In construction, a firewall is a fire-resistance rated wall assembly intended to slow the spread of fire from one side to the other, and are certification listed. Firewalls subdivide a building into separate fire areas, and are located in accordance with the locally applicable building code. Firewalls are a portion of a building's passive fire protection systems.


There are two main classifications of fire walls: fire partitions, and true fire walls. To the layperson, the common use of language typically includes both when referring to a firewall unless distinguishing between them is necessary.

  • A fire wall is a wall separating buildings or subdividing a building to prevent the spread of fire and having a fire resistance rating and structural stability. .

There is a further sub-classification of fire walls. A High Challenge Fire Wall is a wall used to separate buildings or subdivide a building with high fire challenge occupancies, having enhanced fire resistance ratings and enhanced appurtenance protection to prevent the spread of fire, and having structural stability.

Portions of structures that are subdivided by fire walls are permitted to be considered separate buildings, in that fire walls have sufficient structural stability to maintain the integrity of the wall in the event of the collapse of the building construction on either side of the wall.

  • A fire barrier wall, also referred to as a fire partition, is a fire rated wall assembly which is not a fire wall. Typically, the main differences is that a fire barrier wall is not structurally stable, and does not extend through the roof, or to the underside of the floor above.

Fire barrier walls are continuous from an exterior wall to an exterior wall, or from a floor below to a floor or roof above, or from one fire barrier wall to another fire barrier wall, fire wall, or high challenge fire wall having a fire resistance rating of at least equal rating as required for the fire barrier wall. They are continuous through all concealed spaces (e.g., above a ceiling), but are not required to extend through concealed spaces if the construction assembly forming the bottom of the space has a fire resistance rating at least equal of the fire barrier wall.


  • Fire rating - Fire walls are constructed in such a way as to achieve a code-determined fire-resistance rating, thus forming part of a fire compartment's passive fire protection.
  • Design loads – Fire wall must withstand a minimum 5 lb./sq.ft., and additional seismic loads.

Germany includes repeated impact force testing upon new fire wall systems. Other codes require impact resistance on a performance basis

  • Firewalls typically extend through the roof and terminate at a code-determined distance above it. They are usually finished off on the top with flashing (sheet metal cap) for protection against the elements.
  • Materials - Firewalls in North America are usually made of concrete block or reinforced concrete. Fire barrier walls are typically constructed of gypsum board partitions.
  • Penetrations – Penetrations through fire walls, such as for pipes and cables, must be protected with a firestop assembly to prevent the spread of fire through the wall at this point. Fire walls must not be penetrated such that the wall is structurally weakened in a fire and could collapse.
  • Openings – Openings in Fire walls, such as doors and windows, must be fire rated as fire door assemblies and fire window assemblies.

Performance based design

Modern fire-testing methods have shown that the traditional concrete or masonry firewall is not always required to provide the degree of safety required of a firewall. For example, the use of a 4-hour fire-rated concrete or masonry firewall to separate buildings constructed of highly combustible wood framing might be unnecessary, since it could be unlikely that the building on either side would actually burn for more than 2 hours without collapsing.

Alternate materials

Since 2000, the International Building Code (Section 705.3), widely adopted in the United States, has permitted the use of firewalls constructed of non-combustible construction other than concrete or masonry. This departure from traditional methods and techniques has proven to be controversial, especially for more conservative building code officials. Another major critic has been the concrete masonry industry, that sees its niche in the construction industry affected by the shift to other firewall materials. This controversy has resulted in a large number of local authorities adopting amendments to the IBC that restrict the use of firewalls built of other than concrete and masonry within their jurisdictions.


The most novel, lightweight approach to building firewalls that pass the tough German DIN4102 test as well as North American test regimes including the hose-stream test includes the use of mechanically bonded sheet metal and concrete composite boards ("DuraSteel"). Even though this is a much lighter and fast construction method than the norm, it meets code because it contains a small amount of concrete, albeit cellulose reinforced, with a mostly sacrificial exposed side, as its hydrates are quickly spent and the fibres are ineffective in holding together the loose powder that is left over from what used to be integral concrete, after even small fire exposures. As a system, however, with a front and a back on each side of the framework, it works very well under any test regime the world over.

Firewalls outside of building construction

Firewalls are also regularly found in aircraft and in specially prepared cars for compartmentalisation and competition use. For example, a typical conversion of a production car for rallying will include a metal firewall which seals the fuel tank off from the interior of the vehicle. In the event of an accident, resulting in fuel spillage, the firewall can prevent burning fuel from entering the passenger compartment, where it could cause serious injury or death. In regular stock cars, the firewall separates the engine compartment from the cabin and can, at times, contain fibreglass insulation. Automotive firewalls have to be fitted so that they form a complete seal. Usually this is done by bonding the sheet metal to the bodywork using fibreglass resin.

The term firewall is also commonly used by automotive mechanics to refer to the barrier between the passenger and engine compartments of any vehicle.


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