Canada Builds

Fire Protection

Part 9 of the Ontario Building Code describes measures for Fire Protection in Section 9.10. In terms of finding information on any question or problem regarding Fire protection, remember ‘9.10’. This will be the starting point to find your answers.

There are three distinct terms to remember when studying Fire Protection:

 

  1. Fire Separation
  2. Fire Resistance Rating
  3. Fire Protection Rating

 

Fire protection requirements in Part 9.10 determine the type of construction (combustible or non combustible), fire separations, fire resistance ratings, closures and fire protection equipment (fire and smoke alarms and smoke detectors) for all parts of the building except exits (covered under Section 9.9.4.)

Fire separation

A Fire Separation is a construction assembly that acts as a barrier against the spread of fire and smoke.

Fire-protection rating

Fire Protection Rating means the time in hours or fraction thereof that a closure will withstand the passage of flame when exposed to fire.

Fire resistance ratings (FRR)

Fire Resistance Rating means the time in hours or fraction thereof that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire.

 

Determining the required FRR for the floors and roofs depends on a building’s occupancy and height. Building area is not identified in Part 9 as a determinant for FRR of floors and roofs. Part 3 (large buildings) does require the inclusion of building area as a determining factor for FRR. The determination of required FRR for floors and Roofs is an important consideration to be made at an early stage in the design process. Considering the proportionately large planar area of the floors and roofs in a building, the construction requirements for a 1 hour floor as opposed to a 1.5 hour floor can be significant. Another layer of drywall or the addition of a sprinkler system can have a huge bearing on cost – not to mention design intent.

Table 9.10.8.1.

Forming part of sentence 9.10.8.1.(1)

Fire Resistance Ratings for Structural Members and Assemblies

 

Major Occupancy

Maximum

Minimum Fire Resistance Rating by Building Element, min

 

Building

Height

Storeys

Floors Except Floors over Crawl Spaces

Mezzanine

Floors

Roofs

Residential(Group C)

3

45

45

All other occupancies

2

3

45

45

45

45

Column 1

2

3

4

5

 

When reading Table 9.10.8.1. above, it becomes evident that the separation between floors for Part 9 buildings will usually be 45 minutes or nothing. The exceptions to this general rule are listed in a few places such as the following articles - 9.10.8.8., 9.10.9.11., 9.10.9.14., 9.10.9.16. and 9.10.9.17. The greater the rating of table 9.10.8.1 or these articles shall apply.

Read 9.10.9.11 - As a general rule, residential occupancies need to be separated from other occupancies with a one hour rating. If the adjoining occupancy is mercantile (Group E) or medium hazard industrial (F2), the fire separation will require a fire resistance rating of 2 hours.

9.10.9.11.(3) states that the separation need only be 1 hr if there are no more than 2 residential suites contained with the Group E or F2 occupancy.

Consider the following example: A three storey building with a hobby store on the ground floor and two residential apartments above. Using Table 9.10.8.1., a three storey group E building would require a 45 minute floor. Reading on however to article 9.10.9.11., we discover that residential occupancies need to be separated from Group E occupancies with a fire separation having an FRR of 1 hr. The floor between the hobby shop and the apartment suite above would require a 1 hr. rating.

 

Figure 1    3 storey building

Supplementary Standards

SB-2 is a portion of the supplementary guidelines that describes prescriptive methods to add up various portions of wall or floor assemblies to achieve an acceptable FRR. This Section is suitable for use with either a Part 3 or Part 9 building. SG-8 is a series of tables giving FRR and STC information for wall and floor assemblies. Generally, SG-8 is the first place one would look to derive FRR and STC requirements for a wall. If you find your wall or floor type in this section and it meets the required FRR and STC requirements then the minimum standard required by the code has been satisfied. SB-2 is used to determine assemblies that may not be found in SB-8. SB-2 is also required to be used for Part 3 buildings. If you look at the beginning sentence in SG-8 there is an explicit reference to the scope of SG-8 with regards to Part 9 buildings. SB-2 may be referenced as a question in the exam thereby forcing you to use this section to find an answer. What follows is a description of these two portions of the Supplementary guidelines with examples showing how the various articles and tables are employed

Equivalent Thickness

SB-2 1.6 describes the method of calculating what is referred to as ‘equivalent thickness’ when determining the FRR of hollow core concrete or masonry units. For units that contain cores or voids, the tables refer to the equivalent thickness determined in conformance with various requirements. A ‘unit’ that contains a core or void might be a typical hollow core concrete block. An 8” concrete block is used in the following example to determine ‘equivalent thickness’. Read through the sentences of Section 1.6 while referring to this example.

 

Figure 2                Excel worksheet to calculate equivalent thickness

 

Note: this chart is developed as an excel spreadsheet and can be used readily to identify equivalent thicknesses for other shapes. The block drawing is a cad file with the area calculation for the voids and solids derived automatically using the ‘bpoly’ command in AutoCAD. This is the information that is used to assess the Fire Resistance Rating of a hollow core concrete or masonry unit. Read Table SB 2.1.1. for references to ‘equivalent thickness’.

Party Walls

As a general rule, Firewalls need to be constructed using masonry. The exception to this rule is for dwelling units where there is no dwelling unit above another. Read an excerpt from the MMAH website for an interpretation on the issue of party walls between dwelling units. Consider the following question and Branch opinion regarding party walls for dwelling units

 

BRANCH OPINION

9.10.11.1 (February 28, 1996)

QUESTION:

Does a party wall on a property line between two dwelling units that is required to have a 1 hour fire-resistance rating and be continuous from the top of the footings to the underside of the roof deck need to extend to the upper roof deck if one of the roofs decks is above the other in elevation.

DISCUSSION:

Normally a party wall on a property line has to be constructed as a firewall (Article 9.10.11.1.).

Article 9.10.11.2. Firewalls not required is an exemption to this general requirement for party walls between residential buildings in which there is no dwelling unit above another dwelling unit.

This exemption allows for a continuous 1 hour fire-resistance rated fire separation to be constructed between the units from the top of the footings to the underside of the roof deck.

However, if the adjoining dwelling units do not have the same roof deck level, the fire separation must be continuous to the underside of the upper roof deck.

 

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