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BCC Ruling No. 00-03-735

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

AND IN THE MATTER OF Sentence 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. Simon Ng, Architect, Simon Ng Architects, Toronto, Ontario, for the resolution of a dispute with Mr. John Wright, Chief Building Official, Town of Markham, Ontario, to determine whether the proposed roof, designed to delay the run off of rainwater but which is engineered to support either snow or rain load but not both, complies with Sentence of the Ontario Building Code at the Toronto Chinese Community Church at 100 Acadia Avenue, Markham, Ontario.


Mr. Simon Ng, Architect
Simon Ng Architects
Toronto, Ontario

Mr. John Wright
Chief Building Official
Town of Markham

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

Toronto, Ontario

February 3, 2000

February 3, 2000

Mr. Simon Ng, Architect
Simon Ng Architects Ltd.
Toronto, Ontario
The Applicant

Mr. Chris Bird
Manager of Plans Review
Town of Markham
Designate for the Respondent


  1. The Applicant

Mr. Simon Ng, Architect, Simon Ng Architects, Toronto, Ontario, has received a building permit under the Building Code Act, 1992, and is currently constructing a church building known as the Toronto Chinese Community Church, located at 100 Acadia Avenue, Markham, Ontario.

  1. Description of Constrution

The Applicant is currently constructing a new church structure classified as a Group A, Division 2 assembly occupancy. The building is described as three storeys in building height, 2,868 m2 in building area and of noncombustible construction. It will be equipped with a fire alarm system and a sprinkler system. The subject project is the last phase of a three building, 3.035 ha site that initially commenced development in 1987.

As part of his overall strategy to manage surface water on the site, the Applicant is also proposing to slow the discharge rate of rain from the roof of the proposed church by using six (Zurn Control-Flo) flow control hoppers. A total of 15 intake slots will be provided among the six roof control hoppers. Through their design and positioning on the roof, these devices would permit a maximum accumulation of water measured at 57 mm deep. At this depth the roof would hold a total of 158 m3 of water for delayed run off purposes. Drainage from the flow control hoppers will be provided by a connected piping system that will ultimately flow to a 200 mm pvc pipe to be located 1.2 m below grade and which will extend under the west side of the building to an over-sized storm sewer that the Applicant is proposing to construct on the west and south of the building that will provide at least 78.5 m3 of extra capacity.

The construction in dispute involves the design of the roof structure with respect to its support of live loads. In terms of structure, the roof has been designed only to support snow load plus the Subsection 2.5.1. 24 hour rain fall. The proposed roof is described as flat and has several different levels. A parapet of varying heights surrounds the roof. The framing construction of the building is structural steel.

  1. Dispute

The issue at dispute between the Applicant and Respondent is whether the proposed roof, designed to delay the run off of rainwater but which is engineered to support either snow or rain load but not both, complies with Sentence of the Ontario Building Code. This provision stipulates that a roof, with certain exceptions such as where it is "intended to provide rain water retention", need not be designed based on the consideration that rain loads will "act simultaneously with" snow loads. Put simply, unless a roof is intended to store water, it does not need to be capable of structurally supporting snow as well as rain load.

Rain water retention provided on the roof of a building is done as a method of storing and managing stormwater on some properties. In such cases, rain water is held on the roof for a certain period and is released over time through devices such as flow control roof drains. It is these stormwater storage roofs to which Sentence is meant to apply. In the dispute at hand, the Applicant has indicated that the proposed roof is not a stormwater retention facility as intended in the OBC, but he has included flow control drains in his roof design and he does intend to slow the drain off of rain water from the roof so that it takes approximately 4 to 6 hours.

The OBC, however, offers no clarification regarding rain water retention, specifically how long water must be held before it is considered stored or retained and what the roof design implications are of storing water. To address this issue, the Housing Development and Buildings Branch of the Ministry of Municipal Affairs and Housing issued a formal Branch Opinion on April 28, 1999 stating that if certain conditions were met in the roof design, the structure would not need to be considered as providing retention of rain water and would not have to be engineered as such.

The issue at dispute then is whether, through an interpretation of Sentence, and by considering the intent of this provision as stated in the Branch Opinion and its attached conditions, the proposed roof, as designed, should be regarded as providing retention for rain water and thus must be designed for the combined live loads of snow and rain.

  1. Provision of the Building Code

Sentence - Specified Rain Load

(3) Except as provided for in Sentence and except where a roof is intended to provide rain water
retention, loads due to rain need not be considered to act simultaneously with loads due to snow.

  1. Applicant's Position

The Applicant submitted that the proposed roof complies with Sentence of the OBC. He based this assertion on the premise that their rain water control strategy proposed for the roof is only a 4 to 6 hour temporary delaying of run off and is not retention for the purposes of stormwater management, as the officials from Markham argue. He indicated that their stormwater management plan utilizes the existing unused capacity on the rest of the site as well as constructing an over-sized sewer as part of the current work for the exclusive use of the church. The plan does not rely upon any assumed storage of water on the church's roof. As a result, since the roof is not intended to store water, the building does not need to be constructed to support snow and rain live loads.

The Applicant argued that the Opinion released by the Housing Development and Buildings Branch on April 28th, 1999 supports his position. He indicated that the proposed church will fulfill the four conditions set out in the Branch Opinion. As he noted, the drain down time will be far less than 24 hours, scuppers will be installed and the roof water depth will not exceed 57 mm, the roof drains will be closer than 15 m to the edge of the roof and less than 30 m to each other, and there will be six drains serving a total roof area of 2,790 m2.

The Applicant also noted that he has made direct inquiries with the Canadian Institute of Steel Construction and the Housing Development and Building Branch regarding the intent of Sentence and its application with respect to the structural design of a building.

In conclusion, he stated that the current interpretation of the Markham Building Department regarding the use of roof control flow hoppers forces unnecessary and additional construction costs on project proponents in the form of enhanced structural support in the building or extra capacity in underground storage tanks.

  1. Respondent's Position

The Respondent submitted that he interprets Sentence of the Code as requiring that both snow and rain loads be considered when the proposed roof is intended to retain water. As he stated; "the stormwater management consultant for the subject project has designed a stormwater drainage system that intentionally relies upon the storage (actual wording used by the consultant) of 158 m3 of stormwater on the roof of the subject building. This quantity has been calculated using a 1 in 100 year storm event as required by the Town of Markham Engineering Department. It is the opinion of the chief building official therefore that the roof must be designed to support the simultaneous loading of rain and snow as required by Sentence"

The Respondent argued that "the branch opinion issued in April of 1998 addressed the general use of flow control roof drains and their effect on the design of roof structures." This opinion, he added, "which was based on provisions contained in the 1995 National Pluming Code, was intended to clarify that where flow control roof drains are routinely utilized outside the scope of a stormwater management design, loads due to rain need not be added to loads due to snow." The Respondent continued by noting that the opinion, however, concludes by stating that "where the roof drainage system exceeds the limitations (set out in the conditions) contained above or where the roof is designed for permanent storage of stormwater, the potential for additional structural loading of rain and snow has to be considered." He argued that this was the case in the present proposal since, in his view, the roof has been designed with the intention of storing water.

To support his interpretation, the Respondent then presented arguments about the development of this provision and in particular its recent amendment in the current version of the Building Code. He argued that the change was included to clarify that roofs that are to retain water must be built for snow and rain load. It did not provide any relaxation for roofs that are to temporarily hold water.

For the above reasons, the Respondent concluded by stating that the requirements of Sentence applies to this application and both loads should be considered in the design and construction of the church.

  1. Commission Ruling

It is the decision of the Building Code Commission that the proposed roof, designed to delay the run off of rainwater but which is engineered to support either snow or rain load but not both, complies with the requirements of Sentence of the Ontario Building Code for the Toronto Chinese Community Church at 100 Acadia Avenue, Markham, Ontario, provided:

a) The maximum drain down time does not exceed 24 hours;
b) Scuppers are installed so that the maximum depth of water on the roof cannot exceed 150 mm;
c) Drains are located not more than 15 m from the edge of the roof and not more than 30 m from adjacent drains; and,
d) There is at least one drain for each 900 m2 of roof.


1) The structural design of a roof incorporating flow control roof drains need not be treated any differently from a conventionally drained roof if the roof drainage system conforms to the conditions listed as a), b), c) and d); and,
2) The roof system is designed as part of a stormwater management system for delaying discharge of rainwater and is not designed as a storage facility.

Dated at Toronto this 3rd day in the month of February, in the year 2000, for application number 1999-78.


Mr. Kenneth Peaker, Chair-Designate


Mr. John Guthrie


Mr. Robert De Berardis