This Recovery Advisory, focused on one- and two-family dwellings, presents important fire safety recommendations for design professionals, including architects, engineers, installation professionals and contractors to reduce the likelihood of ignition and structure-to-structure fire spread in single family homes during a wildfire, where building setbacks and defensible space may be limited. While most of the recommendations are best implemented during the design phase of a new home or community, some could also be implemented during a residential retrofit or mitigation. The recommendations in this Recovery Advisory are best practices and may exceed the requirements set forth in the adopted building codes and those specific to the Wildland Urban Interface (WUI)1. This Recovery Advisory does not address other important aspects of wildfire mitigation such as mitigation or renovation of existing homes, defensible space provisions, parcel-to-parcel fire spread, siting and non-building envelope attributes.

Vulnerable building envelope components and systems that can contribute to structure ignition and fire spread can include the following:

The following sections describe recommended design components of new construction systems listed above.

Due to the complete destruction of more than 2,200 buildings in Lahaina and Kula during the 2023 fires, it is uncertain how roofing systems contributed to structure-to-structure fire spread. However, published research and studies of previous wildfires indicate that residential roofing systems are a key vulnerability to structure ignition because of their tendency to ignite due to radiant heat, embers and direct flame contact (impingement). When fires occur during high wind events, the roof covering can also become detached, exposing combustible elements of the roof substructure (e.g., underlayment, wood roof deck, weather resistant barriers, battens). To limit potential wind-driven fire vulnerability, roof systems should be able to resist the uplift forces associated with high winds per the Maui Building or Residential Code. From a fire safety perspective, the entire roof assembly should satisfy the requirements for Class A when tested in accordance with ASTM E108 or UL 790. That is, the full roof assembly tested as an assembly should meet the requirements of Class A, not just tests of the roof covering alone. Common roof coverings that achieve Class A ratings include most asphalt shingles, concrete-, brick-, or masonry-tiles, or metal panel/shingles.

When designing a roof for new residential structures, important fire-resistant considerations include:

Ash, embers, sparks and other burning material can lodge in unprotected roof penetrations, igniting a combustible roof deck or underlayment. Designers should specify the use of an approved penetration firestop system installed with a minimum positive pressure differential of 0.01 inch (2.49 Pascals) of water and tested in accordance with ASTM E 814 or UL 1479. Design considerations for specific roof systems or materials are described in the following table.

Many houses on Maui are spaced closely together, reducing the ability to meet defensible space recommendations. On all exterior walls, consider providing at least a 1-hour fire-resistant exterior assembly per ASTM E119. For areas that are within 15 feet of an adjacent structure (such as a shed or a neighbor’s home), combustible storage, or unmanaged vegetation, designers should consider if a 2-hour fire resistance rated exterior wall is feasible. Additionally, designers should choose products that meet or exceed the 10-minute direct flame exposure test in accordance with ASTM E2707. Designers should specify the use of noncombustible insulation inside of wall cavities and seal exterior wall openings with fire-resistant caulk.

While ASTM E119 considers heat penetration through the wall, it does not address fire spread on the surface. Avoid the use of combustible exterior cladding such as vinyl siding, which may melt, or wood siding, as there is uncertainty on the long-term performance of fire treated wood products on exteriors in hot humid climates. Additionally, care should be taken when specifying the use of a metal siding material, as it may warp when exposed to heat. Noncombustible exterior wall covering such as concrete (CMU blocks), cement board, masonry, three coat stucco or ignition resistant exterior is recommended. Note that the use of a noncombustible or ignition-resistant exterior wall covering does not supersede the need for fire resistance, where there is a potential for radiant heat and direct flame exposure. Consider limiting the number of aesthetic or architectural features that may trap embers or debris.

In neighborhoods with small lots and homes within close proximity, the home should be designed so that windows, doors and other openings are minimized or protected on sides adjacent to other structures.

Vents for plumbing, crawlspaces, dryers, soffits, attics and other openings without proper design or screening can allow for ember intrusion, which can cause a home to ignite. In residential design, reduce the number of vents if possible. Consider alternatives such as replacing under-eave vents with a soffited eave or an enclosed eave using noncombustible weather-resistant material.

Where vents are required, specify the use of ember and flame-resistant vents, if available. While not required by the Maui Building Code, the California Building Code Chapter 7A provides a list of vents that have been tested by the California State Fire Marshal (SFM) or meet the requirements of ASTM E2886, Standard Test Method for Evaluating the Ability of Exterior Vents to Resist the Entry of Embers and Direct Flame Impingement. It is important that the vent is corrosion resistant. Where these vents are not available, the designer should specify covering the vent with 1/8-inch stainless steel (choose stainless steel when available or corrosion resistant when stainless steel is not available) and noncombustible mesh. Dryer vents should include a metal flapper that remains closed when not in use. Exterior paint should not touch vent screening to avoid clogging the vent screen. All penetrations and space surrounding a vent should be finished with fire-resistant caulk.

Where flood openings (hydrostatic openings) are necessary, the design should be consistent with the National Flood Insurance Program (NFIP), Maui Residential Building Code, and Maui Floodplain Management Ordinances and all applicable code and ordinance appendices. Flood opening covers should be noncombustible and open automatically when exposed to floodwaters. Care should be taken to remove any debris accumulation in flood openings. Consider choosing engineered flood openings with a solid metal exterior flap to reduce the chance of debris accumulation, which could ignite upon contact with embers or flames.

Windows can break due to radiant heat, direct flame impingement or flying debris. Jalousie and single pane windows are at substantial risk of breakage during a fire event. Combustible doors or those with non-fire rated windows can also pose a risk for breakage and ignition.

The designer should review whether the home is sited in a windborne debris region which may require additional window protection. Windows and doors should meet the design requirements for the applicable windborne debris region.

Recommended strategies for windows and doors are described in the table below.

Residential design recommendations that reduce exposure also apply to detached and accessory structures, such as an ohana. Ensure that defensible space considerations are included when choosing accessory structure locations. Accessory structures, such as sheds, should be sited at least 30 feet from the home or other combustible structures, storage areas or combustible materials like fences. The design of the accessory structure should follow the recommendations in this Advisory. It is recommended that accessory structures be protected to the same level as the residence.

Sheds pose a risk to fire spread during a fire event. Consider replacing small plastic or wood storage sheds with a metal shed. Position the shed so that the door does not face the main structure on the parcel. Design defensible space surrounding the shed.

Carports are often used for storage of materials in addition to cars and are highly vulnerable to ignition. These structures are often placed adjacent to the lot line between homes, which increases the potential for fire spread. Carports must be open on at least two sides; otherwise, the design considerations for a garage should be met. When designing a carport, the roof should be provided with a Class A roof assembly and the floor should be noncombustible. The carport ceiling and walls should also be designed with noncombustible materials.

Elevated homes with open foundations are common for flood protection, for siting on a slope, or to maintain views. Elevated homes are at an increased risk of ignition and fire spread as the open space below the floor exposes more flammable surfaces. Recommended strategies for designing an elevated home for fire safety are described in the table below.

In addition to designing for wildfire, all seismic, flood and wind loads should be considered in any design.