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What is Under My Siding? Understanding Sheathing Types and Their Condition

Celotex Wall Sheathing Material

While it is an often overlooked aspect of a new siding installation, many of our customers often ask us about what will be used under their siding for extra protection of their home. In this post, we’ll explore the types of exterior sheathing commonly found in homes and how they’ve evolved over time. From the plank sheathing used in older homes to modern materials like OSB and foam board, this will provide a deeper understanding of how different sheathing options contribute to the structure and efficiency of a home.

When constructing or renovating a home, exterior sheathing is an essential component that provides structural support and insulation. Exterior sheathing is a board or panel made from various materials, installed over the exterior walls of a building. Its primary functions include lending structural stability and insulating the home. Let’s dive into the layers that make up your home’s exterior.

Historical Sheathing in Old Houses: Plank Sheathing

In older houses, especially those built before the 1930s, plank sheathing was commonly used. This type of sheathing typically consists of 1×6 or 1×8 wooden planks nailed directly to the framing. Known for its durability and strength, plank sheathing provides a sturdy base for siding and roofing materials. However, these planks can suffer from warping, splitting, and loosening over time, particularly if exposed to moisture. Regular inspection is crucial to ensure the planks remain in good condition, as any deterioration can compromise the building’s structural integrity.

Sheathing from 1930 to 1980: The Era of Celotex

From the 1930s to the 1980s, Celotex became a popular sheathing material. Because the Celotex Corporation, which produced an insulation board made from bagasse (sugar cane waste), was founded in 1920 in Chicago, Illinois, this material is found to this day in numerous homes throughout our Chicagoland area. This fiberboard, often referred to simply by its brand name, was widely used for its insulating properties and ease of installation.

Despite its benefits, Celotex products came under scrutiny in the 1980s due to asbestos content, leading to high-profile lawsuits and ultimately Chapter 11 bankruptcy in 1990. After emerging from bankruptcy in 1996, Celotex continued to operate under new ownership and restructuring, with the brand now owned by Saint-Gobain. Celotex insulation boards and insulated plasterboards remain in use today.

Celotex Wall Sheathing Material

Modern Sheathing: Evolution and Innovation

Today, sheathing materials have evolved significantly, offering improved performance and safety. Modern sheathing options include oriented strand board (OSB), plywood, foam board, gypsum, and structural fiberboard. These materials provide better moisture resistance, structural integrity, and energy efficiency compared to older options like plank and Celotex sheathing.

Types of Exterior Wall Sheathing

1. Oriented Strand Board (OSB)

  • Benefits: OSB is made from wood strands bonded with resin and wax, providing strength and durability.
  • Installation: Installed vertically with slight gaps to allow for expansion, it forms a solid nailing base for siding.
  • Drawbacks: OSB can swell if exposed to moisture, requiring prompt siding installation.

2. Structural Fiberboard

  • Benefits: Made from plant cellulose fibers, it offers some insulating and sound-reducing properties.
  • Installation: Heavy and requires at least two people for installation, it is installed vertically without spacing between sheets.
  • Drawbacks: Requires careful handling to avoid stripping out screw holes.

3. Plywood

  • Benefits: Plywood is dimensionally stable and provides excellent structural support.
  • Installation: Easy to install vertically, with nails placed every 6 inches on edges and every 12 inches in the center.
  • Drawbacks: Requires house wrap for additional moisture protection.

4. Foam Board

  • Benefits: Provides significant insulation, creating a tight building envelope.
  • Installation: Installed over structural sheathing or directly to studs with foil facing determined by siding type.
  • Drawbacks: Requires specific installation techniques to prevent moisture infiltration.

5. Gypsum Sheathing

  • Benefits: Offers fire resistance and additional stability.
  • Installation: Can be installed vertically or horizontally with minimal joints, using screws.
  • Drawbacks: Requires careful cutting and handling due to its brittle nature.

6. Diagonal Tongue and Groove

  • Benefits: Provides historical authenticity and strong interlocking support.
  • Installation: Labor-intensive, with each board fitted and nailed into place individually.
  • Drawbacks: Higher installation time and cost compared to modern materials.

Making Sense of Your Options

Choosing the right type of sheathing depends on the specific needs of your project, including structural support, insulation, and historical accuracy. Each material has its own advantages and installation requirements, so understanding these can help you make an informed decision.
Exterior sheathing plays a vital role in every home exterior, contributing to the structural stability, energy efficiency, and overall durability of the building. Whether you’re working on a new construction or renovating an older home, selecting the appropriate sheathing material is essential for ensuring long-term performance and comfort.
In conclusion, the choice and condition of exterior sheathing are critical components in the construction and maintenance of any home. From the durable plank sheathing of older houses to the versatile and insulating options available today, each material offers unique benefits and challenges. Understanding the history, characteristics, and installation requirements of different sheathing types can help homeowners and builders make informed decisions that enhance the structural integrity, energy efficiency, and longevity of a building. By regularly inspecting and maintaining sheathing, you ensure that your home remains a safe, comfortable, and resilient space for years to come.

Have additional questions? We’re always happy to help! Feel free to contact us at 847.847.2883 or contact us online. Looking forward to speaking with you soon!

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