Fire Blocking vs. Draft Stopping: Definitions and Application Requirements According to the International Building Code
Managing the spread of fire and smoke is a critical aspect of ensuring the safety of a building’s occupants. Two critical requirements for achieving this goal that are often confusing for designers are fire blocking and draft stopping. Part of the reason for this confusion is that the application of these requirements is similar:
- Each of these are only required for combustible construction.
- Furthermore, for combustible construction, they are only required in concealed spaces (i.e. within stud walls, floor/ceiling assemblies, attics, mechanical chases, etc.).
While often confused for one-another, they are different requirements and serve distinct purposes. Understanding these differences is crucial for architects, builders, and safety inspectors.
How does the code define these terms?
As a first step, let’s look at how the building code (780 CMR) defines these terms in Section 202:
- Fireblocking: Building materials or materials approved for use as fireblocking, installed to resist the free passage of flame to other areas of the building through concealed spaces.
- Draftstop: A material, device or construction installed to restrict the movement of air within open spaces of concealed areas of building components such as crawl spaces, floor/ceiling assemblies, roof/ceiling assemblies and attics.
Within these definitions, we see that fireblocking is specific to the passage of flame while draftstopping is installed to restrict the movement of air. This is the critical distinction and drives where and how these materials are installed.
Fire Blocking: Application Requirements
Fire blocking is essential in maintaining the compartmentalization within a building, preventing the passage of flame from one area to another. Common materials used for fire blocking include nominal 2-inch thick lumber, 0.375-inch plywood or particle board, ½-inch drywall, densely packed batts or blankets of mineral wool, etc. Examples of fire blocking installations are:
- Top and bottom of stud walls to limit concealed spaces to 10 feet, vertically.:
- Intersections between concealed vertical and horizontal spaces, such as where walls meet floors or ceilings.
- Stairways at the top and bottom of the run
- Ceiling and floor penetrations of chimneys, ducts, pipes, etc.
- Exterior wall covering and furring
Draft Stopping: Application Requirements
Common materials used for draft stopping include gypsum board, plywood, and mineral wool insulation, depending on the specific application and building code requirements. Draft stopping is required in:
- Attics and Concealed Roof Spaces: In buildings with large attics or concealed roof spaces, draft stopping must be installed to divide the area into smaller compartments. Generally, it must be provided to divide concealed areas into no greater than 3,000 sf.
- Floor-Ceiling Assemblies: In wood-frame construction, draft stopping is required in floor-ceiling assemblies to divide the concealed spaces into smaller compartments. Generally, it must be provided to divide concealed areas into no greater than 1,000 sf.
These requirements may differ for your specific project based on the size of any residential unit and/or whether the space is sprinklered.
Key Differences Between Fire Blocking and Draft Stopping
While both fire blocking and draft stopping aim to control the spread of fire and smoke within a building, they differ in several key aspects:
| Aspect | Fire Stopping | Draft Stopping |
| Primary Purpose | Prevents vertical and horizontal fire spread within concealed spaces, especially in wall assemblies. | Restricts horizontal movement of fire and smoke within large, concealed spaces like attics and floor-ceiling assemblies. |
| Application Areas | Concealed wall spaces, interconnections between floors and walls, around openings, under stairs. | Large horizontal spaces such as attics, crawl spaces, and floor-ceiling assemblies. |
| Area Coverage | Focuses on interrupting smaller concealed cavities and spaces. | Subdivides large areas into specified maximum compartment sizes (e.g., 1,000 or 3,000 square feet). |
| Materials Used | Requires materials that can resist fire spread, such as lumber, gypsum board, mineral wool, and fire-retardant foams. | Materials primarily aim to restrict air movement, including gypsum board, wood structural panels, and mineral wool insulation. |
In conclusion, while fire stopping and draft stopping may seem similar, they address different aspects of fire safety. Understanding their differences and following the IBC guidelines for their application is essential for anyone involved in the construction, renovation, or inspection of buildings. By doing so, we contribute to creating safer environments by limiting the spread of smoke and fire.
If you have any questions related to how these requirements apply to your project, please contact us at support@jigsawlifesafety.com.
