6.1.7 Building Firewalls and Disciplinary Bridges

“Actions intended to reduce short-term risk (e.g. fire suppression) can produce positive feedbacks that lead to elevated longer-term risk of loss to high- severity fires. This and other maladaptive responses to fire-prone ecosystems have catalysed destabilising (positive) feedbacks” Spies et al, 2014.

The original ‘fire walls’ defended not against computer viruses. Providing 6> hours of fire resistance their various designs prevented against the spread of fire by limiting ignition by firebrands, and compartmentalising fire outbreaks (Fan, 2001). However, the walls were but the second line of fire defence, the first being the creation of a fire break, of which one variant was the building of roads, as was utilised in the planning of Zhou City two millennia ago (Ibid). Fast forward from the age in which Confucianism and Taoism became the predominant schools of Chinese philosophical thought, and one finds western science aligning to one and the same strategy.

Within the WUI fire-risk assessment extends beyond the building and into the landscape. As in the adjacent wildland, the probability of a fire outbreak varies greatly from one location to another, and one season to another, with the odds coupled across a matrix of factors including weather conditions, fuel state, and availability of ignition sources. Presently, as has been the case for some several decades, U.S. wildland policy favours vegetative thinning via methods including clearing, prescribed burning [125], grazing, and mechanical thinning far beyond the WUI boundary. As discussed earlier, the underlying premise is that in reducing the quantity of fuel, forest agencies reduce the probability of fires that grow to such scale and intensity as can be not ‘fought’, and that consequently spread to the WUI. However, an ever-growing body of studies now challenges this engineering-led approach, highlighting that, unlike gardens, no matter the scale of the budget as is assigned thereto [126], ‘wild’ lands are beholden not wholly to human actions. Syphard succinctly summed up the situation in stating that “despite enormous investments in wildland fuel manipulation, improvements in fire-safe codes, and building regulations, and advanced fire suppression tactics” structural loses to wildfire have increased (2012, online). Additionally, as posited by Pyne (2010), the policy may incline some homeowners within the WUI to wrongly assume it provides of protection against wildfire. Hence, several recent studies and publications have advocated for restricted development in the foremost fire-prone locations (Moritz et al, 2014; Mann et al, 2013; Gibbons et al, 2012; Pyne, 2010), and for a ‘radical rethink’ in the design and planning, at both the building and landscape scale, for the WUI as a whole (Pyne, 2017).

Conversely, the landscaping immediately adjacent to a structure impacts greatly on its odds of ignition (Moritz et al, 2014). Gibbons et al estimated that, in severe fire weather, “reducing trees and shrubs from 90% to 5% cover within 40m could potentially reduce house loss by an average of 43%” through limiting exposure to burning embers and radiant heat, while also creating defensible space (2012, p.2). Additionally, whereupon the upwind distance of structures to trees and shrubs is increased from 0 to 100m the probability of the former’s ignition is predicted to reduce by 26% (Ibid). Earlier studies support Gibbons et al’s findings, concluding that in “worst case scenario” structures standing a minimum of 30m from forests and shrublands constitutes a “safe distance” (Mell et al, 2010, p.242). However, the above probabilities are averages and in the many and diverse real-world scenarios ratios rise and fall depending on factors including but not limited to the local fire regimes, weather patterns, topography, fuel state, and duration and proximity of past fires. Thus, deciphering “the problem is complex and contingent, requiring continual attention to the changing circumstances of stakeholders, landscapes, and ecosystems” at multiple spatial and temporal scales (Gill et al, 2013, p.438).

In and around structures, homeowners are advised to remove dead vegetation and debris; plant fire-resistant shrubs; maintain an irrigated area and low vegetation; remove branches >3m of roofs; space shrubs 4.5m> apart; prune lower branches within >9m of structures; stack wood 9m> from residence; and, as above, limit tree density >30m (Todman et al, 2012). However, the privacy and views that are facilitated by foliage tend to deter some homeowners and businesses from taking such measures (Spies et al, 2014).

As during the Zhou Dynasty, roads play a fundamental part in efforts to prevent wildfires from consuming structures. Akin to firebreaks, roads also provide defensible space, evacuation routes, and enable fire trucks and crews to penetrate the wildland. Hence, whereupon the WUI expands in the absence of additional road links the probability of new buildings being consumed by wildfire tends increase (Ibid.). However, studies from wide-ranging regions evidence that the more roads expand into the wildland the greater the adverse impact to biodiversity [i.e. roadkill] (Gaskill, 2013; Hardy and Seilder, 2014) and the greater the probability of fire [i.e. ignition by sparks emitted from a vehicle] (CALFIRE, 2017). But, at The Tree Farm (Brook Resources, 2017) near Bend, Oregon, which opened in 2016, by means of optimising the speed at which fire crews can attend a blaze, homes have been clustered to “simplify the system of access roads” (Brey, 2017). While advantageous to the site’s residents, in containing development ‘residential clustering’ also reduces anthropogenic impact to the neighbouring forestland.

Yet another way in which fire mitigation methods of the modern-day West align to those of the ancient East is with respect to water accessibility. From the earliest regional endeavours in city planning, proximity of Zhou structures to water sources including ponds, lakes, canals, and rivers was a predominant factor in deciphering the positioning of palaces, temples, and civic offices. In addition to landscape water features, large copper and iron water vats were strategically placed around structures, giving ready access in the event of a fire (Fan, 2001). However, hydrological shifts make this not evident to all but the trained eye today, for most of the historical water sources have now run dry (Ibid), this being pertinent to the present and near-future of the western U.S., where though residents in fire-prone regions are recommended to install additional water supplies (Todman, 2012), persistent drought is rapidly changing regional hydrology (Cody et al, 2015). Compounding the significance thereof, recent studies suggest that fire retardants as had been thought innocuous pose a threat to the health of both flora (Hogue, 2011) and fauna, humans included (Knaus, 2017; Davidson, 2017).

>Continue to Chapter 6.1.8 here.

Footnotes

[125] Prescribed burning refers to fires that have been ignited with explicit intent to reduce fuel availability at a predefined site and landscape scale.

[126] In reference to the fact that, despite the U.S. Forest Service’s annual fire suppression budget having risen by 40% since the mid 1990s, during this past two decades the number of structurally destructive fires in the WUI have increased severalfold (USDA, 2018).

The thesis is also available in PDF format, downloadable in several parts on Academia and Researchgate.

Note that figures have been removed from the digital version hosted on this site, but are included in the PDFs available at the links above.

Citation: Sterry, M. L., (2018) Panarchistic Architecture: Building Wildland-Urban Interface Resilience to Wildfire through Design Thinking, Practice and Building Codes Modelled on Ecological Systems Theory. PhD Thesis, Advanced Virtual and Technological Architecture Research [AVATAR] group, University of Greenwich, London.