One way to do this is with a product like exterior stone wool continuous exterior insulation in the building envelope. This approach not only increases fire resistance but mitigates thermal bridging for a more efficient wall assembly, thereby meeting increasing energy efficiency standards. In this example, this wood-framed assembly has been rated with a one-hour fire resistance rating due to its incorporation of stone wool products. Here, the rigid insulation boards are fastened with structural screws on top of the water-resistive barrier, insulating and providing enhanced fire resistance to the exterior of the wall, while stone wool batts are friction-fit in the interior cavities of the framing. While dynamics are different between fibre cement and vinyl siding as vinyl does not provide any protection, the lesson is the same—it is what is behind the cladding that will make or break the assembly.
Other considerations
It is also important to include windows, doors, decks, and landscape design in the plan for fire-resistant building.
• Windows and all other glazing should be fire rated or feature multiple panes with at least one layer of tempered glass.
• Doors should be fire rated.
• Decks can use wood frames, but they should be finished with a fire-resistant material that extends to within 152 mm (6 in.) of the ground. Cantilevers and other overhangs should be constructed and finished with non-combustible materials. It is also good practice to ensure combustible materials are not stored underneath decks.
• Outbuildings, fences, and other outdoor structures are often permitted to be built with any material but is it a good idea to build using non-combustible materials wherever possible. They should also be kept a safe distance away from the house (that distance will vary regionally by code) so flames do not spread to the home should they ignite.
• Landscape design is important, too. Homes should have a non-combustible area within 1.5 m (5 ft) of the home’s perimeter. This means no structures, combustible vegetation, or wood mulch against the home that could ignite and spread flames to the home itself. Materials such as gravel, brick, concrete, and stone are good options for non-combustible landscape features that can be used around the home’s perimeter.
• Trees should be spaced to avoid spreading fire to each other or to the home, and at least 3 m (10 ft) away from the home. These distances will vary by region, but for example: within 3 to 9 m (30 ft) of the home, trees should be spaced 5.5 m (18 ft) apart. Between 9 and 18 m (60 ft) of the home, trees can be spaced 3.6 m (12 ft) apart, and between 18 m and 30.5 m (100 ft) of the home, trees can be spaced 2 m (6 ft) apart.
• Fuel breaks can and should be included as landscape features. This includes non-combustible details like concrete driveways, sidewalks, patios, and dry streams, each of which can help prevent the spread of flames.
Fire-resistant materials
Now it is time to discuss the fire-resilient materials in a little more detail. When it comes to the building envelope, stone wool insulation is an ideal material in these fire-safe assemblies; it limits the spread of fire, does not transfer heat from the outside to the inside of the building, and will not contribute to smoke development with added design flexibility for ASTM E2707 assemblies, including unlimited insulation thickness to meet increasingly stringent thermal requirements. Additional features and benefits of stone wool insulation include:
• Moisture resistivity when exposed to water, while allowing vapour to pass through the assembly for superior drying capabilities.
• Dimensional stability avoids (prevents) gaps to maintain reliable thermal and mechanical property performance over time.
• Chemically inert and non-corrosive with no off-gassing, and is resistant to rot, mould, and fungi.
• Superior performance in areas with a high probability of termites.
