Bushfires 2019: Analysis of a total loss, lessons learned

Bushfires 2019: Analysis of a total loss, lessons learned

Sadly, a building designed by Envirotecture, and owned and built by one of our close friends, succumbed to the eastern flank of the massive Gospers Mountain fire in early December.

The only building to be lost in this part of Laguna, near Wollembi, there are some lessons to be learned, the first and foremost comes from David and Carol, the property owners, who said “Nobody died, and while it’s certainly sad, the only loss is ‘things’ and they can be replaced.”

That’s very true, although when he and I walked through the surrounding bush, we discovered the loss of biodiversity – especially some of the mature trees – is quite severe in places. Recovery will be slow and uncertain given the declining rainfall in the lower Hunter Valley.

But there are some good lessons to be learned about bushfire resilience in building design and construction.

THE BUILDING – CONSTRUCTION:

Built between 2003 and 2014, to AS.3959-2001 (the old bushfire standard) Level 2 Construction (no longer applicable, approximately equivalent to BAL-19).

Slab on ground, timber framed walls, Colorbond cladding, aluminium windows & doors, metal fly screens, EPS foam sandwich panel roof, tallowwood and ironbark columns.

Deck between shed and part way around house, elevated on hardwood piers, bearers and joists, blackbutt decking.

FIRE EVENT & INTERVENTION:

Gospers Mountain fire moving from North-west through Yango National Park towards Laguna and Wollembi.

Massively wide fire front, biggest on record.

Local fireys deployed elsewhere, interstate fireys looking after this part, did a great job on all other houses in the valley, but this one is visually concealed from the road and they probably didn’t even know it was there – so it was on its own, unattended.

It had been tidied up, cleaned, and the tanks had 80KL of water in them.

But no-one was there to run the pump.

IGNITION POINT/S:

Two likely points of ignition, uncertain as to which one happened first:

• timber decking: in spite of being on the approved fire resistant list, enough embers landing on blackbutt without being extinguished will cause ignition. One the deck was burning, the two rooms that were built on timber piers would have burned. The ironbark columns may have transmitted fire to the roof – but these were still standing and had self-extinguished, so this is less likely.
• EPS cored SIP roofing: not BAL rated (new ARC-Panel product uses PIR foam and rated to BAL-40), it is likely that embers got in through flashing gaps and immediately ignited the EPS core which is quite flammable. One more reason to eliminate EPS from our palette of materials – PIR foams would self extinguish.

RESULT:

Total loss, including the top 25mm of the concrete slabs bursting off, so they are probably a write off too.

Poly rainwater tanks melted, all water lost. Top of septic tank melted.

Aluminium window frames melted, liquid aluminium ran across ground. Glass melted. China coffee cups survived, as did the slow combustion heater. Kubota tractor with 200 hours on the clock now charred iron, etc.

WHAT MIGHT HAVE BEEN?

It would have been easy to extinguish the fire on the decks. The EPS cored roofing may have been very difficult, and risky in terms of falls and exposure to flame. So the buildings may have been unprotectable in the end.

NEXT TIME:

Given it is not permanently occupied, like our Mudgee Hempcrete House we would design it to be a hybrid BAL-40 and FZ structure, beyond code minimum requirements.

Large shade/fire awnings (not FZ rated) to the east, west and north, over BAL-40 glazing.

And not any EPS anywhere, and no exposed timber.

Inex decking would have been ideal, but another cementitious sheet decking will suffice, over steel frame.

The building frames can be timber again, as these are sufficiently protected by the cladding, and Colorbond is still the best cladding choice. Roof overhangs supported on steel outriggers and batten overhangs.