Building Code Glossary
Positive Roof Drainage: Building Code Definition
How the IBC 2009, IRC 2009 define positive roof drainage, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Positive roof drainage is a defined term in the International Building Code (IBC) 2009, in Roof Assemblies and Rooftop Structures. The code's own words are: “The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.” The IRC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 4 chapters of this corpus, most often in Roof Assemblies and Rooftop Structures (IBC 2009), Roof Assemblies (IRC 2009), Definitions (IBC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Positive Roof Drainage — IBC 2009, Roof Assemblies and Rooftop Structures:
The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Positive Roof Drainage, in identical words.
| Code | Where it is defined | Definition |
|---|---|---|
| IBC 2009 | Roof Assemblies and Rooftop Structures | The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation. |
| IRC 2009 | Definitions | The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation. |
Where positive roof drainage is used in the code
The term appears in 4 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Roof Assemblies and Rooftop Structures | IBC 2009 | 3 |
| Roof Assemblies | IRC 2009 | 2 |
| Definitions | IBC 2009 | 1 |
| Definitions | IRC 2009 | 1 |
The terms positive roof drainage is built out of
The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what positive roof drainage covers:
- Roof Deck — IBC 2009: The flat or sloped surface not including its supporting members or vertical supports.
- Slope — IRC 2009: The fall (pitch) of a line of pipe in reference to a horizontal plane.
Positive Roof Drainage: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IBC | Roof Assemblies and Rooftop Structures | |
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Roof Assemblies and Rooftop Structures (IBC 2009) | |
| Re-check the requirement that uses it | Roof Assemblies (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IBC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Roof Deck | |
| Confirm the dependent definition | Slope | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of positive roof drainage?
The International Building Code (IBC) 2009 defines it in Roof Assemblies and Rooftop Structures as: “The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on positive roof drainage?
In this corpus the term is used across 4 chapters, led by Roof Assemblies and Rooftop Structures in the IBC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What is the definition of positive roof drainage?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Roof Assemblies and Rooftop Structures: “The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.” It is defined in IBC 2009, IRC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
Related pages
- Pool: Building Code Definition
Pool — IRC 2009 definition: Manufactured or field-constructed equipment designed to contain water on a permanent or semipermanent basis and used …
- Portable Fuel Cell Appliance: Building Code Definition
Portable Fuel Cell Appliance — IMC 2009 definition: A fuel cell generator of electricity, which is not fixed in place.
- Portable Outdoor Fireplace: Building Code Definition
Portable Outdoor Fireplace — IFC 2009 definition: A portable, outdoor, solid-fuel-burning fireplace that may be constructed of steel, concrete, clay or other noncombustible …
- Potable Water: Building Code Definition
Potable Water — IRC 2009 definition: Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects and …
- Powered Industrial Truck: Building Code Definition
Powered Industrial Truck — IFC 2009 definition: A forklift, tractor, platform lift truck or motorized hand truck powered by an electrical motor or …
- Precast Concrete: Building Code Definition
Precast Concrete — IRC 2009 definition: A structural concrete element cast elsewhere than its final position in the structure.