Other considerations
It is also important to consider windows, doors, decks, and landscape design in the planning and design for fire-resistant building.
- Use fire rated windows and other glazing or feature multiple panes with at least one layer of tempered glass.
- Use fire rated doors.
- Construct decks using wood frames if necessary, but do so by using a fire-resistant finish material that extends to within 152.4 mm (6 in.) of the ground. Construct and finish cantilevers and other overhangs with noncombustible materials; and ensure that combustible materials are not stored beneath decks.
- Distance outdoor structures a safe distance from the house (this distance will vary regionally by code) so flames do not spread to the home, should they ignite.
- Consider landscape design as well. Homes should have a noncombustible 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. Gravel, brick, concrete, and stone are good options for noncombustible landscape features that can be used in this case.
- Space trees to avoid spreading fire from one another or to the home, and at least 3.05 m (10 ft) away from the home. These distances will vary by region, for example: within 3.05 to 9.14 m (10 to 30 ft) of the home, space trees 5.5 m (18 ft) apart. Between 9.14 and 18.3 m (30 and 60 ft) of the home, space trees 3.6 m (12 ft) apart, and between 18.3 and 30.5 m (60 and 100 ft) of the home, space trees 1.83 m (6 ft) apart.
- Include fuel breaks as landscape features. This includes noncombustible details such as concrete driveways, sidewalks, patios, and dry streams, each of which can help prevent the spread of flames.
| COULD THIS BE THE PERFECT HOUSE FOR RURAL CALIFORNIA? |
| To achieve its goal as a zero net energy (ZNE) building, reaching the highest levels of efficiency while also opting for sustainable materials, the Good Haus relied on stone wool insulation to super-insulate the structure’s walls, roof, and slab foundation. Rigid board insulation (100.2-mm [4-in.] thick) creates a continuous layer of insulation on the exterior of the home, while stone wool insulation batt fills the interior wall cavities to achieve a wall assembly with an overall R-value of R39. The thick layers of stone wool insulation help to keep temperatures inside the home stable, protecting it from moisture and providing critical passive fire protection, an important consideration, given the Good Haus’s location within California’s WUI zone. Stone wool on the roof (127 mm [5 in.]) provides fire safety and maximum efficiency, achieving a cozy R80 for the roof system, while stone wool rigid boards also prevent heat loss below the home’s slab foundation, insulating the slab to R21. The slab insulation features stone wool batts between sleepers, plus a layer of R30. The floor system features a layer of R23 batts between the I-joists that bring the floor system to R68. In addition to its contribution to high energy efficiency and resistance to fire, the project team chose stone wool insulation for its ability to help create a vapor open assembly with high drying potential, to avoid moisture issues due to wind-driven rain and to prevent mold and mildew in northern California’s hot and humid climate. The sound absorbency of the stone wool products was also key to occupant comfort, given the home is near a state highway and sound blocking was an important consideration. For further acoustical comfort, stone wool batts were used in interior walls to help create a peaceful and relaxing spaces. Atmosphere Design Build principals Mela Breen and David Good (the home’s designer and builder) also favored stone wool as a sustainable insulation choice. The natural raw materials and high recycled content of stone wool products were an ideal fit with Breen and Good as to sustainability and responsible building practices. The complexity of the design, with its cantilevers and steel deck foundation, required heightened attention to the air sealing and insulation details. In addition to the highly insulated envelope with stone wool insulation, the details for connections between interior and exterior structural members were extensive to provide specific graphics to avoid thermal bridges. The house uses triple pane windows and doors to maximize light, comfort, and performance. A CO2 heat pump water heater provides efficient domestic hot water delivery. Balanced heat recovery ventilation offers high indoor air quality (IAQ) and uniform temperature distribution. Super-efficient ductless mini splits provide indoor climate control. A 6.5 kW roof mounted photovoltaic (PV) system offsets the home’s energy usage—creating a ZNE building. With the stone wool insulation, meticulous air-sealing, the combination of products, critical design work, and attention to detail, the Good Haus achieved an airtightness of 0.6 ACH50, making it one of the tightest homes in California. |
Fire-resistant materials
When it comes to the building envelope, stone wool insulation is an ideal material in these fire-safe assemblies. Breen and Good recognized those benefits when selecting stone wool insulation for their build as it limits the spread of fire, minimizes heat transfer from the outside to the inside of the building, does not contribute to smoke development, and supports added design flexibility allowable in ASTM E2707 or NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Component, assemblies, including unlimited insulation thickness to meet increasingly stringent thermal requirements. Foam plastics, in contrast, are limited to maximum thicknesses.
The selection of stone wool insulation was a win-win solution for the challenges of building a high-performance home in a WUI zone. The project team achieved their aggressive goals for energy efficiency as well as fire resilience, and reaped additional benefits from the stone wool, including:
- Moisture resistivity—stone wool does not readily absorb moisture when exposed to water, while allowing vapor to pass through the assembly for superior drying capabilities.
- Dimensional stability—stone wool products avoid (prevent) gaps to maintain reliable thermal and mechanical property performance over time.
- Chemical inertness—stone wool insulation products are chemically inert and non-corrosive with no off-gassing, and are resistant to rot, mold, and fungi.
- Termite resistance—stone wool tests have demonstrated superior performance in areas with a high probability of termites.
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