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Designing for Resiliency: Part III

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A Coupled Approach

In recent posts, we’ve explored how site management and defensible space strategies can be utilized to enhance the fire resiliency around a structure. In the final post of the series, we’ll examine how the structure itself plays a role in fire resilient design and how hardening techniques can be used in conjunction with defensible space strategies to provide a coupled approach to fire protection.

We’ll also explore some of the cost implications of fire resilient design and how engaging with the right partners can help in determining what strategies might be best suited for a particular project.

No structure can be completely fireproof, but various design strategies can be used to make a structure increasingly more fire resilient.

The Last Barrier – Structural Hardening

No structure can be completely fireproof, but various design strategies can be used to make a structure increasingly more fire resilient. In considering the structure itself, it’s important to think critically about the various vulnerabilities that exist, from the building envelope (openings and penetrations) to the materiality of the shell (roofing and siding), to the type of systems we put inside (fire suppression, fire alarm and mechanical systems) and how each play a role in whole structure protection.  We’ll look at each of these individually and also as part of a larger collective of resilient design decisions that work together.

Building Envelope

  • The building envelope is often composed of various openings and penetrations, that if not thoughtfully considered, can provide a direct path of travel for flames and embers into the structure.  In many cases, the interior of a structure is composed of highly flammable materials like furnishings, drapery, wall and floor covering, so keeping resilient barriers in place to prevent direct flame or ember contact is critical. The following opening protectives are examples of hardening strategies by component.  Note the California Building Code in some cases will have code mandated minimum requirements for some of the elements listed below, especially in fire prone WUI areas.
  • Windows and Glazing
    • Windows and glazed areas are one of the most vulnerable components of a structure, as they can provide a direct opening into the structure should the glazing break or lose structural integrity due to direct contact or radiant heat.  Consider the following mitigation strategies:
      • Multi-pane windows with a tempered outer pane
      • Low-E coating on windows
      • Non-combustible window frames (thermally broken aluminum being one of the better performers)
      • Install metal window screens to reduce embers direct contact
      • Fire-rated assemblies, which includes a tested assembly comprised of the frame and the glazing. Typical ratings range from 20 minutes to 2 hours. These ratings will come stamped on the window from the manufacturer.
      • Limit the amount of windows and the size on areas of the façade that face dense vegetation
      • Consider external metal fire shutters, to be deployed in a fire related event.
      • If using skylights, use glass panes in lieu of plastic.
  • Doors
    • Like windows, doors can provide a direct opening into the structure if not constructed with the proper assembly. Consider the following mitigation strategies:
      • Non-combustible and ignition resistant cladding (exterior finish)
      • Ideally a solid-core wood or metal door.
      • Fire-rated assemblies, typically with a minimum rating of 20-minutes.
      • Use seals and gaskets around the perimeter of the door itself, including the bottom of the door, to prevent both smoke and ember intrusion.
      • Garage doors shall limit any gaps around the perimeter to an 1/8” maximum and all jambs should be covered with metal flashing. Equip the door itself with a battery backup.
  • Sealing and Air Tightness
    • Creating an airtight building envelope can reduce the risk of smoke and embers intrusion by eliminating small gaps that are common-place in conventional construction practices. Consider the following mitigation strategies:
      • Install a fire rated WRB (Air and Water-Resistant Barrier) around the perimeter shell as opposed to a combustible barrier.
      • Seal all penetrations (outlets, vents, utility lines) with fire rated sealant/caulk.
  • Guards and Screens
    • Various openings or assemblies around the structure can and should deploy screens and guards to limit the intrusion of embers. Consider the following mitigation strategies:
      • Metal gutters in lieu of PVC or plastic
      • Debris guards on all gutters
      • Ember resistant vents for conditions like attic vents, crawlspace vents, heating ventilation and air condition vents (through-wall vents and roof vents)
      • Shutters over large vents like gable end vents and crawlspace vents

Building Materiality

  • The composition and materiality of the structural shell, specifically the roof and exterior walls are particularly vulnerable given the amount of surface area exposed.  As such, special consideration needs to be given to ensure these assemblies are thoughtfully designed to enhance resiliency as it relates to fire performance. Note the California Building Code will have code mandated minimum requirements for some of the elements listed below, especially in fire prone WUI areas.
  • Roofing
    • Roof coverings are typically fire rated ranging from Class A (more resistant) to Class C (less resistant), to unrated. Both the material and the assembly itself can carry a rating, depending on the situation. Meaning, you can have a Class A rated assembly, or you can utilize a Class A rated covering, which carries the rating as a standalone element. Consider the following mitigation strategies with regards to roofing:
      • Stand-alone Class A roof
        • Asphalt fiberglass composite shingles
        • Tiles – concrete, metal, clay or slate
        • Some metal roofing (by manufacturer)
      • Class A rated assemblies
        • Aluminum metal roofs
        • Some recycled rubber and/or plastic composite materials
      • Block annular spaces between the roof decking and the covering
      • Install non-combustible metal drip edge
  • Roof Overhang
    • The area under the roof (open eave or soffit) is very vulnerable to all forms of fire contact, including direct flame, embers and radiant heat. Consider the following mitigation strategies with regards to roofing overhangs:
      • Avoid open eaves, elect for soffited eaves or no overhang
      • If using a soffit, consider a 1-hour rated flat assembly
      • Consider unvented soffits
      • Limit re-entrant corners and roof valleys
  • Wall Assemblies and Materiality
    • Much like roof eaves, the exterior wall is susceptible to all forms of fire contact. Both the wall assembly itself and the materiality should be considered as key design elements. Consider the following mitigation strategies:
      • Non-combustible siding like concrete, fiber cement, three coat stucco, masonry and metal (steel)
      • Apply fire retardant coatings to combustible surfaces (if permitted by code) to elements like trim.
      • 1-hour rated wall assembly with
        • rated exterior sheathing
        • metal studs in lieu of wood
        • mineral wool in-wall insulation
        • Type X interior gypsum wall board on interior

Specialty Systems

  • The use of specialty systems are becoming increasingly more common in response to wildfire events.  These systems require planning ahead to ensure the right infrastructure is in place. Consider the following mitigation strategies:
    • Interior Fire Suppression Systems
      • Often tied to the municipal infrastructure system but can be well-based if pre-planned.
      • Can be triggered by connected fire alarm system, or
      • Types of systems include: wet (water based), dry (filled with compressed air until activated), deluge (multiple heads triggered simultaneously), pre-action (activated by smoke or heat, heads can act independently), foam (uses foam and chemical retardants)
    • Fire Alarm Systems
      • Smoke detectors in key areas. There should be one smoke detector in every bedroom, one in every hallway, and minimum of one on every level.
      • Heat detectors in key areas. Heat Detectors should be located in the kitchen, laundry room, and garage.
      • Can be monitored to connect/alert the owner and 911, along with shutting down systems like HVAC to limit smoke and ember intrusion and unlocking doors
      • Can be activated by both smoke and/or heat

A Cost-Conscious Decision for the Return On Investment

As the cost of building continues to increase throughout the industry, we recognize that the cost of construction is a key component in evaluating the feasibility of a project and that each decision needs to be weighed for the value added.  As designers, it’s our responsibility to help clients understand and evaluate both the initial upfront cost, the long-term maintenance costs and to help frame some of the intangibles, like peace of mind in an emergency. Although structures cannot be designed as fireproof, various design decisions can increase the amount of time a family has to safely evacuate, in addition to providing a higher probability that they will have something to come back to post fire.  Many of these strategies also have the ability to increase the resale value, by adding additional levels of protection in and around the home and lower long-term maintenance costs.  Although some of these strategies will add cost to the job, most of these decisions lead to negligible cost increases.

A 2018 study done by Headwater Economics¹, in conjunction with the Insurance Institute For Business & Home Safety, found that “a new home built to wildfire-resistant codes can be constructed for roughly the same cost as a typical home” and that “many wildfire-resistant home features have additional benefits, such as a longer lifecycle and reduced maintenance.” Although certain components have a higher rate of increased upfront cost, with roofing and landscaping being two of the biggest, over the life cycle of the building these design decisions often pay off.

Although some of these strategies will add cost to the job, most of these decisions lead to negligible cost increases.

THE TEAM APPROACH

Putting together the right team that understands not only the code and site constraints, but also one that respects the clients’ past experiences and what they hope to achieve in the current project is one of the most important decisions on a project.  HHA’s project delivery process ensures that thoughtful conversations are had at each stage of the design and that the right partners are part of the discussion to ensure the owner has the information needed to make an informed decision that best suits their needs.

To learn more about how we can work together to incorporate these design strategies in your project, please reach out to us at info@h-h-architects.com.

We’re here to help you navigate the re-build process. For a clear roadmap that outlines the essential steps ahead please download our Project Flow Chart here.

Citations:

¹https://headwaterseconomics.org/wp-content/uploads/building-costs-codes-report.pdf

Designing for Resiliency: Part II

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As a continuation of the series, we will next explore the ways in which site development can play a role in designing for resiliency.  The recent wildfires in LA have been a stark reminder that we must consider both the structure itself and the surrounding site when proposing design solutions that offer not only an aesthetic vision, but also ones that are thoughtful and responsive to the vulnerabilities of the surrounding area.  As stewards of the built environment, the design community has a responsibility to put forward solutions that consider the design of the surrounding site just as important as the building itself.  It is here where many of the resiliency strategies can help limit the spread of wildfires and mitigate the overall impact.

As stewards of the built environment, the design community has a responsibility to put forward solutions that consider the design of the surrounding site just as important as the building itself.

How Fire Moves

Understanding how wildfires travel is a key component to designing a structure and surrounding landscape that can withstand the effects.  There are three main ways fire moves, each of which requires their own set of design solutions.

  • Direct Flame
    • The direct contact that a flame makes can and will ignite materials that are of a combustible nature. Keeping flames low, providing fire breaks and building with non-combustible materials can limit the impact of direct flame contact.
  • Radiant Heat
    • The radiant heat generated by a wildfire can ignite materials from a distance as far away as 30 feet.  Larger fuels often burn hotter, therefore posing a great risk to the structure.  Limiting large fuel sources to distances beyond 30 feet from any structure and utilizing non-combustible materials and protected openings like multi-pane tempered windows can help limit the risk of radiant ignition.
  • Wind Driven Embers
    • 90% of homes ignite by direct contact with embers. Embers can travel anywhere from hundreds of feet and up to miles in distance with the right wind conditions.  These embers are often the first component of a fire to reach a site and not only ignite fuel sources around the home like vegetation, fencing and decks, but they can also pose a risk to the structure itself.  Utilizing hardscape materials, fire resistant landscaping and non-combustible decking and furniture can reduce a sites risk to ignition by embers. Home-hardening techniques like Class A roofing, using non-combustible materials for wall assemblies and sealing openings into the home are also effective strategies.

Site Characteristics

With an understanding of how fires travel in various ways to and through a site, the site itself must be examined to determine if any vulnerabilities exist that require design interventions to mitigate. There are a variety of decisions that go into the development of a site, but the first step is understanding the inherent characteristics that designers must ultimately respond to.

  • Topography – The natural contours of a site can dramatically impact the way in which a fire can spread, with steep inclines in grade accelerating a fires pace. Dense vegetation and debris runoff are prevalent on steep slopes, providing additional fuel for fires. The decision to work with or modify the existing contours is an important decision in site development, as is the location and orientation of the structure in response to this.
  • Wind Patterns – Much like topography, wind direction plays a significant role in the path a fire takes through a site. Understanding the direction the prevailing wind is coming from and how it is modified by both the terrain and surrounding structures will inform building orientation and location on a site. The design of additional site features like vegetation groupings, retaining walls (fire breaks) and locating prime fuel sources downwind of the structure can help reduce the impact of traveling embers.
  • Site Adjacencies – Every site is part of a larger collective, a community.  As important as it is to understand the key characteristics of the immediate site, it is equally as important to understand the surrounding area and landscape.  Examining the surrounding area to understand if steep terrain, overgrowth, dense vegetation, utility corridors or close adjacent structures exist can and should inform design decisions on a project site.

Defensible Zones

Once the main site characteristics are determined and the structure is located, the immediate surrounding area is then developed in a three-zone design strategy.  These zones (0-5 feet, 5-30 feet and 30 feet to 100 feet) are designed to become increasingly more resilient the closer to the structure you get.

  • Zone 0 (0 feet to 5 feet) Ember Resistant / Non-Combustible
    • Zone Intent: The goal in this zone is to create a non-combustible immediate barrier around the structure, which includes attached decks, to eliminate direct flame contact. The area closest to the structure should have fire-resistant materials, very minimal vegetation, and no combustible items like firewood.
    • Design Features:
      • Create separation between vegetation (if any).
      • Use hardscapes for features like driveways, seating areas and walkways that are of non-combustible materials like gravel, stone and concrete.
      • Select furniture that is made of non-combustible materials and separate from other potential fuel sources.
      • Decking:
        • If a deck is proposed, construct of non-combustible materials like composite boards, concrete or stone.
        • Limit any gaps between the deck boards and install a skirt made of non-combustible material to prevent embers from gathering.
        • Install foil-faced bitumen tape on the top surface the deck joists.
        • Limit growth under the deck by installing a stone bed over a weed barrier
      • Fencing, arbors and gates that are within 5 feet of the structure or attach directly to the structure should be made of non-combustible materials, like metal.
    • Routine Maintenance (post-occupancy)
      • Remove all dead plants or grass and dried leaves.
      • Do not store wood in this area.
      • Eliminate flammable plants and vegetation.
      • Do not store wood in this area.
      • Routinely clean gutters and roofs of branches, leaves and needles.
      • Do not install combustible systems like generators or propane tanks in this area.
      • Limit the storage or recycling in this area.
  • Zone 1 (5 feet to 30 feet) Intermediate Area – Lean, Clean and Green
    • Zone Intent: The goal in this zone is to reduce the risk of fire spreading to the structure from close fuel sources, via radiant heat and additional embers.
    • Design Features:
      • Limit vegetation to fire-resistant, native and water retaining plants, and locate in groupings with ample separation. Keep plant selection to low growing plants.
        • Burning vegetation can ignite adjacent materials through radiant heat and create additional embers as they burn.
      • Trees and shrubs should be limited to small clusters in discontinuous groupings.
      • Create fuel breaks with non-combustible pathways like gravel, stone and concrete.
      • Furniture groupings, play structures and fuel sources like grilles and propane tanks shall be separated.
    • Routine Maintenance (post-occupancy)
      • Mow grass to 4” max in height.
      • Clear vegetation from ignition sources (grilles, propane tanks, etc).
      • Clear debris and dead vegetation.
      • Limit the storing of any combustible materials like firewood.
      • Trim trees regularly.
  • Zone 2 (30 feet to 100 feet) Fuel Reduction Area
    • Zone Intent: The goal in this zone is to restrict the movement of fire and to limit its ability to progress towards the structure via traveling embers. This zone is primarily governed by vegetation and overgrowth management.
    • Design Features:
      • Vegetation Spacing:
        • Space between shrubs:
          • Flat or mild slope (less than 20%): Two times the height of the shrub.
          • Mild to moderate slope (20–40%): Four times the height of the shrub.
          • Moderate to steep slope (greater than 40%): Six times the height of the shrub.
        • Space between trees:
          • Flat or mild slope (less than 20%): 10 feet.
          • Mild to moderate slope (20–40%): 20 feet.
          • Moderate to steep slope (greater than 40%): 30 feet.
      • Locate secondary structures (ADUs, sheds) at least 30 feet from the primary structure.
      • Allow for extra vertical space between shrubs and trees.
      • Keep at least three times the height of any shrubs, between the shrubs and the lowest branch of trees.
    • Routine Maintenance (post-occupancy)
      • Clear areas around secondary structures and propane tanks.
      • Keep 10 feet of clearance to bare mineral soils and no flammable vegetation for an additional 10 feet around their exterior.
      • Keep 10 foot distance around wood piles, down to bare mineral soil, in all directions.
      • Remove all tree branches at least six feet from the ground.

Other Considerations

Beyond defensible space requirements, there are additional features and systems that can be installed to enhance the resiliency of a site and provide coverage continuity in the event of a weather-related event.

Water Features – Pools, spas and fountains can provide an owner with the ability to draw water from an on-site source quickly to proactively saturate the grounds ahead of a fire or reactively extinguish flames during an active blaze.  Planning ahead infrastructurally is key, as both a standalone power (generator) and pumping systems should be integrated into the design to properly utilize these features.

Landscaping Irrigation – The irrigation system used to support landscaping can also be activated in the event of a wildfire to saturate the surrounding area and limit the ability of embers and flames to ignite vegetation.  Note, to be used during the event of a fire, assume city wide utilities will not be in service and standalone water and power sources will need to be relied upon.

Underground infrastructure – Running utility infrastructure underground and where permitted, with flexible conduit can reduce the risk of line rupture and ignition.

Generator – Installing a generator can keep critical infrastructure running like power, along with life safety systems like fire alarm and fire suppression devices.

Monitoring System – Consider site and structure monitoring services for smoke, heat and ember related triggers.  Wildfire defense systems on the market utilize satellite data sources, cameras and heat sensors to track wildfires for an individual property 24 hours a day and can alert the owner to potential hazards. These monitoring services can also be tied to site irrigation or fire suppression systems for immediate activation.  More traditional heat and smoke detectors can be used in and around the structure to jointly notify both the owner and the monitoring agency.

Beyond Utility

The strategies discussed in this post have been explored at their foundational level with a focus on the utilitarian function to mitigate the effects of wildfires.  As design professionals, our role is to consider how to deploy each of these strategies in a manner that takes full advantage of their utilitarian function, while also creating compelling spaces that feel true to the fabric of the neighborhood and reflect the overall design strategy of the project. 

As part of our design process and through various methods like mood boards, 3-D visualization, iterative floor plans and elevations, along with collaboration sessions with the owner and larger consultant team, we are continuously pushing to thoughtfully compose each of the various elements into the design narrative in a cohesive manner. 

As design professionals, our role is to consider how to deploy each of these strategies in a manner that takes full advantage of their utilitarian function, while also creating compelling spaces that feel true to the fabric of the neighborhood and reflect the overall design strategy of the project.

What’s Next?

In the next post, we’ll explore home hardening strategies like materiality, envelope composition, building systems and fire protection systems to better understand their role in resiliency and the impact they can potentially have in a wildfire event.

To learn more about how we can work together to incorporate these design strategies in your project, please reach out to us at info@h-h-architects.com.

We’re here to help you navigate the re-build process. For a clear roadmap that outlines the essential steps ahead please download our Project Flow Chart here.