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BCC Ruling No. 99-57-713

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BUILDING CODE COMMISSION DECISION ON B.C.C. #99-57-713

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

AND IN THE MATTER OF Sentence 3.1.5.3.(1) and (2) of Regulation 403, as amended by O. Reg. 22/98, 102/98, 122/98, 152/99 and 278/99 (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 R19 fibreglass batt insulation mounted on a 38 mm metal decking provides sufficiency of compliance with Sentence 3.1.5.3.(1) and (2) of the Ontario Building Code at the Loblaws Supermarket, 1048 Midland Avenue, 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. Fred Barkhouse
Mr. John Guthrie

PLACE

Toronto, Ontario

DATE OF HEARING

August 26, 1999

DATE OF RULING

August 26, 1999

APPEARANCES

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

Mr. Ted Marecak
Building Official
City of Kingston
Designate for the Respondent

RULING

  1. The Applicant

Mr. Christopher Boyd, Project Architect, Rebanks Architects Inc., Toronto, Ontario has received a building permit under the Building Code Act, 1992 to construct a new Loblaws Supermarket at 1048 Midland Avenue, Kingston, Ontario.

  1. Description of Construction

The Applicant is currently constructing a two storey, noncombustible structure with a building area of 7,504 m2, that is classified as having a Group E - (retail) mercantile major occupancy. The building is considered to face one street for fire fighting purposes and is 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 are 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. Below the plywood sheathing is to be a 25 mm air space below which will be found R19 fibreglass insulation sitting on top of 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 30 degrees 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 noncombustible 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 Sentences 3.1.5.3.(1) and (2) of the Ontario Building Code. Sentence (1) allows a combustible roof covering on a noncombustible building provided that the covering has an A, B or C classification as determined in conformance with CAN/ULC-S107-M87, "Standard Method of Fire Tests for Roof Coverings". The Applicant's proposed roof covering has an A classification. Sentence (2) allows a noncombustible roof under certain conditions if it is constructed above a concrete roof deck. The Applicant's proposed roof deck, however, is steel not concrete.

  1. Provisions of the Ontario Building Code

Sentence 3.1.5.3.(1) and (2) Combustible Roofing Materials

(1) Combustible roof covering which has an A, B, or C classification determined in conformance with Subsection 3.1.15. Is permitted on a building required to be of noncombustible construction.

(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 1,000 mm (3ft 3in),
(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 noncombustible 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 (5 7/8 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 (5 7/8) above the adjacent sheathing, and
(f) exxcept as permitted by Clause (d), the roof space does not contain any building services.

  1. Applicant's Position

The Applicant submitted that the proposed roof assembly which includes a fire-retardant plywood sheathing and fibreglass batt 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 Applicant argued. He indicated that there were test results on wall assemblies to support this position.

As well, since the building is being sprinklered (which allows the roof assembly to be unrated) the resulting ceiling temperature of 295 degrees C combined with an ambient temperature of 22 degrees C for a total temperature of 317 degrees C allows the use of the foamed plastic insulation in the roof assembly. The same principle of sprinkler protection, the Applicant 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 330 degrees C to 600 degrees C, but since this wood is treated it would not ignite until 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 there, specifically the plywood, would not ignite.

Another advantage of using plywood as a nailing surface instead of the permitted combustible cant strips is that it creates fewer voids in the roof assembly. Such wood strips, if used, also add significantly to the allowable combustible load in a roof assembly, the Applicant noted.

For these reasons, the Applicant argued that the proposed roof assembly provides sufficiency of compliance with Sentences 3.1.5.3.(1) and (2) of the OBC.

  1. Respondent's Position

The Respondent submitted that the proposed use of combustible plywood, albeit treated with a fire-retardant, in a roof assembly of a building required to be of noncombustible construction does not provide sufficiency of compliance with Sentences 3.1.5.3.(1) and (2) of the OBC. He noted that Sentence 3.1.5.3.(2) specifically allows an exemption to this and permits a combustible roof sheathing under certain conditions. However, he indicated that in the case at hand these conditions were not being met.

The Respondent also noted that the wall assembly tests regarding the propagation of flame in the air space are not relevant because these tests were done on walls at 90 degrees to the horizontal, not at 30 degrees as is the proposed roof.

Lastly, the Respondent pointed out that the plywood is above the roof sprinkler system and is therefore unprotected from above.

  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-grits with a 25 mm air space and R19 fibreglass batt insulation mounted on a 38 mm metal decking provides sufficiency of compliance with Sentence 3.1.5.3.(1) and (2) of the Ontario Building Code at the Loblaws Supermarket, 1048 Midland Avenue, Kingston, Ontario.

  1. Reasons

(i) Class A shingles will be used.

(ii) For Trent treated plywood, when the flame source is removed, the treated wood ceases to char and since it will not support combustion the flame will not spread.

(iii) The treated timber is considered equal or better than the permitted combustible nailing strips and foam insulation.

Dated at Toronto this 26th day in the month of August in the year 1999 for application number 1999-64

Mr. Kenneth Peaker, Chair-Designate

Mr. Fred Barkhouse

Mr. John Guthrie