Surviving an intense canopy fire in the South Coast fires 2020: recount and design decisions

On New Year’s Eve the fires that swept through Runnyford NSW, in the South Coast fires, severely burned our bush block along the Buckenbowra river. Amongst the post-apocalyptic scene, our small house stood untouched. Many friends congratulated us on this incredible outcome, but to us it was not a question of luck. When we started building our off grid house, exactly 12 months ago, fire was our biggest consideration. We ‘d read about the massive 1905 fires, that burnt to the ground many houses around the area, including the Balcome’s homestead on our property (never rebuilt). Scouting our land, we pieced evidence of other more recent bushfires, so we assumed that fires would happen, and there was nothing we could do to avoid that. This was critical in our decision making. At the same time, no one had lived there for over 100 years; the forest had grown dense and full of wildlife and we loved that, so we wanted to have minimal impact on the land.

We referred to flame zone building Bushfire guidelines and my working knowledge as an architect of fire regulations on commercial buildings. We had no access to water, no dams and no water tanks installed, so sprinklers were not part of the initial design.

Though we were expecting a fire at some point in the future, it was not until October that we perceived an imminent threat and rearranged our building sequence to have the house safe by the beginning of the summer. The land had dried up and the tree canopies began to look affected. I was building the house with my three sons and the occasional friend, on weekends and holidays and time was running short. A sense of urgency fell upon us. We stopped work in the bathroom and focused on finishing the fireproofing.

The house was designed to be built quickly. with a very restricted on-site presence and using readily available tested materials to keep our costs low: fibre cement sheets, steel stud frame, Colourbond steel, insulation and off-the-shelf hardwood windows and doors.

Key to our design intent was to capture our surroundings as much as possible, so the tension between openness and fire safety was a challenge. There was no point in building a home where we would not feel amongst the trees, and conversely, there was no point in building a largely glazed house if we compromised its capacity to resist fires. We settled for sliding door panels in the living areas, using a ratio of window to wall that would allow us to install steel fire shutters . A 5.5 m opening to the North and a 2.4 opening opposite to it on the south façade achieved the transparency in the landscape that we looked for. Yet, with the shutters closed the house sat like a hermetic box in the landscape. As a bonus the steel added more articulation to our fibre cement façades, providing a change of materials and planes.

The house was designed as two parts, the part which you see in the photos is the fireproof core, approximately 100m2 which is mostly built; and part 2 as yet unbuilt, is a large external roofed living area to the east and an entry area with stone walls to the south.

The construction of the fireproof core, that so successfully dealt with the fire, was based on a one-hour fire rated wall, made up of fibre cement sheet on a steel stud structure, with R2.8 insulation and plasterboard inside. Over the rafters we used a steel sandwich of a colorbond roof and zincalume ceiling separated by lightweight steel, packed tight with R4.1 insulation. To make fireproofing easier, we had no eaves. A structure for deciduous green-eaves and some roofed pergolas would be added in the second phase of construction.

In all of this, however it was the detail of the construction that was critical. The fibre cement cladding, for example, lapped over the hardwood window frames to provide an additional buffer against radiant heat. All gaps were kept to 2 mm and filled with intumescent filler, which expands when exposed to heat. A simple but equally sealed Colourbond skirting was built under the house to stop the fire getting under the floor and into the plumbing.

The level of insulation proved adequate to prevent any heat damage to the inside of the house and contents. The steel fire shutters protected both the hardwood frames and the glass. We had no broken glass, no scorching and no melted plastic inside.

Another interesting and yet simple decision to make, was to ensure that no cabling or plumbing was run in the external wall cavities or ceiling, to avoid radiant heat damage. All electrical cables and pipes were run through internal walls and under the house.

It was a big effort by everyone and a huge push at the end by the boys and myself to get the fire shutters in place, before the fire came through. The shutters and gaps were fire sealed and completed literally three days before the fire came through. The fire had jumped the Kings Highway and was threatening us from the west. We did not hang around.

The first person into the area was a friend, who’s seen many fires working with post-fire injured wildlife, and who described to us as “I’ve never seen such an intense and extensive burn”. The fire approached the house through the ridges as a canopy fire, and the wind must have been ferocious, leaving the few remaining casuarina stumps bent right over. All the timber in contact with the ground or old dead trees and posts have burnt out almost completely, leaving behind lines of fine ash on the ground irrespective of timber type or size. For me this dispels the idea that large hardwood sections will char but survive, at least in a fire as intense as this. The only timber on the ground now are trees that were green at the time of the fire and have since fallen over.

Currently a discussion has started about the feasibility of building within a forest and whether we should simply clear more and more to make way for safer houses. All I can say is that we built our house to resist a bushfire, and it did successfully with a cost effective, fast to build and reasonably open design, despite the unprecedented intensity of this fire.

Now we have a long journey ahead supporting our land to regenerate and consolidating and sharing the lessons from this experience.

Thank you to all those who made enquiries about our house in the forest.

Posted by Alastair Falconer