3.1.5.11. Combustible Insulation and its Protection (1) Combustible insulation, other than foamed plastics, is permitted in a building required to be of noncombustible construction provided that it has a flame-spread rating not more than 25 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, where the insulation is not protected as described in Sentences (3) and (4). (2) Foamed plastic insulation having a flame-spread rating not more than 25 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, is permitted in a building required to be of noncombustible construction provided the insulation is protected from adjacent space in the building, other than adjacent concealed spaces within wall assemblies, by a thermal barrier consisting of (a) not less than 12.7 mm thick gypsum board mechanically fastened to a supporting assembly independent of the insulation, (b) lath and plaster, mechanically fastened to a supporting assembly independent of the insulation, (c) masonry, (d) concrete, or (e) any thermal barrier that meets the requirements of classification B when tested in conformance with CAN4-S124-M, “Standard Method of Test for the Evaluation of Protective Coverings for Foamed Plastic”. (3) Combustible insulation having a flame-spread rating more than 25 but not more than 500 on an exposed surface, or any surface that would be exposed by cutting through the material in any direction, is permitted in the exterior walls of a building required to be of noncombustible construction, provided the insulation is protected from adjacent space in the building, other than adjacent concealed spaces within wall assemblies, by a thermal barrier as described in Sentence (2), except that in a building that is not sprinklered and is more than 18 m high, measured between grade and the floor level of the top storey, or in a building that is not sprinklered and is regulated by the provisions of Subsection 3.2.6., the insulation shall be protected by a thermal barrier consisting of (a) gypsum board not less than 12.7 mm thick, mechanically fastened to a supporting assembly independent of the insulation and with all joints either backed or taped and filled, (b) lath and plaster, mechanically fastened to a supporting assembly independent of the insulation, (c) masonry or concrete not less than 25 mm thick, or (d) any thermal barrier that, when tested in conformance with CAN/ULC-S101-M, “Standard Methods of Fire Endurance Tests of Building Construction and Materials”, will not develop an average temperature rise more than 140°C or a maximum temperature rise more than 180°C at any point on its unexposed face within 10 min. (4) Combustible insulation having a flame-spread rating more than 25 but not more than 500 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, is permitted in the interior walls, within ceilings and within roof assemblies of a building required to be of noncombustible construction, provided the insulation is protected from adjacent space in the building, other than adjacent concealed spaces within wall assemblies, by a thermal barrier as described in Sentence (2), except that in a building that is not sprinklered and is more than 18 m high, measured between grade and the floor level of the top storey, or in a building that is not sprinklered and is regulated by the provisions of Subsection 3.2.6., the insulation shall be protected by a thermal barrier consisting of (a) Type X gypsum board not less than 15.9 mm thick, mechanically fastened to a supporting assembly independent of the insulation and with all joints either backed or taped and filled, conforming to (i) CAN/CSA-A82.27-M, “Gypsum Board”, (ii) ASTM C 36, “Gypsum Wallboard”, (iii) ASTM C 442, “Gypsum Backing Board and Coreboard”, (iv) ASTM C 588, “Gypsum Base for Veneer Plaster”, (v) ASTM C 630, “Water Resistant Gypsum Board Backing”, (vi) ASTM C 931, “Exterior Gypsum Soffit Board”, or (vii) ASTM C 960, “Predecorated Gypsum Board”, (b) non-loadbearing masonry or concrete not less than 50 mm thick, (c) loadbearing masonry or concrete not less than 75 mm thick, or (d) any thermal barrier that, when tested in conformance with CAN/ULC-S101-M, “Standard Methods of Fire Endurance Tests of Building Construction and Materials”, (i) will not develop an average temperature rise more than 140°C or a maximum temperature rise more than 180°C at any point on its unexposed face within 20 min, and (ii) will remain in place for not less than 40 min. (5) Combustible insulation, including foamed plastics, installed above roof decks, outside of foundation walls below ground level and beneath concrete slabs-on-ground is permitted to be used in a building required to be of noncombustible construction. (6) Thermosetting foamed plastic insulation having a flame-spread rating not more than 500 which forms part of a factory-assembled exterior wall panel that does not incorporate an air space is permitted to be used in a building required to be of noncombustible construction provided (a) the foamed plastic is protected on both sides by sheet steel not less than 0.38 mm thick which will remain in place for not less than 10 min when the wall panel is tested in conformance with CAN/ULC-S101-M, “Standard Methods of Fire Endurance Tests of Building Construction and Materials”, (b) the flame-spread rating of the wall panel, determined by subjecting a sample including an assembled joint to the appropriate test described in Subsection 3.1.12., is not more than the flame-spread rating permitted for the room or space which it bounds, (c) the building does not contain a Group B or Group C major occupancy, and (d) the building is not more than 18 m high, measured between grade and the floor level of the top storey. (7) Foamed plastic insulation having a flame-spread rating of not more than 500 which forms part of a factory-assembled interior or exterior wall or ceiling panel that does not incorporate an air space is permitted to be used in a building required to be of noncombustible construction provided (a) the building is sprinklered, (b) the building is not more than 18 m high, measured between grade and the floor level of the uppermost storey, (c) the building does not contain a Group A, B or C major occupancy, (d) the panels are listed for compliance with ULC/ORD C376-1995, “Fire Growth of Foamed Plastic Insulated Building Panels in a Full-Scale Room Configuration”, and (e) the flame-spread rating of the wall panel, determined by subjecting a sample, including an assembled joint, to the appropriate test described in Subsection 3.1.12., is not more than the flame-spread rating permitted for the room or space which it bounds.