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How to design your house for fire resistance and sustainability

Durimbulhouse by Matt Goodman Architecture Office. Photography: Paul Hermes

If anyone is any doubt this is a climate emergency, last week’s announcement by the NSW Rural Fire Service that bushfire season has been declared two months ahead of the usual date should sound the alarm bell.

As of 1 August, 12 Local Government Areas officially entered the Bushfire Danger Period due to continued hot dry conditions: Armidale Regional, Bega Valley, Eurobodalla, Glen Innes Severn, Inverell, Kempsey, Mid Coast, Nambucca, Port Macquarie Hastings, Tenterfield, Uralla and Walcha.

Some of these communities are already running out of the key weapon in the fight against fire – water. As ABC reports, Tenterfield has had to procure an emergency desalination plant to ensure sufficient potable water supplies. Armidale City Council is trucking treated potable water to Guyra to top up its dwindling town reservoir.

The official bushfire danger season in NSW historically starts on 1 October, but as the NSW RFS noted in its announcement, fires have been occurring much earlier than tradition would predict.

NSW RFS acting commissioner Rob Rogers says now is the time for residents and land managers to start preparing for the threat of bushfire.

“Last season we saw more fires in July and August then the whole of summer combined…recent fires on the Mid Coast and in the Hunter region have shown that bush fires can strike at any time and it is vitally important to be prepared.”

Queenslanders have also been put on notice about fire risk. The state government released a new State Heatwave Risk Assessment report in June 2019 that highlights the need to prepare for heat-related natural disasters of greater intensity and frequency.

In a forward from Queensland Fire and Emergency Services chiefs it notes, “Our collective ability to assess and more deeply understand the impacts of climate change on current and future natural hazard risk is the first step towards the ongoing development of resilience in the face of more and more intense natural hazards.”

Bushfire is identified as a “consequential hazard” of heatwaves, as shown in the case study of the catastrophic 2018 fires in the state. The conditions at the time including elevated temperatures around the clock, low humidity, a dry season and strong westerly winds had never been experienced before – and the resulting fires were unprecedented in the state’s experience.

The key messaging from the Queensland, NSW and other state emergency experts is planning for disaster starts now.

Cities also at risk

Fires last summer in places like Blacktown in Western Sydney and the 2003 Canberra bushfires are also a stark warning that it’s not only rural and regional communities that need to be worried – our big city suburbs are also potentially at risk.

Designing for fire can also be designing for sustainability

The good news is there’s a synergy between designing and building for bushfire resilience and designing and building for sustainability.

CSIRO Bushfire Urban Design research leader Justin Leonard says the current requirements of building codes and other regulations for building in areas designated as high bushfire risk are  “skin-deep”.

The focus on elements such as the façade materials and final finishing details to reduce the potential for ignition, he told The Fifth Estate. But these don’t make a building “inherently robust”. They can be compromised through by wear and tear and modifications.

Resilience needs to consider the whole lifecycle of the building and go consider the systems involved – the roof system, wall system, floor system and subfloor system.

And here there is a “very heavy overlap and synergistic opportunity to think about energy-efficiency, resilience and bushfire”., Leonard says

“By and large [these things] are quite aligned.”

A systems-based approach can deliver high levels of energy efficiency, better odds of bushfire survival of both the building and its occupants and recyclability at end of life.

“Leave soon” is not always an option

While much of the public-facing information about bushfire survival focuses on the “leave soon” messaging, that is not always an option. Personal bushfire planning is flawed if it focuses solely on “not being there at the time”, Leonard says. 

Homes and other buildings need to maximise the chances of survival for occupants if roads are cut, fires appear too suddenly, or there’s no transport for escape.

Making a building fire resistant

1. Minimise “exploitable details”.

Design a roof that minimises the chances a fire can start in the roof cavity, where internal smoke alarms may not detect it.

That might mean not having a roof cavity at all, or having non-combustible roof framing, choosing a tight-fitting roof over tiles or choosing non-flammable insulation like rockwools, natural wool or fibreglass.

Insulation

Wall and ceiling insulation should be non-flammable. The spray-in foam polyurethane insulations perform well thermally, but they are both potentially flammable and can off-gas toxic fumes when exposed to heat.

A benefit of packing walls with insulation is both improved thermal performance generally and also designing out cavities where a fire can potentially take hold.

The walls

Earth walls such as rammed earth, compressed earth or mudbrick, and also rendered hay bale walls, can be excellent protection – and they perform brilliantly for thermal comfort, low embodied carbon and acoustic insulation.

Double brick

Double brick will outperform weatherboard or brick veneer on a timber frame on both energy and fire protection.

Asteel frame may be a safer choice than pine.

The NASH Standard

There is now a Deemed To Satisfy provision in the National Construction Code for steel-framed houses designed and built according to the NASH [National Association for Steel-framed Houses] Standard.

Justin Leonard was part of the CSIRO team that contributed to the development of the NASH standard.

One of the experiments saw a test house resist every flame CSIRO could fling at it. Another construction approach tested by the same team, the “Joost House”, which used magnesium oxide board over straw bale, also proved fire-resistant. MgO board is also a carbon-positive material.

The external temperature reached a scorching 1000oC while inside the house was a cool 35oC. Watch the video of the fire test here.

Windows and doors

Window glazing should be a high-performance toughened glass. Double-glazing is not particularly advantageous compared to toughened single glazing – but ordinary float glass won’t be a great choice.

Window and door frames should be part of the whole wall systems, and each element selected and installed to reduce ignition potential or gaps that allow ember ingress.

Air tightness

Airtightness and quality of finish for fire resistance overlaps with overs energy efficiency and thermal comfort.

Gaps and cracks can allow embers and smoke inside, as well as make the HVAC work harder all year round.

Maybe add “fire safety” to the already long list of reasons blower door testing should be business as usual for dwellings.

However, Justin Leonard notes that if the wall, roof and floor systems have been designed well with levels of redundancy, they can “handle a bit of shoddy workmanship and poor housekeeping” without compromising safety.

Ember attacks

He stresses embers are particularly important to plan for, as more than 90 per cent of homes lost in a bushfire are lost because embers moving ahead of the fire front were able to exploit ignitable materials and start a spot fire.

There’s something in that for planning and lot design to consider, as the vulnerability of any home is also influenced by the vulnerability and proximity of the houses next door.

Exits and escape paths

Doors and exits are another potential weakness. If part of the plan is being able to escape the home, decking, stairs, facades and doors that are combustible can prove a major threat to evacuation.

Materials inside

Materials inside a home can also pose a risk if they are toxic when heated or burned, so non-toxic paints, wall linings, floor coverings and other materials are important.

Gas and gas bottles

Gas bottles have a nasty tendency to explode in a fire, and in general, mains gas connected to a home is another weakness that can be designed out. Not only can a gas meter or the pipe into it rupture and fail, in many new buildings gas runs through plastic piping inside the walls – and it can melt, releasing the highly-flammable gas inside the walls.

“It’s really obvious sign to take gas out of the equation. It comes up time and time again,” Leonard says.

Electric home is more resilient

An all-electric home, with an EV, solar panels and either home battery storage or an ability to use an EV’s battery to draw power will be more resilient. It is not uncommon for mains power supplies to be cut during a fire emergency – or during a heatwave that precedes one – so having the ability to operate independently for energy is a plus.

Rainwater tank

The home rainwater tank also comes into its own, as mains water pressure can be vastly reduced where it is being used by firefighters. Grey water storage on-site can also potentially be an asset.

You can also install a roof sprinkler system supplied by the tank.

Home automation

And the final piece of the protection picture – smart home automation systems.

These are a known to be an asset for maximising the benefits of rooftop solar, so appliances can be operated while the occupant is elsewhere but the sun is delivering free watts to the home.

In event of a bushfire warning, these same systems can be used to switch on any protection systems such as irrigation and sprinklers or shutting protective awnings or blinds no matter where the occupant is at the time.

Plan A

In a nutshell – Plan A is to go for “everything passive” that can protect a building and improve performance; and plan B, where active systems are in place, make them activatable when the occupants are not onsite.

It’s a win-win – a more sustainable lifestyle at home, and improved resilience to bushfires, bringing together both mitigation of climate change through reduced household emissions and adaptation to increased fire risk and other heat impacts.

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