As a civil engineer, understanding the right plywood thickness is essential for a successful roofing project. In this blog, we’ll break down the importance of plywood thickness, provide practical guidance, and help you make informed decisions.


Plywood serves as the roof decking or sheathing, creating a sturdy base for your roofing materials, including shingles. The thickness of this plywood layer plays a crucial role in ensuring your roof can withstand the elements and provide reliable protection for your home.

Choosing the Right Plywood Thickness

The most common plywood thicknesses used for roof sheathing are 3/8-inch, 7/16-inch, 1/2-inch, and 5/8-inch. The choice of thickness depends on various factors, including local building codes, climate, and the type of roofing material you plan to use.

Here’s a simple guide to help you choose the appropriate plywood thickness for your roofing project:

1. Local Building Codes

Check with your local building department to determine if there are specific requirements for plywood thickness. Building codes can vary from one region to another, and compliance is essential to ensure your roof meets safety standards.

2. Roofing Material

Different roofing materials have different weight requirements. Heavier materials like slate or clay tiles may require thicker plywood to support the load. Asphalt shingles are lighter and can typically be installed on thinner plywood.

3. Roof Pitch

The pitch or slope of your roof also influences plywood thickness. Steeper roofs may require thicker plywood to provide adequate support and prevent sagging.

4. Climate Considerations

In areas with heavy snow loads or high winds, thicker plywood can offer better structural integrity and resistance to weather-related stresses.

5. Joist Spacing

The spacing between your roof’s joists can impact the choice of plywood thickness. Wider joist spacing may necessitate thicker plywood for added support.


In conclusion, the question of how thick the plywood should be under roof shingles doesn’t have a one-size-fits-all answer. It depends on a combination of factors unique to your location and roofing project. Consulting local building codes and considering your roofing material, roof pitch, climate, and joist spacing will guide you in making the right choice.

Remember, the goal is to ensure your roof provides long-lasting protection for your home. Investing in the appropriate plywood thickness is a fundamental step in achieving this goal, and it’s an area where attention to detail truly matters in the world of roofing.


As a civil engineer and roofer, I love to share the experience that I have gained through the last couple of years. In the roofing industry, practical experience is a very crucial fact that can help you a lot. Hence, I want to help you with my blog.

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