Significant savings through insurance premiums thanks to inherent fire resistance
Fire Resistance and Insurance
Fire separations are required by the building code to isolate units, or parts of a building, from each other in the event of a fire. The floors and walls separating the units must therefore have a certain fire resistance, as determined in accordance with the Building Code. In the event of fires, these walls, along with the floors, must form a fire-resistant compartment that prevents the fire from spreading to the rest of the building. In loadbearing masonry buildings, many of the loadbearing walls (usually including demising walls between units in residential buildings) also serve as fire separations. Hollowcore concrete slabs, which are often used as the floor system, typically serve as the horizontal fire separation between storeys.
A typical wood building that meets the minimum requirements of the National Building Code of Canada (NBCC) will have fire-resistant walls and floors made of a complex system of lumber, plasterboard (often two layers on each side of a wall are required) and mineral wool. However, if these are damaged during use (for example, drilled to hang a photo frame), their fire resistance may be affected. The accumulation of damage over the years could cause a significant discrepancy between the actual resistance and that intended by the designer. On the other hand, the hollowcore slabs that form the floors of loadbearing masonry buildings are non-combustible and offer twice the fire resistance required by the building code for typical mid-rise residential buildings. Similarly, 20 cm thick loadbearing masonry walls are also non-combustible and offer much more than the minimum fire resistance required by the code. Furthermore, plasterboard which could be added as a surface finish may further improve the performance of this system. When the loadbearing system of a residential building is constructed of masonry, masonry walls can be arranged to create effective fire separations between units. In this way, the units become fire compartments with durable partitions (walls and floors) that are not likely to lose their fire resistance during the life of the structure. Table 1 shows the composition and fire resistance rating (FRR) of typical floor systems for wood and masonry construction, and Table 2 shows the composition and fire resistance of walls.
Table 1: Composition and fire resistance of floors
Table 2: Composition and fire resistance of walls
*Required to reduce sound transmission
Tableau 1: Composition et résistance au feu de planchers
Tableau 2: Composition et résistance au feu de murs
*Requis pour réduire la transmission du son
The use of non-combustible masonry construction also reduces the risk of insurable damages (including the risk of fire) compared to other modes of construction. This is reflected by the commensurately lower cost of builder’s risk insurance during construction. For example, insurance costs for a four-storey masonry building in Toronto were found to be less than half that for the same building if constructed from conventional wood framing. Well beyond costs, the lack of combustible materials on a jobsite promotes worker safety during construction. Once the structure is completed, the strong resistance to fire spread in a masonry structure, constructed with durable fire separations between each unit, improves comfort and safety for the tenants, and reduces insurance costs for the owner. The tenants can be confident that they, themselves, as well as their belongings will remain safe: in the event of a fire in a neighboring unit, the risk of the damage spreading to other parts of the building remains very low.
Until here, masonry construction is compared to wood construction. Many of the advantages of masonry construction will be the same for cast-in-place concrete construction (for example, the advantages of non-combustible construction and the degree of fire resistance of floors); however, the walls that separate housing units in a cast-in-place concrete building often have a similar composition to the walls of a wood building (steel or wood studs, plasterboard, insulation) and therefore share their degree of fire resistance. Due to structural requirements, the walls of loadbearing masonry construction already ensure excellent performance in terms of fire resistance (almost twice the minimum required). This ensures the comfort and safety of occupants throughout the life of the building. Since this type of construction can be done at a similar cost, and sometimes even a lower cost, compared to that of conventional wood-frame construction, and at a much lower cost than cast-in-place concrete construction, loadbearing masonry construction is an obvious choice for many projects.
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