Roof Decking & Sheathing: Useful Information Guide
By Jack Gray, Roof Online Editor • Last updated May 15, 2023
Overview of Roof Deck & Sheathing
The deck is the foundation of all standard roofing systems. The roof’s performance is largely dependent on the foundation’s integrity, just like the performance of a building itself.
The type of roof decking used is usually determined by the materials used in the building, the design of the building, and the purpose of the building.
Choosing a deck type is not based solely on its physical properties, appearance, or price. Its effect on the installation and performance of the roof system should be considered as well.
Roof decking is considered to be the bottom (and foundational) layer of a roof assembly. It is not considered to be a part of a roof system, and that’s the main difference between a roof assembly and a roof system.
The roof deck is installed on top of the roof framing or roof support system (the rafters, trusses, or joists). Roof decks are typically made of steel, concrete, or wood.
The roof deck is usually the only part of a roof that is considered to have a structural function. The roof system itself has an extremely important function, but it isn’t structural.
The structural roof support system is not normally considered a part of the roof. On a house, for instance, the rafters or trusses are classified as a part of the framing.
The roof deck provides a stable and durable platform that forms the substrate for the attachment of the roof system. It serves as a structural base that supports the weight of the roof covering and any live loads, such as accumulated snow or materials loaded onto the roof during a roof installation.
The roof decking helps to tie the entire building structure together by connecting the roof support system components to each other and to the walls of the building. This helps the building resist lateral forces, such as those caused by wind or earthquakes. It distributes those forces to the roof framing system, mitigating stress or strain that could otherwise cause structural damage or failure.
An appropriately-designed roof deck can also help to improve the energy efficiency and performance of the building as a whole. It can act as a reflective barrier, reducing the amount of heat that is absorbed through the roof, and can serve as an air or vapor barrier, creating a more airtight seal that improves the insulation and ventilation performance of the building.
To summarize: the function of roof decking in a roofing system is to provide a sturdy and stable substrate for the roof covering, to support live loads and resist lateral forces, and to contribute to the energy efficiency and performance of the building.
Related Pages
External Sources & References for Roof Deck & Sheathing
Note (5/15/2023): A couple of the links to IIBEC Interface articles are not currently working, as IIBEC has recently changed their website structure. We’ve removed those active links for now, but we’re leaving the references in place in case we can link to them again in the future.
1. Book Recommendation: Manual of Low-Slope Roof Systems: Fourth Edition by C.W. Griffin & Richard Fricklas
2. General: For a good overview article describing various types of roof deck, see “Roof Decks: Don’t Underestimate the Backbone of the Roof System” by Thomas W. Hutchinson. The article is from 2014 and is archived on the Roofing Magazine website.
3. General: The National Roof Deck Contractors Association website has some useful information about various roof deck types.
4. Building Codes: Commercial: Lumber sheathing: see 2304.8.2 Structural Roof Sheathing in the 2018 International Building Code.
5. Building Codes: Commercial: Steel roof deck: see 2210.1.1.2 Steel Roof Deck in the 2018 International Building Code.
6. Building Codes: Residential: Wood sheathing (wood plank, plywood and OSB): see Section R803 Roof Sheathing in the 2018 International Residential Code.
7. Clay Tile (Structural): See “Roof Decks: A to Z – Part 3: Structural Clay Tile and Plywood” by Lyle D. Hogan, Donald Kilpatrick, and Richard Koziol in the November 2011 issue of IIBEC Interface, the technical journal of IIBEC (formerly RCI, Inc.).
8. Concrete: Cast-in-Place Concrete: See “Roof Decks: A to Z – Part VII: Cast-in-Place Structural Concrete” by L. D. Hogan and Rob Kennerly in the April/May 2015 issue of IIBEC Interface.
9. Concrete: Post-Tensioned Concrete: See “Roof Decks: A to Z – Part XI: Post-Tensioned Concrete” by L. D. Hogan in the July 2018 issue of IIBEC Interface.
10. Concrete: Precast Concrete Planks: See “Roof Decks: A to Z – Part 2: Wood Planks and Precast Concrete Planks” by Lyle D. Hogan in the April 2011 issue of IIBEC Interface, the technical journal of IIBEC (formerly RCI, Inc.).
11. Fiberglass-Reinforced Plastic: “FRP Roof Deck: A Solution for Challenging Conditions” is a decent starting point for information about this type of roof deck. From the November 2011 issue of IIBEC Interface and available on the IIBEC website. (Note that the author was employed by an FRP manufacturer at the time the article was published.)
12. Gypsum: Poured Gypsum: See “Roof Decks: A to Z – Part 4: Poured Gypsum” by Lyle D. Hogan in the October 2012 issue of IIBEC Interface.
13. Lightweight Insulating Concrete: See “Roof Decks: A to Z – Part 1: LWIC and AWC” by Lyle D. Hogan in the September 2010 issue of IIBEC Interface.
14. Lightweight Insulating Concrete: “Lightweight Insulating Cellular Concrete: A Seamless Roof Deck Installation” by Leo A. Legatski is a good basic introduction to this material. Available on the IIBEC website in the May 2000 issue of IIBEC Interface.
15. OSB/Plywood: Great article for history and comparison: “Choosing Between Oriented Strandboard and Plywood” by Paul Fisette is available on the website of the Building and Construction Technology Program at UMASS Amherst.
16. Plywood: See “Roof Decks: A to Z – Part 3: Structural Clay Tile and Plywood” by Lyle D. Hogan, Donald Kilpatrick, and Richard Koziol in the November 2011 issue of IIBEC Interface.
17. Steel: “Fastening Steel Deck” is a decent short article from 2015 available on the Structure Magazine website.
18. Steel: “Fundamentals of Steel Construction” by Lyle D. Hogan is a must-read article for anyone involved in penetrating or replacing the roof where there’s a steel roof deck. From the May 2001 issue of IIBEC Interface.
19. Steel: The SDI Manual of Construction with Steel Deck is an excellent, easy-to-follow source of technical information about steel roof decks. It was produced by the Steel Deck Institute.
20. Steel: Standards: American National Standards Institute/Steel Deck Institute – RD – 2017 Standard for Steel Roof Deck.
21. Wood Planks: See “Roof Decks: A to Z – Part 2: Wood Planks and Precast Concrete Planks” by Lyle D. Hogan in the April 2011 issue of IIBEC Interface.
22. Wood Planks: “Tongue and Groove Roof Decking” by the American Forest & Paper Association is 12 pages of good technical info on the website of the American Wood Council.