Table of Contents
Introduction
This tool helps you estimate the number of roof sheathing panels required for a project. Roof sheathing panels are typically plywood or OSB, with each whole panel measuring 4 feet x 8 feet (1220 mm x 1440 mm). Those are the panel dimensions that this calculator uses.
Input the roof’s width, length, slope, and an appropriate waste factor and the calculator determines the total roof surface area and the number of sheathing panels needed. The calculator supports both U.S. and metric measurements. It automatically generates and uses the correct roof slope multiplier when determining roof area.
The calculator works for gable roofs, hip roofs, shed roofs…basically any roof with a uniform pitch. Roof sections with different pitches should be calculated separately using the “Add another roof section” button and then added together.
Roof Sheathing Calculator
Wood Panel Roof Sheathing Fact Sheet
1. Purpose and Function
Wood panel sheathing serves as the structural substrate for roofing systems. It transfers loads from the roofing materials to the roof framing, provides a nailable surface for shingles or underlayment, and contributes to the diaphragm action of the building for lateral stability.
2. Standard Materials
- Plywood: Manufactured with wood veneers bonded with exterior-grade adhesives.
- Oriented Strand Board (OSB): Composed of wood strands compressed with waterproof adhesives. It is widely used due to cost-effectiveness and dimensional uniformity.
Both materials must meet the performance standards specified by organizations such as the APA – The Engineered Wood Association.
3. Panel Thickness and Span Ratings
- Standard Panel Thicknesses:
- 3/8 in. normally allowed for framing spaced 16 in. o.c.
- 7/16 in. to 15/32 in. for 24 in. o.c. spacing (common for OSB)
- 5/8 in. or thicker may be used where enhanced rigidity is required.
- Span Ratings: Indicated on each panel, such as “24/16,” meaning suitable for 24 in. o.c. roof framing or 16 in. o.c. subfloor framing.
Thicker panels are required for heavier roofing materials and wider rafter spacing.
4. Panel Installation
- Orientation: Panels should be installed with the long dimension perpendicular to the framing members to maximize load-carrying capacity.
- Staggered Joints: Panels must be staggered so that end joints do not align across adjacent rows.
- Panel Gaps: A minimum gap of 1/8 in. should be left at panel ends and edges to accommodate moisture-induced expansion.
- Edge Support: Panels installed over framing spaced 24 in. o.c. may require H-clips or tongue-and-groove edges for added support.
5. Fastening Requirements
- Nailing: Panels must be nailed to each rafter or truss using corrosion-resistant nails.
- Typical Nail Schedule:
- Panel Ends (fully-supported edges): nails spaced 6 inches on center
- Field (intermediate framing members): nails spaced 12 in. o.c.
- Nail size: 8d common nails (or equivalent), unless otherwise specified.
Avoid overdriving nails or driving them at an angle, as this can compromise the panel’s holding strength.
6. Wood Panels as Roof Deck
- Suitable for use under most types of roofing, including asphalt shingles, tile, and metal panels, as long as loading, ventilation, and moisture protection requirements are met.
- When used in low-slope assemblies, special considerations may be required to ensure adequate slope and waterproofing.
7. Ventilation and Moisture Considerations
- Roofs must be adequately ventilated beneath the sheathing to reduce condensation risk.
- Panels exposed to high humidity or potential water intrusion should be rated for exterior exposure.
About the Author
Jack Gray spent 20 years as a principal roof consultant with the Moriarty Corporation, an award-winning building enclosure consultant firm founded in 1967. Mr. Gray has worked in the roofing industry for over 25 years, with training and practical experience in roof installation, roof inspection, roof safety, roof condition assessment, construction estimating, roof design & specification, quality assurance, roof maintenance & repair, and roof asset management. He was awarded the Registered Roof Observer (RRO) professional credential in 2009. He also served as an infantry paratrooper in the 82nd Airborne Division and has a B.A. from Cornell University.