and cost.

Maintenance: Wooden board sheathing requires regular maintenance, including staining or painting, to protect against moisture, rot, and decay.
Susceptibility to pests: Wooden board sheathing may be susceptible to pests such as termites or wood-boring insects, which can affect its performance and durability.
Labor-intensive installation: Installation of wooden board sheathing may require additional labor compared to other types of sheathing materials, as it may need to be custom-cut and installed individually.

How roof sheathing works

Roof sheathing works by providing structural support, creating a base for roofing materials, and helping to distribute loads from the roof to the underlying framing, while also offering insulation, moisture resistance, and ventilation benefits depending on the type of sheathing used.

The sheathing is attached securely to the rafters or trusses, creating a solid substrate that supports the weight of the roof and any applied loads, such as snow, wind, or foot traffic.

Roof sheathing also serves as a base for the installation of roofing materials, such as shingles, tiles, or metal panels, providing a smooth surface and helping to ensure proper alignment and installation of the roof covering.

Also, roof sheathing can provide insulation properties, helping to regulate heat transfer and improve energy efficiency in the building.

What is the best type of roof sheathing for residential homes?

Both plywood and OSB have their advantages and disadvantages, and the best choice for residential homes can depend on factors such as local building codes, climate, budget, and personal preferences.

Plywood is generally considered to have better moisture resistance and dimensional stability, which may make it more suitable for areas with high moisture or extreme weather conditions. OSB, on the other hand, is typically more affordable and widely available, making it a popular choice for many residential projects.

Plywood is made from layers of wood veneers that are bonded together with adhesive. It is known for its strength, durability, and resistance to moisture when properly sealed or treated.

Plywood roof sheathing typically comes in standard thicknesses of 1/2 inch, 5/8 inch, and 3/4 inch, and is available in various grades and types, such as CDX (common grade), ACX (premium grade), and pressure-treated plywood (for added moisture resistance).

How do I know if I need to replace my roof sheathing?

Broken or damaged boards: If you notice any broken, cracked, or splintered roof sheathing boards, it may be a sign of structural damage that requires replacement. Damaged boards can compromise the integrity of the roof system and may not provide adequate support for the roofing materials.

Water damage or roof leaking: Water damage on the roof sheathing, such as dark stains, discoloration, or mold growth, can indicate water intrusion and potential rotting of the sheathing material. Roof leaks can also cause damage to the roof sheathing, and if left unaddressed, may require replacement to prevent further structural damage.
Wood rotting: Wood rot is a common issue with roof sheathing, especially in areas with high moisture or prolonged exposure to water. If you notice signs of wood rot, such as soft spots, decayed areas, or a musty odor, it may be an indication that the sheathing needs replacement to maintain structural integrity.
Holes in the roof (sunlight shining through): Holes or gaps in the roof sheathing can allow sunlight to shine through into the attic, indicating a breach in the roof’s integrity. This can lead to water infiltration, pest infestation, and other issues, and may require replacement of the damaged sheathing.

Ceiling sagging or depressed roof line: If you notice any signs of a sagging ceiling or a depressed roof line, it may indicate a problem with the roof sheathing. This could be due to moisture damage, rotting, or structural issues, and may require immediate attention and potential replacement of the affected sheathing.

How much does roof sheathing cost?

Plywood Thickness (in.)	Price
5/32	$18.51
1/5	$25.98
11/32	$22.03
15/32	$23.95
1/2	$35.58

This table shows the thickness of plywood and the cost of each.

What materials do I need for roof sheathing installation?

Roof sheathing panels (e.g., plywood, OSB, or other material based on your chosen type of roof sheathing)
Nails, screws, or other fasteners suitable for attaching the sheathing to the roof framing

Roofing underlayment (e.g., felt paper or synthetic underlayment) to provide an additional layer of protection against moisture
Roofing nails or staples to secure the underlayment to the sheathing
Flashing materials (e.g., metal or rubber flashing) to provide waterproofing at roof penetrations such as vents, chimneys, and valleys

Ridge vents or other ventilation materials, if needed for proper attic ventilation
Safety equipment such as gloves, eye protection, and fall protection gear, as appropriate for the installation process
Tools such as a circular saw, hammer, screwdriver, nail gun, and measuring tape for cutting and installing the sheathing panels and fasteners.

How many new sheathing boards will my roof need?

A common method to estimate the number of plywood sheathing panels needed for a roof is to divide the total roof area in square feet by 32, which is the area of a standard plywood panel measuring 4 feet by 8 feet.

This method provides a rough estimate and can be helpful for quickly determining the approximate number of panels needed for a given roof area.

However, it’s important to note that this method assumes standard panel sizes and does not account for waste or cutting allowances, which may vary depending on the specific installation requirements.

Let’s assume you have a roof with a total area of 2,000 square feet that you want to sheath with plywood. Using the common method of dividing the total roof area by 32 (the area of a standard plywood panel), the calculation would be as follows:

Total roof area: 2,000 square feet Plywood panel size: 4 feet by 8 feet

Number of plywood panels needed = Total roof area / Area of one plywood panel

Number of plywood panels needed = 2,000 square feet / (4 feet x 8 feet)

Number of plywood panels needed = 2,000 square feet / 32 square feet

Number of plywood panels needed = 62.5 panels (rounded up to the nearest whole number)

So, according to this method, you would need approximately 63 plywood panels (rounded up from 62.5) to sheath the entire roof, which has a total area of 2,000 square feet.

It’s always a good idea to purchase a few extra panels to account for waste, cutting allowances, and unexpected needs during the installation process.

How thick should the roof sheathing be?

The thickness of roof sheathing depends on various factors, such as the type of roofing material, local building codes, and structural requirements. In general, the most common thicknesses for roof sheathing are 3/8 inch (9.5 mm), 1/2 inch (12.7 mm), 5/8 inch (15.9 mm), and 3/4 inch (19.1 mm). Thicker sheathing is generally used for heavier roofing materials or in areas with higher wind or snow loads.

Here are some general guidelines for the recommended thickness of roof sheathing based on the roofing material:

Asphalt shingles: 3/8 inch (9.5 mm) or 1/2 inch (12.7 mm) plywood or OSB sheathing is commonly used.
Wood shingles or shakes: 1/2 inch (12.7 mm) plywood or OSB sheathing is typically recommended.

Metal roofing: 1/2 inch (12.7 mm) plywood or OSB sheathing is commonly used, but thicker sheathing may be required for longer spans or heavy loads.
Tile or slate roofing: 5/8 inch (15.9 mm) or 3/4 inch (19.1 mm) plywood or OSB sheathing is usually recommended due to the weight of these roofing materials.
Concrete or clay tile roofing: 3/4 inch (19.1 mm) or thicker plywood or OSB sheathing is typically required due to the heavy weight of these roofing materials.

How long does roof sheathing last?

Plywood: Plywood roof sheathing, when properly installed and maintained, can last for 20 to 40 years or even longer, depending on factors such as exposure to moisture, sun, and other environmental conditions.
Oriented strand board (OSB): OSB roof sheathing typically has a similar lifespan to plywood, with an average lifespan of 20 to 40 years or more, depending on various factors.
Structural insulated panels (SIPs): SIPs are a type of roof sheathing that consists of a layer of foam insulation sandwiched between two layers of oriented strand board (OSB) or other materials. SIPs are known for their energy efficiency and durability, and can last for 50 years or more with proper maintenance.

Particleboard: Particleboard is a less common type of roof sheathing material that is generally less durable compared to plywood or OSB. Particleboard roof sheathing typically has a shorter lifespan of 10 to 20 years, depending on the quality of the material and the installation.

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Author: Logan

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