I am considering building an off-grid cabin in a remote area in Northern California which is in a high risk area for severe wildfires. The priority for the structure would be first-and-foremost survivability in the event of direct hit with a major wildfire or fire-tornado (survivability of the structure and potentially an occupant). As such all decisions on structural and cladding materials would be made to support this priority.
I read the story at:
(although the original reference link seems broken)
The discussion in that story largely centers on selection of fire resistant exterior cladding and roofing materials, but with the assumption of a wood framed structure, and the OP in that thread stated he did not want a ‘concrete bunker’.
I have somewhat different preference… I am fine with a ‘concrete bunker’ and am looking for building systems that can provide for a fully non-combustible building structure/envelope including the roof structure. Concrete, Rebar, Rockwool seem like good materials for this. Though, like the OP in that story, moving to Vermont is not a practical option for me.
My thinking is to use something like cast-in-place Thermomass with rockwool core for the walls, and pre-cast panels of similar composition for the roof. This would provide for building structure with a fully non-combustible composition. I would plan on adding rolling metal shutters to the windows and potentially an underground non-windowed cellar for shelter just in case I were unexpectedly trapped by a fast-moving fire and unable to evacuate.
Although I love ICF, I do not like ICF for wildfire areas because I think the outer layer of styrofoam would melt in the event of a serious wildfire, and most ICF uses traditional wood truss roof anyways. So I am really looking for a completely non-combustible building assembly which would have a high probability of surviving a severe fire with only minor damage. Insulation should be either non-combustible (like rockwool) or fully encapsulated in thick concrete so it can not burn/melt. I don’t want to rely on venting details to hopefully block embers from getting into the roof structure… I want a completely unburnable roof structure.
I have not found any examples of roof structures using pre-cast thermomass panels, or any fully non-combustible roof assemblies.
If you were going to build a cabin in wildfire territory, you only cared about ensuring survivability of structure and occupant in the event of an extreme wildfire, what building system would you use? Are there any fully non-combustible building systems that could give high-confidence survival in an extreme wildfire event?
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