b'FIRE SAFETYThe assembly of the same configura-tion was then exposed to higher heating Figure 1:Effective thermal conductivity of green roof growing medium. loads.Figure3presentsthetempera-turesofthedeckobtainedfroma numerical model applying heating loads of different intensities: 50, 100, 150 and 200 kW/m. It shows that a deck failure can occur when applying a heating load greater than 150 kW/m and during a period of more than three hours. This analysis suggests that a 10-cm layer of growing media insulates the roof well by retarding the propagation of heat for at least three hours when exposed to severe Figure 2: Temperature profiles in the assembly. heat load. The German guideline FLL Figure 4: Time to failure dependency of substrate layer thickness when applying heating loads of 50 and 200 kW/m in assem-blies on the wooden deck, with or without protection by gypsum board.Figure 4: Time to failure dependency of substrate layer thickness when applying heating loads of 50 and 200 kW/m in assemblies on the wooden deck, with or without protection contains a description of a green roofprotection. Figure 4 presents how time that is considered resistant to radiant heatto failure changes with different thick-by gypsum board. when substrate layer thickness is at leastnesses of substrate. Red curves show the 3 cm. In Canada and the United States,results for the assembly with no gypsum most green roofs have a minimum of 10overthewooddeckwhenapplying cm, thus making it sufficient to resist theheatingloadsof50and200kW/m downward propagation of heat to thefor comparison. In both cases, time to roof deck. failure decreases greatly.Figure 3: Temperature evolution at the deck level when aSmallerthicknessesofasubstrateBased on the graph, it is clear that Figure 3: Temperature evolution at the deck level when a green roof is exposed to four green roof is exposed to four different heating loads. layer,however,maynotprovidesuchusingagypsumboardovertheroof different heating loads.deckcaneffectivelyreducethefire risksbyincreasingthetimetofailure of the structure. The blue curve shows that a delay of at least 30 minutes can be provided for failure time in extreme heat conditions for substrate thicknesses IS BECOMING between 3 and 10 cm.Fromtheanalysisoftheeffectof the substrates porosity on fire risks foraroofdeck,itwasconcludedthata better compacted growing media retards Figure 5: Comparison of HRRs of vegetation and typical roof coverings: (a) dead parts theheatpropagationbetter.However, thiseffectwasvisibleonlyforhigh (Madrigal et al. (2012)); (b) green leaves (Madrigal et al. (2012)); (c) PMB membrane with heating loads.fire retardants (Bourbigot et al. (2013)); (d) PMB membrane without fire retardants Finally,greenroofsinstalledover (Thureson and Nilsson (1994)).decks showed better performance steel in fire, since the structure never reached its critical temperature, even in extreme SAME PEOPLE, SAME SERVICE, heatconditionsandwiththegrowing NEW LOOK! medium of only 3 cm.PART 3: FLAMMABILITY CHARACTERIS-TICS OF GREEN ROOFS (2020) WHITECAPSUPPLY.COM The primary concern about green roofs andfirerisksisthecombustibilityof green roof components, such as plants @whitecapsupply and soil organic matter. They are claimed to present an additional fuel load that can 26 lROOFINGBClSPRING 2024'