Building area, grade and height in storeys

The method

1. Find grade. Grade is the average level of the proposed or finished ground next to the building at all exterior walls (OBC Div. A 1.4.1.2. "grade"OBC Div. A 1.4.1.2.(1) GradeGrade means the average level of proposed or finished ground adjoining a building at all exterior walls.). Add up the ground elevations taken around the walls and divide by the number of readings. Never use one wall or one point alone. Readings should represent every wall fairly (equal spacing, or equal wall lengths).
2. Find the first storey. It is the storey with its floor closest to grade and its ceiling more than 1.8 m above grade (first storeyOBC Div. A 1.4.1.2.(1) First storeyFirst storey means the storey that has its floor closest to grade and its ceiling more than 1.8 m above grade.). Compute ceiling elevation minus grade. More than 1.8 m: this level is the first storey, even if its floor is below grade. 1.8 m or less: it is a basement (basementOBC Div. A 1.4.1.2.(1) BasementBasement means a storey or storeys of a building located below the first storey.) and does not count.
3. Count storeys. Building height in storeys is the number of storeys from the floor of the first storey up to the roof (building heightOBC Div. A 1.4.1.2.(1) Building height (in storeys)Building height (in storeys) means the number of storeys contained between the roof and the floor of the first storey.). Then remove what OBC Div. B 3.2.1.1.OBC Div. B 3.2.1.1. Exceptions in Determining Building Height(1) A rooftop enclosure provided for elevator machinery, a stairway or a service room used for no purpose other than for service to the building, shall not be considered as a storey in calculating the building height. (2) Space under tiers of seats in a building of the arena type shall not be considered as adding to… lets you ignore:
   • a rooftop enclosure used only for elevator machinery, a stairway or a service room (Sentence (1));
   • the space above mezzanines whose total area is not more than 40% of the open area of the room and which stay open above, with no partitions over 1,070 mm (Sentence (3));
   • enclosed mezzanines that total not more than 10% of the floor area, and not more than 10% of the suite they are in (Sentence (4));
   • an enclosed space on a 40% mezzanine is allowed if it is not more than 10% of the room's open area (Sentence (7)). A second mezzanine level stacked over the first counts as a storey (Sentence (5)).
4. Find building area. Building area is the greatest horizontal area of the building above grade, measured to the outside surface of the exterior walls, or to the centre line of a firewall (building areaOBC Div. A 1.4.1.2.(1) Building areaBuilding area means the greatest horizontal area of a building above grade within the outside surface of exterior walls or within the outside surface of exterior walls and the centre line of firewalls.). Use the biggest floor plate, including cantilevers. Do not add storeys together.
5. Split at firewalls. Each portion on either side of a firewall is a separate building, except for a few listed purposes such as the fire alarm system (OBC Div. A 1.3.3.4.(1)OBC Div. A 1.3.3.4. Building Size Determination(1) Where a firewall divides a building, each portion of the building that is divided shall be considered as a separate building, except for the purposes of (a) a determination of gross area in Section 1.2. of Division C, (b) a fire alarm and detection system in Sentence 3.2.4.2.(1) of Division B or Article 9.10.18.1…).
6. Pick the Part. Part 9 applies to a building of 3 storeys or less with a building area not exceeding 600 m², used for Group C (not a retirement home), Group D, Group E, or Group F, Division 2 or 3 (OBC Div. A 1.3.3.3.OBC Div. A 1.3.3.3. Application of Part 9(1) Subject to Article 1.3.3.3B., Part 9 of Division B applies to all buildings described in Article 1.1.1.1. of 3 storeys or less in building height, having a building area not exceeding 600 m², and used for major occupancies classified as (a) reserved (b) Group C, residential occupancies other than buildings used…). Fail either number and the building goes to Part 3 (1.3.3.2.OBC Div. A 1.3.3.2. Application of Parts 3, 4, 5 and 6(1) Subject to Articles 1.3.3.1A., 1.3.3.3B., Parts 3, 4, 5, and 6 of Division B apply to all buildings described in Article 1.1.1.1. and (a) classified as post-disaster buildings, (b) used for major occupancies classified as (i) Group A, assembly occupancies, (ii) Group B, care, care and treatment or detention…).
7. Part 3: count streets. A building faces 2 streets when at least 50% of its perimeter is within 15 m of a street or streets, and 3 streets at 75% (OBC Div. B 3.2.2.10.OBC Div. B 3.2.2.10. Streets(1) Every building shall face a street located in conformance with the requirements of Articles 3.2.5.4 and 3.2.5.5 for access routes. (2) For the purposes of Subsections 3.2.2. and 3.2.5. an access route conforming to Subsection 3.2.5. is permitted to be considered as a street. (3) A building conforming to Article…). Add the lengths of wall within 15 m, divide by the full perimeter.
8. Part 3: read the table. Pick the article for the group, storeys and sprinkler status (for example 3.2.2.54.OBC Div. B 3.2.2.54. Group C, up to 3 Storeys(1) A building classified as Group C, other than a retirement home, is permitted to conform to Sentence (2) provided (a) it is not more than 3 storeys in building height, and (b) it has a building area not more than the value in Table 3.2.2.54. (2) The building referred to in Sentence (1) is permitted to be of… for Group C up to 3 storeys). In its table, go to the row for the number of storeys, then the column for the number of streets faced. The value is the maximum building area, which is a limit per floor plate, not for the whole building.