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BCC Ruling No. 00-05-737

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BUILDING CODE COMMISSION DECISION ON B.C.C. #00-05-737

IN THE MATTER OF Subsection 24(1) of the Building Code Act, 1992.

AND IN THE MATTER OF Sentence 3.1.5.3.(2) of Regulation 403, as amended by O. Reg. 22/98, 102/98, 122/98, 152/99, 278/99, 593/99 and 597/99 (the "Ontario Building Code").

AND IN THE MATTER OF an application by Mr. Christopher Boyd, Project Architect, Rebanks Architects Inc., Toronto, Ontario, for the resolution of a dispute with Mr. Terry Willing, Chief Building Official, City of Kingston, Ontario, to determine whether the proposed roof assembly that includes fire-retardant plywood sheathing on Z-girts with a 25 mm air space and RSI 3.25 mineral fibre insulation mounted on a 38 mm decking provides sufficiency of compliance with Sentence 3.1.5.3.(2) of the Ontario Building Code at the Loblaws Supermarket, Princess Street and Bath Road, Kingston, Ontario.


APPLICANT
Mr. Christopher Boyd, Project Architect
Rebanks Architects Inc.
Toronto, Ontario

RESPONDENT

Mr. Terry Willing
Chief Building Official
City of Kingston

PANEL
Mr. Kenneth Peaker (Chair-Designate)
Mr. John Guthrie
Mr. Robert De Berardis

PLACE
Toronto, Ontario

DATE OF HEARING
February 3, 2000

DATE OF RULING
February 3, 2000

APPEARANCES
Mr. Randal Brown, President/Consulting Engineer
Randal Brown & Associates Ltd.
Toronto, Ontario
Agent for the Applicant

RULING

  1. The Applicant

Mr. Christopher Boyd, Project Architect, Rebanks Architects Inc., Toronto, Ontario, has applied for a building permit under the Building Code Act, 1992, to construct a new Loblaws Supermarket, at the intersection of Princess Street and Bath Road, Kingston, Ontario.

  1. Description of Constrution

The Applicant is proposing to construct an addition to an existing mall that will serve as a Loblaws supermarket. The mall is 23 180 m2 in building area excluding the Sears store, which is to be demolished and will be replaced by the proposed Loblaws facility. The addition is described as a two storey, non-combustible structure with a building area of 7,432 m2, that is classified as having a Group E - (retail) mercantile major occupancy. The building is to be equipped with a sprinkler system and a fire alarm system, but not a standpipe and hose system.

The roof assembly, as proposed by the Applicant, consists of Class A shingles and roofing felt nailed to 13 mm thick exterior grade fire-retardant treated plywood sheathing that is fastened to 18 gauge galvanized Z-shaped metal girts (spaced at 24 in. on centres) which are, in turn, mounted on 38 mm thick fluted metal decking on steel framing. Directly underneath the plywood sheathing will be a 25 mm air space below which will be (in descending order in the roof assembly) RSI 3.25 mineral fibre insulation sitting on 6 mm poly vapour barrier that rests directly on the metal decking. The majority of the proposed roof will be at an angle of approximately 300 to the horizontal.

The construction in dispute involves the intended use of combustible plywood sheathing in the proposed roof assembly of a building that is required to be constructed of non-combustible construction.

  1. Dispute

The issue at dispute between the Applicant and Respondent is whether the proposed roof assembly that includes fire-retardant treated plywood sheathing intended for a building that is required to be noncombustible according to Article 3.2.2.57. provides sufficiency of compliance with Sentence 3.1.5.3.(2) of the Ontario Building Code. This provision allows a combustible roof under certain conditions but only if it is constructed above a concrete roof deck. The Applicant's proposed roof deck, however, is steel not concrete. Further, the OBC does not set out specific conditions which would permit a combustible roof over a metal roof deck.

  1. Provision of the Building Code

Sentence 3.1.5.3.(2) - Combustible Roofing Materials

    1. ,
    2. Combustible roof sheathing and roof sheathing supports installed above a concrete deck are permitted on a building required to be of noncombustible construction provided:

a. the concrete deck is not less than 50 mm (2 in) thick;

b. the height of the roof space above the deck is not more than 1000 mm (3 ft 3 in);

c. the roof space is divided into compartments by fire stops in conformance with Article 3.1.11.5.;

d. openings through the concrete deck other than for non-combustible roof drains and plumbing piping are protected by masonry or concrete shafts:

i. constructed as fire separations having a fire-resistance rating not less than 1 h; and

ii. extending from the concrete deck to not less than 150 mm (57/8 in) above the adjacent roof sheathing;

e. the perimeter of the roof is protected by a noncombustible parapet extending from the concrete deck to not less than 150 mm (57/8 in) above the adjacent sheathing; and

f. except as permitted by Clause (d), the roof space does not contain any building services.

  1. Applicant's Position

The Agent for the Applicant submitted that the proposed roof assembly which includes a fire-retardant plywood sheathing and rigid fibreglass insulation provides an equivalent level of safety to that intended in the OBC. As he argued, Sentence 3.1.5.11.(5) and Clause 3.1.14.2.(2)(b) allow the use of foam plastic insulation above a roof deck if the building is sprinklered. In his view, the plywood sheathing is less hazardous than the permitted foam plastic insulation because it has been treated with a fire-retardant thereby giving it a maximum flame-spread rating of 25. Moreover, since the proposed air space in the assembly is small, at 25 mm or less, flames will not propagate throughout such a restricted space regardless of the flame-spread rating, the Agent argued. He indicated that there were test results on wall assemblies to support this position.

The Applicant added that the treated plywood only chars, it does not propagate flame. Only continuous exposure to flame will cause the material to burn, he stated. Since the material is located between Class A shingles and metal roof decking it would therefore not be readily exposed to any exterior source of flame.

As well, since the building is being sprinklered (which allows the roof assembly to be unrated) the resulting ceiling temperature of 2950C combined with an ambient temperature of 220C for a total temperature of 3170C allows the use of the foamed plastic insulation in the roof assembly. The same principle of sprinkler protection, the Agent asserted, could also apply to the combustible plywood sheathing proposed for the roof assembly. As he argued, wood not treated with fire retardant protection has an ignition point of between 3300C to 6000C, but since this wood is treated it would not ignite unless exposed to a much higher temperature. (The proposed plywood is treated throughout, not just surface coated.) In other words, in the event of a fire the sprinkler system would actuate and keep the temperature in the ceiling and roof areas low enough that the combustible elements, specifically the plywood, would not ignite.

The Agent also argued that using treated plywood as the nailing surface has advantages over the permitted combustible cant strips. Plywood creates fewer voids in the roof assembly than the wood strips. As well, the untreated wood strips, if used, add significantly to the allowable combustible load in a roof assembly.

Lastly, the Agent noted that this exact same issue had been addressed in a previous BCC ruling (No. 99-57-713) also in Kingston. He indicated that in the earlier ruling, the Commission found that the proposed roof assembly with fire-retardant treated plywood provided sufficiency of compliance with Sentence 3.1.5.3.(2) of the Code. He stated that he had asked that the municipality consider the present dispute with regard to the previous BCC ruling and approve the proposed roof assembly using their powers of "equivalency" in Section 2.7. of the Code. They refused.

For these reasons, the Agent argued that the proposed roof assembly provides sufficiency of compliance with Sentence 3.1.5.3.(2) of the OBC.

  1. Respondent's Position

The Respondent chose not to attend the hearing. The Commission therefore relied upon his written submission only.

The Respondent stated that the proposed use of combustible plywood, albeit treated with a fire-retardant, in a roof assembly of a building required to be of non-combustible construction does not provide sufficiency of compliance with Sentence 3.1.5.3.(2) of the OBC. He noted that Sentence 3.1.5.3.(2) specifically permits a combustible roof sheathing under certain conditions but only if the roof deck is constructed of concrete. He indicated, however, that in the subject dispute the decking is to be steel, not concrete. As a result, he argued that the proposal does not comply with OBC Sentence 3.1.5.3.(2).

  1. Commission Ruling

It is the decision of the Building Code Commission that the proposed roof assembly that includes fire-retardant plywood sheathing on Z-girts with a 25 mm air space and RSI 3.25 mineral fibre insulation mounted on a 38 mm decking provides sufficiency of compliance with Sentence 3.1.5.3.(2) of the Ontario Building Code at the Loblaws supermarket located at Princess Street and Bath Road, Kingston, Ontario.

  1. Reasons

(i) Class A shingles will be used;
(ii) For Trent treated plywood, when the flame source is removed, the treated plywood ceases to char and since it will not support combustion the flame will not spread;
(iii) The treated lumber is considered equal or better than the permitted combustible nailing strips and foam insulation;
(iv) Mineral fibre insulation will be used.


Dated at Toronto this 3rd day in the month of February, in the year 2000, for application number 2000-02.





____________________________

Mr. Kenneth Peaker, Chair-Designate





_______________________

Mr. John Guthrie





__________________________

Mr. Robert De Berardis