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  • Writer's pictureD&G Exteriors

Roofing Plywood: An Overview of Types and Uses

Roofing plywood is an essential material in the construction of a sturdy and long-lasting roof. Plywood is a type of engineered wood made from thin layers of wood veneer that are glued together to form a strong and durable sheet. Roofing plywood is specifically designed to withstand the harsh elements of the weather and provide a solid base for the roof covering.


Roofing plywood is used as the roof sheathing, which is the layer of material that is attached to the roof rafters and provides a flat surface for the installation of the roof covering, such as shingles. The thickness and grade of the plywood used for roofing depend on the spacing of the roof rafters, the load capacity of the roof, and the type of roof covering that will be installed.


Choosing the right type of roofing plywood is crucial to ensure the stability and durability of the roof. The most commonly used types of roofing plywood are CDX plywood and OSB (oriented strand board) plywood. CDX plywood is made from softwood and has a rough surface that provides good grip for the roof covering. OSB plywood is made from wood strands that are arranged in layers and glued together, providing a smooth and uniform surface for the roof covering.


Types and Grades of Roofing Plywood


When it comes to choosing the right roofing plywood, there are a few types and grades to consider. Each type of plywood has its own unique characteristics and is suitable for different applications. In this section, we will explore the most common types and grades of roofing plywood.


CDX Plywood


CDX plywood is the most common type of plywood used for roofing. The letters "CDX" stand for "C-D Exposure 1". This means that the plywood has a C-grade front face and a D-grade back face, and it is suitable for exposure to weather for up to 90 days. CDX plywood is made from softwood veneers and is typically available in thicknesses ranging from 1/4 inch to 1 1/4 inch.


Oriented Strand Board (OSB)


Oriented Strand Board, or OSB, is another type of plywood that is commonly used for roofing. OSB is made from small strands of wood that are glued together under high pressure to create a strong and durable panel. Unlike CDX plywood, OSB has no visible grain and is typically available in thicknesses ranging from 7/16 inch to 1 inch.


Marine Grade Plywood


Marine grade plywood is a high-quality plywood that is specifically designed for use in wet and humid environments. It is made from hardwood veneers and is bonded with waterproof glue, making it resistant to water damage and rot. Marine grade plywood is typically available in thicknesses ranging from 1/4 inch to 3/4 inch.


When it comes to choosing the right grade of roofing plywood, it is important to consider the intended use and the load requirements of the roof. Plywood grades are based on the quality of the face and back veneers, as well as the number of defects in the panel. The most common grades of plywood are A, B, C, and D. A-grade plywood is the highest quality and has no visible defects, while D-grade plywood has the most defects and is typically used for structural applications where appearance is not a concern.


Plywood Properties for Roofing


When it comes to roofing, plywood is a popular choice due to its durability, strength, and moisture resistance. Plywood is made by gluing together thin layers of wood veneer, which are stacked at right angles to each other. This construction method gives plywood its strength and durability.


Thickness and Size


Plywood thickness for roofing varies depending on the load requirements and rafter spacing. According to the International Residential Code, roofs should be covered with a minimum of 7/16" thick plywood. However, 3/8 inch is the standard size for most roofs in areas with light load requirements on rafters at 16" centers. 1/2 inch is the minimum, while 5/8 inch is the most commonly used with rafters spaced at 24" centers. For heavy load-related areas, regardless of rafter spacing, 3/4-inch plywood is recommended. The most commonly used sizes of plywood for roofing are 4×8 feet and 4×10 feet.


Moisture Resistance


Moisture-resistant plywood is recommended for roofing applications. This type of plywood is treated with chemicals that make it resistant to moisture. This is important because moisture can cause the plywood to warp, rot, or decay over time. Moisture-resistant plywood is also less likely to develop mold or mildew, which can be a health hazard.


Strength and Durability


Plywood for roofing must be durable and strong enough to withstand the elements. The quality of the plywood depends on the quality of the veneer used, the type of glue used, and the number of knots in the wood. Plywood with fewer knots is generally stronger and more durable than plywood with more knots. The glue used to bond the veneer layers together must also be strong and durable to ensure the plywood stays intact over time.


In summary, when choosing plywood for roofing, it is important to consider its thickness, size, moisture resistance, strength, and durability. Moisture-resistant plywood is recommended to prevent damage from moisture. Plywood with fewer knots and strong glue is generally stronger and more durable. By considering these factors, one can ensure that the plywood used for roofing is of good quality and will last for many years.


Installation and Maintenance


Preparing for Installation


Before installing the roofing plywood, it is important to ensure that the framing is sturdy and in good condition. Any damaged or rotten wood should be replaced before proceeding with the installation. Additionally, the roof should be water-tested to ensure that there are no leaks. Safety should also be a top priority during installation, and appropriate safety gear, such as hardhats and safety harnesses, should be worn.


Laying the Sheathing


When laying the sheathing, it is important to ensure that it is properly aligned and nailed down securely. The sheathing should be installed perpendicular to the rafters or trusses, with a 1/8-inch gap between each sheet to allow for expansion. Roofing felt should be installed over the sheathing to provide an additional layer of protection against water penetration.


Long-Term Care


Proper maintenance is essential for ensuring the longevity of the roofing plywood. Regular inspections should be conducted to check for any signs of damage or wear, and any issues should be addressed promptly. It is also important to keep the roof clean and free of debris, as this can contribute to water damage and other problems. If any repairs or replacements are needed, it is best to hire a professional to ensure that the work is done safely and correctly.


Roofing Performance Factors


When it comes to choosing the right roofing plywood, there are several factors that should be taken into consideration to ensure optimal performance. The following subsections outline some of the most important factors.


Load and Stress


Roof loads can be a significant factor in determining the appropriate thickness of roofing plywood to use. Heavy snow loads, for example, can place a significant amount of stress on the roof, and thicker plywood may be required to prevent damage. Additionally, plywood with higher shear strength may be necessary to withstand high winds and other types of stress.


Weather Impact


Weather is another important factor to consider when selecting roofing plywood. Plywood that is exposed to rain and other forms of moisture can become saturated, which can lead to warping or other types of damage. For this reason, it is important to choose plywood that is designed to withstand wet conditions. Fire-resistant and fire-retardant (FRT) plywood is also available for use in areas that are prone to wildfires.


Fire Resistance


Fire resistance is an important consideration for any roofing material. Plywood that is treated with fire-retardant chemicals can help to prevent the spread of fire and provide additional protection in the event of a fire. Some types of FRT plywood are also designed to be more resistant to charring and other types of damage from fire.


In summary, when choosing roofing plywood, it is important to consider factors such as load and stress, weather impact, and fire resistance. By selecting the right type of plywood for the job, it is possible to ensure optimal performance and long-lasting protection for your roof.



Choosing the Right Plywood for Your Roof



Choosing the right plywood for your roof is critical for ensuring the durability and longevity of your roof. The wrong choice can lead to costly repairs or even a complete replacement in the future. The following factors should be considered when selecting plywood for your roof:


Thickness


Plywood thickness is measured in inches and typically ranges from 1/8 inch to 1 inch. The most common thicknesses used for roofing are 1/2 inch and 3/4 inch. It is important to note that the thickness of the plywood should be appropriate for the rafter spacing and the load requirements of the roof. For heavy load-related areas, 3/4-inch plywood is recommended regardless of rafter spacing, while 1/2 inch is the minimum.


Grade


Plywood is graded based on its surface grade and intended use. For roofing, CDX grade plywood is the recommended size. CDX plywood is a popular type of plywood that has a C-grade surface on one side, which is acceptable for use under asphalt shingles and roofing felt.


Type


There are two types of plywood available for roofing: general plywood and structural plywood. General plywood is suitable for roofs with a low pitch and light load requirements, while structural plywood is recommended for roofs with a steeper pitch and heavy load requirements.


Size


Plywood dimensions can be confusing, as they are often not the same as the actual size. The most common sizes for roofing are 4x8 feet, 5x8 feet, and 4x10 feet. The size of the plywood should be appropriate for the size of the roof deck.


Advantages and Disadvantages


Plywood is easy to work with, lightweight, and provides stiffness to the roof. However, it can be expensive, and the quality can vary depending on the manufacturer. It is important to choose a trusted brand and to buy from a reputable website.


Cost


The cost of plywood can vary depending on the size, type, and quality. It is important to consider the cost when choosing the right plywood for your roof.


Experience


It is important to hire experienced builders or roofers who have knowledge of the appropriate plywood for your roof. They can help you choose the right plywood and ensure the structural stability of your roof.


In summary, choosing the right plywood for your roof is crucial for ensuring the durability and longevity of your roof. The thickness, grade, type, size, advantages, disadvantages, cost, and experience should be considered when selecting plywood for your roof.


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