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Uses and Limitations of
SB-2
Liz Hilfrich, P. Eng. CBCO
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Uses and Limitations of SB-2
SB-2 is one of two sources of fire
resistance ratings recognized by Part 3 of
the OBC, and one of three sources in Part
9 of the OBC
It is based on Appendix D to the NBC
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Uses and Limitations of SB-2
Because it is extremely generic, the
assigned times are more conservative
than either listed assemblies or SB-3
assemblies
It is also limited in the component
materials included
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Uses and Limitations of SB-2
There are sections for
Masonry and Concrete Walls
Reinforced and Prestressed Concrete Floor
and Roof Slabs
Wood and Steel Framed Walls, Floors and
Roofs
Solid Wood Walls, Floors and Roofs
Solid Plaster Partitions
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Uses and Limitations of SB-2
There are sections for
Protected Steel Columns
Individually Protected Steel Beams
Reinforced Concrete Columns
Reinforced Concrete Beams
Pre-stressed Concrete Beams
Glued-Laminated Timber Beams and
Columns
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Uses and Limitations of SB-2
It also contains information with respect to:
The flame spread rating and smoke
developed classification of various common
construction materials
Non-combustibility testing
Protection of Openings
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Uses and Limitations of SB-2
Let’s start by looking at the provisions for
masonry and concrete walls, both unreinforced
and reinforced
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Uses and Limitations of SB-2
For masonry and concrete, SB-2 uses an
“equivalent thickness” measure
The required equivalent thickness will depend
on the type of concrete used and the desired
fire rating
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Uses and Limitations of SB-2
Section 1.6 provides the methods of
determining the equivalent thickness of
brick, block, hollow core pre-cast concrete,
ribbed or undulating concrete panels and
tapered concrete panels
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Uses and Limitations of SB-2
A plaster finish and gypsum wall board will
also contribute, with limitations, to the
equivalent thickness
The time contribution of these materials is
different for the fire exposed and non-fire
exposed sides of the assembly
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Uses and Limitations of SB-2
The contribution of finishes on the fire exposed
side of the assembly is determined from Tables
2.3.4.A. or 2.3.4.B.
On the non-fire exposed side, Table 1.7.1.
provides a multiplying factor varying from 0.5 to
1.75 times depending on the type of plaster and
the type of masonry or concrete
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
Table 2.1.1. lists the minimum required
equivalent thickness for the various
masonry and concrete types for fire
resistance ratings from 30 minutes to 4
hours
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
Ratings for reinforced & prestressed
concrete floor and roof slabs are also
determined using thickness
measurements for both the concrete slab
and the concrete cover over the
reinforcement
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Uses and Limitations of SB-2
Specific provisions are included for
composite slabs composed of two layers
of different types of concrete, or of
concrete topped with gypsum wallboard,
portland cement or terrazzo
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Uses and Limitations of SB-2
Plaster finishes on the underside of
reinforced concrete floors provide a time
contribution on the same basis as for
concrete or masonry walls.
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Uses and Limitations of SB-2
Under SB-2 the maximum attainable fire
resistance rating for wood and steel framing is
90 minutes.
All of the times given in Article 2.3.4. are
contributions to a total rating and are not
intended to be treated as a rating of the
individual materials by themselves.
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Uses and Limitations of SB-2
Interior walls need a membrane on both
sides
Exterior walls need exterior sheathing and
cladding
Floor assemblies need subflooring and
finished flooring
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Uses and Limitations of SB-2
Wallboard membranes are permitted to be
installed in multiple layers only as listed in
Table 2.3.4.A. (Double 12.7 mm Type X
gypsum wallboard).
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Uses and Limitations of SB-2
When calculating the fire resistance rating, a
time assignment is included:
For the membrane or finish only on the fire
side, not on the unexposed side
For the framing members
For any additional protection
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
There are specific provisions included for
how to measure a plaster thickness,
framing members, fastening of
membranes and permitted openings in
ceiling membranes of assemblies
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Uses and Limitations of SB-2
SB-2 Article 2.3.12. contains provisions for
determining a rating of up to 60 minutes
based only on a ceiling membrane, not on
the entire assembly
This option prohibits any openings in the
ceiling membrane.
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Uses and Limitations of SB-2
Section 2.3.14. lists the requirements for
untested wired glass assemblies used as
a closure in a fire separation as permitted
by Sentence 3.1.8.14.(2) of the OBC
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Uses and Limitations of SB-2
Section 2.4 provides minimum thickness
information for solid wood walls, floors and
roofs for fire resistance rating for up to 90
minutes
Section 2.5 deals with solid plaster
partitions with fire resistance ratings of up
to 4 hours
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Uses and Limitations of SB-2
Protection of steel columns is addressed
in many forms, including the use of
concrete, block, brick, clay tile, plaster,
sheet steel and insulation, and gypsum
wallboard on the exterior of the column
Concrete filled hollow steel columns are
also included
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Uses and Limitations of SB-2
Let’s have a closer look at Table 2.6.1.F.
for drywall protection of a column
This requires that you know the M/D ratio for the
column. This information is available in AISC
and/or CISC design manuals
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Uses and Limitations of SB-2
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Uses and Limitations of SB-2
Where a steel beam is exposed on three
side, methods of protecting the beam are
provided in Section 2.7. of SB-2
The methods listed are unfortunately
limited to concrete and plaster, and do not
include any gypsum board options
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Uses and Limitations of SB-2
The fire resistance rating determination for
reinforced concrete columns is dependant
of the type of concrete, the effective length
of the column and the cross sectional area
of reinforcing
A plaster finish can contribute to the cover
over the reinforcing, but not to the required
size of the column itself
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Uses and Limitations of SB-2
For reinforced and pre-stressed concrete
beams, the main factors are the type of
concrete and the amount of concrete
cover protecting the reinforcing
For reinforced concrete beams, there are
limitations to the maximum rating based
on the width of the beam
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Uses and Limitations of SB-2
Lastly, Section 2.11. provides the formulas
to be used establish the fire resistant
ratings for glue-laminated timber beams
and columns
It is most likely intended to be used for fire
resistance ratings greater than those
provided by the heavy timber construction
provisions
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Uses and Limitations of SB-2
There are separate equations for beams
and columns exposed to fire on three or
four sides
Some structural information is required to
complete the calculations
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Uses and Limitations of SB-2
Questions?