The Canadian Building Codes allow a couple of methods for determining fire-resistance ratings of assemblies, from Article 3.1.7.1.:

• Tests conducted in conformance with CAN/ULC-S101 (usually demonstrated through a UL or other listing)
• Appendix D of the Building Code

It is important to note that the fire & sound resistance tables from Part 9 (Tables 9.10.3.1.-A and 9.10.3.1.-B) cannot be used in Part 3 buildings for assigning fire-resistance ratings. They can be applied for assigning Sound Transmission Class only in Part 3 buildings.

Designers who are used to applying the Part 9 tables for assigning fire-resistance ratings sometimes have difficulties when trying working on Part 3 buildings. This post provides a high level overview of the component additive method (CAM) for wood and steel frame walls, floor and roofs from D-2.3 of Appendix D in the Building Code and some common mistakes.

The fire & sound resistance tables from Part 9 cannot be used in Part 3 buildings for assigning fire-resistance ratings.

Appendix D or a Listing?

The main advantage of using Appendix D for assigning fire-resistance ratings over a listing is that Appendix D uses generic materials, while most listings reference specific proprietary products. When applying Appendix D, Type X gypsum board means any product that meets the special fire-resistant board requirements from CAN/CSA-A82.27-M or ASTM C1396/C1396M. Understanding the details of these standards are most likely not important for applying Appendix D, but the gypsum board product sheets will indicate if the product meets Type X based on one of these standards if there is any uncertainty.

Listings, in contrast, often reference specific products from various manufacturers. Since products are generally not specified on architectural drawings, this can lead to discrepancies between design and installation, which could void the listing.

How to Use Component Additive Method

Fire-resistance ratings using the CAM are assigned by adding times assigned to each component in the assembly:

• Membranes on fire exposed side (Table D-2.3.4.-A for walls, Table D-2.3.4.-B for floors)
• Framing members (Table D-2.3.4.-E for walls, Table D-2.3.4.-F for floors and roofs)
• Additional protection from Table D-2.3.4.-G (e.g. insulation, concrete topping)

It is important to note that interior partitions require a membrane on both sides, but the time for only one side (the fire exposed side) is considered. For asymmetrical assemblies, the lowest time between the membrane(s) on either side of the framing members needs to be used.

Framing members must comply with D-2.3.6, which includes minimum size requirements (e.g min. 2×4 for wood studs, min. 2×8 for solid wood joists).

Keep in Mind…

Here are a few notes to remember before you try to define an assembly using the CAM:

1. Maximum 90 min fire-resistance rating

The CAM method in D-2.3. of Appendix D can only be used to assign ratings up to 90 min. If you require a rating over 90 min, you will either have to use a listing or a different type of assembly (not wood or steel frame). Appendix D can assign ratings in excess of 90 min for other types of assemblies, such as concrete walls or floors,

2. Fire-resistance rating cannot be increased by adding additional membrane layers

Multiple layers of membranes can be used in assemblies; however, the rating assigned to the assembly would be based on a single layer only, unless the table being applied specifically mentions multiple layers. For example, Table D-2.3.4.-A (see below) assigns a 50 min rating for double 12.7 mm Type X in a loadbearing assembly. Two layers of 15.9 mm Type X can be used; however, the rating assigned to the membrane would only be 40 min.

It is common to provide additional layers of drywall to increase the STC of an assembly, or plywood for structural purposes. Both are acceptable provided the membrane fastening requirements in D-2.3.9. are still met and no additional time for the additional layers are assigned.

3. Times assigned are not the fire-resistance ratings of individual components

The CAM assumes a full assembly with certain constraints. For interior fire separations, this would consist of a membrane on each side of framing members. For floor assemblies, the assembly would consist of a membrane on the underside of framing members and a subfloor on top. If any of these components is omitted, no fire-resistance rating can be assigned.

The times assigned to membranes in the CAM are not the same as “finish ratings” sometimes cited in listings. The times assigned to membranes are based primarily on their ability to remain in place during fire tests. A fire-resistance rating, however, also includes a temperature rise limitation criteria. The temperature rise criteria is not accounted for in the times assigned to components in Appendix D, as it relies upon the entire assembly to meet the criteria. Finish ratings provided on listings account for the temperature rise criteria and can be considered as the fire-resistance rating provided by the finish/membrane only in an assembly.