IBC 2006 Chapter 7 Fire-Resistive Construction (1 st part)

1. Session 12 | Codes | Gary Parker IBC 2006 Chapter 7 Fire-Resistive Construction (1st part)

2. Fire-Resistive Construction According to §702, fire-resistive rating is defined as the period of time ‘that a building element, component or assembly maintains the ability to confine a fire, continues to perform given structural function, or both’ as determined by tests or methods prescribed in §703. The time-rating in hours indicates how long a building material, element or assembly can maintain its structural integrity and/or heat transfer resistance in a fire, and correspond to the construction type designations in Chapter 6 of IBC.

3. Fire-Resistive Construction Whether passive or active, fire-resistive construction, has two primary purposes. The first is the protection of the building structure. Such protection is typically applied directly to structural members. The second is the separation of spaces to prevent the spread of fire or smoke within a building and the spread of fire between buildings. The protection of spaces addresses fire or smoke impacts on larger-scale building systems, such as floors, walls and ceilings as well as openings in these systems. According to §702, fire area is defined as the aggregate floor area enclosed and bounded by fire walls exterior walls fire-resistance-rated horizontal assemblies of a building.

4. Fire-Resistive Construction Exception to §703.2 allows exteriorbearingwall rating requirements to equal those for non-bearing walls when all factors such as fire separation and occupancy are considered. This exception recognizes that fire-resistance in exterior walls is concerned with stopping the spread of fire as well as protecting the structure. The code recognizes that there is no point in protecting the structure to a higher level than is required for the walls enclosing the space, since the governing criteria is the prevention of fire outside the building. With regard to the ability of structural members to expand or contract under fire conditions, the definition of ASTM E 119 assume that tested materials are not restrained. Hence, assemblies considered as restrained typically have a higher hourly rating with less application of fire protection and are thus attractive to use in design. The difficulty of designing and proving that assemblies are truly restrained very often outweighs any advantages gained in reducing the quantities of fire-protection materials used. Advise: follow the code sections assuming that all assemblies are unrestrained when determining the fire-resistance requirements.

5. Alternative Methods to Determining Fire Ratings §703.3 allows designers to use several other methods to ASTM E 119 to determine hourly ratings. Use ratings determined by Underwriters Lab or Factory Manual. Table 719 gives a list of protection measures that can be applied to different building elements. §720 allows the designer to calculate the fire-resistance of assemblies by combining various materials, hence giving a greater flexibility to meet the actual design conditions than the prescriptive set of assemblies of Table 719. §703.3 allows engineering analysis based on ASTM E 119 to be used to determine projected fire-resistance. This is based on extrapolations of test results to predict performance of systems without undergoing full-scale fire test. §703.4 recognizes that certain combinations of combustible and noncombustible materials may be considered as noncombustible if they meet noncombustibility test criteria.

6. Organization of Chapter 7 Code sections take the form of statements and exceptions. The code is organized to move from the exterior of the building to areas inside the building and then to the structure. The first set of assemblies can be thought of as planes, both vertical and horizontal, arranged around the structural system. These planes may be bearing walls and part of the structural system, or they may be curtain walls or interior partitions independent of the structure. There are various interrelated conditions that impact the fire-resistance requirements of the systems. Openings (and their protections) Location on the property Relationships of exterior walls facing each other (as in courts) Separation of interior spaces by fire walls Vertical circulation, vertical openings Protection of egress paths Smoke barriers Penetrations by utility systems Abutment of floor systems with curtain-wall systems Fire-resistive protection of structural systems.

7. Exterior Walls - Projections §704.2 governs the extent of allowable projections according to their relationship to property line. The combustibility of projections is governed by the wall construction type (which is related to height, areas and occupancy types). In cases when openings in the exterior walls are prohibited or opening protection is required by location on property, any combustible projection must be of 1-hour construction, even in unrated buildings. Projections include such elements as eave overhangs, cornices and balconies that extend beyond the floor area.

8. Exterior Walls – Projections Limited by 1st Method Exterior or interior property line Required fire-separation distance (L) §704.2 limits projections by the following two methods: First Method 1/3L maximum projection toward the property line, beyond the assumed vertical plane where protected openings are required as determined in accordance with Table 704.8

9. Exterior Walls – Projections Limited by 2nd Method Second Method 12” maximum projection into area where openings are prohibited, Required fire-separation distance Exterior or interior property line Assumed vertical plane as determined in accordance with Table 704.8

10. Exterior Walls – Multiple Buildings §704.3 assumes a property line between buildings or elements for multiple buildings on a site or configurations that create courts. No specification is given for the position of the line midway between buildings, hence the designer is free to locate the interior property line at any point as long as the wall protection requirements are met. The intent of this section is to prevent the spread of fire by radiant heating or convection.

11. Exterior Walls – Fire Resistance Ratings Two or more buildings on the same property may be treated as separated buildings with an assumed property line between. Note that distances need not be equal. If the buildings are treated as portions of a single building, the aggregate area of the building must be within the limits specified in Chapter 5. §704.3 assumes that the court walls of buildings more than one story in height have a property line between them. Opening protectives are not required in court walls if no more than 2 levels open onto the court, the aggregate area of the building (including the court) is within the allowable area, and the building in not a Group I occupancy.

12. Exterior Walls – Fire Resistance Ratings §704.5 specifies that exterior walls having a fire-separation distance > 5’ should be rated for exposure to fires from the inside. Exterior walls having a fire-separation distance <= 5’ must be rated for exposure from both sides.

13. Exterior Walls – Openings §704.7 contains detailed calculation for determining the fire-resistance rating of protected openings (Equation 7-1) §704.8 and Table 704.8 contain simpler calculations that relate the location on property to the percentage of wall openings and to whether the opening should be protected or not. Note that, §704.12 allows opening protection to be provided by an approved water-curtain exterior sprinkler along with a conventional interior fire-sprinkler system. This is an active measure that provides a substitution for passive protection. Additional passive or active fire-protection measures can also allow increases in the allowed area of openings.

14. Exterior Walls – Openings Equation 7-2 in §704.8 allows the designer to determine the amount of openings allowable given the relationship of protected versus unprotected openings under site and building conditions. A/a + Au/au <= 1 A = actual area of protected openings a = allowable area of protected openings as per Table 704.8 Au = actual area of unprotected openings au = allowable area of unprotected openings as per Table 704.8 §704.8.2 allows unlimited unprotected openings in the 1st floor of exterior walls if the exterior walls face a public street and have a fire-separation distance > 15’, or if they face an unoccupied spaces that is at least 30’ wide and has access from a street to a posted fire lane.

15. Exterior Walls – Vertical Separation of Openings §704.9 regulates the vertical relationship between openings. These restrictions do not apply for buildings with <3 stories in height and when fire sprinklers are provided. If openings in adjacent stories are <5’ of each other and the lower one is unprotected, §704.9 requires that they be separated vertically at least 3’ by an assembly of >= 1-hour rating. or by a flame barrier that extends horizontally >=30” beyond the exterior wall.

16. Exterior Walls – Vertical Exposure §704.10 requires the protection of openings in any wall of multiple buildings in the same property that extend above an adjacent roof. This protection can be provided in various ways: by distance, by opening protectives, or by protection of the roof framing and its supporting structure. Approved protectives are required for openings <15’ vertically above the roof of the adjacent structure. for a horizontal fire distance within 15’ of the adjacent structure.

17. Exterior Walls – Parapets §704.11 makes a general statement that parapets should be provided at exterior walls of buildings. Their purpose is to impede the spread of fire from one building to another by providing a barrier to fire and radiant heat transfer in case the fire breaks through the roof membrane. The exceptions that follow reduce or eliminate the need for parapets in case conditions are met. These exceptions become the code criteria rather than the general statement that parapets will always occur. Typically parapets are to extend >=30”above the roof and be on the same construction as the wall supporting them

18. Exterior Walls – Parapets - Exceptions No parapets are needed where: The wall satisfies the fire-separation distance criteria in accordance with Table 602 The building area is <1,000 sf on any floor The roof construction is entirely noncombustible or of at least 2-hour fire-resistive construction The roof framing is protected against the fire exposure from the inside (see next slide) In residential occupancies, a fire barrier is provided by sheathing the underside of the roof framing, or the roof sheathing is of noncombustible materials for 4’ back from the roof/wall intersection When >=25% of openings are allowed to be unprotected according to §704.8 due to the building’s location from a property line.

19. Exterior Walls – Parapets Parallel to exterior No openings are permitted within 5’ of fire-resistance-rated exterior walls in Groups R and M. A separation of 10’ is required for other occupancies. 1-hr rating roof/ceiling framing parallel to exterior wall 4’ minimum for Groups R and M; and 10’ for other occ. When not parallel to exterior walls, the entire span of roof/ceiling framing should be of >= 1-hr rated construction unrated wall due to fire-separation distance 1-hr rated exterior wall Not parallel to exterior

20. Fire Walls §702 defines a fire wall as a fire-resistance-rated wall which purpose is to restrict the spread of fire. A fire wall must extend continuously from the building foundation to and through the roof, and have sufficient structural stability to withstand collapse if collapse of construction on either side of the fire wall occurs. Structural Stability §705.2 requires that fire walls have a structural configuration that allows it to stay in place for the time required by the fire rating Materials §705.3 requires fire walls to be constructed of noncombustible materials, except Type V construction. Fire-Resistance Ratings §705.4 bases the required fire-resistance ratings of fire walls on occupancy. For most occupancies, fire walls are required to be 3-hr rating. Table 705.4 allows 2-hr ratings in Type II or V buildings for certain occupancies. In case a fire wall separates different occupancies, the most stringent requirements will apply. Horizontal Continuity §705.5 requires the fire walls to be continuous horizontally from exterior wall to exterior wall, and extend >=18” beyond the exterior surface of exterior walls.

21. Fire Walls §705.1 considers each portion of a building completely separated by one or more fire walls to be a separate building. Fire wall. If located on a property line and serving as a party wall, the fire wall is not allowed to have openings. §705.5 requires a fire wall to extend >= 18” beyond the exterior surface of exterior walls. There are exceptions based on the provision of additional fire-resistive construction at the exterior wall to provide a barrier heat and flame propagation.

22. Fire Walls – Exceptions to 18” Extension A fire wall may terminate at the interior surface of exterior sheathing, siding or other finish if fire-rated protection forms a “T” and extends a horizontal distance of at least 4’ on both sides of the fire wall. The fire-rated protection may be provided by exterior-wall construction having a rating of >= 1 hr, or by the use of noncombustible exterior sheathing, siding or other finish. §705.5 also allows a fire wall to terminate at the interior surface of noncombustible exterior sheathing if the building on each side of the fire wall is protected with an automatic sprinkler system.

23. Fire Walls – Horizontal Projections §705.5.2 requires fire walls to extend to the outer edge of horizontal projections, such as roof overhangs and balconies, that are within 4’ of the fire wall. There are 3 exceptions to this requirement

24. Fire Walls – Horizontal Projections - Exceptions (1) The extension is not required when horizontal projecting elements have no concealed spaces. The exterior wall behind and below such horizontal projections, however, must be of minimum 1-hr rated construction for a distance >= than the depth of projection on each side of the fire wall. In addition, any openings in the fire-rated exterior wall must have a fire-protection rating of >= ¾ hour.

25. Fire Walls – Horizontal Projections - Exceptions (2) If noncombustible horizontal projection have concealed spaces, a minimum 1-hr fire-resistance-rated wall must extend through the concealed spaces. As in the case (1), the projection must also be separated from the building by a minimum of 1-hr rated construction for a distance on each side of the fire wall equal to the depth of the projection. (3) If combustible horizontal projections have concealed spaces, the fire wall must extend through the concealed spaces to the outer edges of projections. The exterior wall behind and below the projections must be of a minimum 1-hr rating for a distance >= the depth of projection in each side of the fire wall.

26. Fire Walls – Vertical Continuity §705.6 requires that fire walls be continuous vertically from the building foundation to a point >= 30” above adjacent roofs. No horizontal offsets in the fire wall are permitted. The fire wall for a building located above a parking garage in accordance with §508.2 extends from the horizontal separation between the parking garage and the building above. Where the fire wall meets the roof construction, same principles for the “T” junctions between FW and exterior wall apply. It is best to presume that fire protection of roof construction extends to a minimum of 4’ on each side of the FW when framing is parallel to the wall and to the entire length of the span when framing is perpendicular to the wall.

27. Fire Walls – Vertical Continuity – Exceptions to 30” Above Not less than Class B roof covering The entire span of the roof framing perpendicular to a FW must have a 1-hr rating. Roof framing parallel to a FW must have >= 1-hr rating within 4’ of FW Roof framing must be supported by bearing walls or columns and beams with 1-hr rating No openings are permitted within 4’ of FW 2-hr FW Not less than Class B roof covering Noncombustible roof sheathing, deck or slab FRT wood permitted within 4’ of FW in Types III, IV and V construction No openings within 4’ from FW perpendicular parallel