How a bushfire can destroy a home


Douglas Brown, Western Sydney University

Ten years after the devastation of Black Saturday, building design has largely been unrecognised as an area worthy of research. We have advanced our knowledge of the materials used in the construction of homes in bushfire-prone areas but we continue to use the design model of the suburban home.

This needs to change. An initial starting point is to consider the way previous bushfires have damaged and destroyed buildings.




Read more:
Where to take refuge in your home during a bushfire


Elements of a bushfire

A bushfire has five different elements: smoke, wind, embers, flames, and radiant heat (the latter two are collectively called the “fire front”).

Smoke and wind are usually present throughout a fire, but are particularly high when the fire burns at its most intense levels. Depending on the type of vegetation burning, isolated flying embers may arrive hours before a fire front. Intense ember attacks usually occur 15-30 minutes before a fire front arrives, and may persist for up to 8 hours after the fire front moves on.

Radiant heat at a level that makes it impossible to survive outside will persist during the passage of the fire front, which may last anywhere between 2 and 15 minutes. However, if consequential fires are ignited by the main fire front, the radiant heat may remain at non-survivable levels for much longer.

The smoke of a bushfire reduces visibility and can turn a bright day into night. A change in wind direction can renew a threat residents thought had already passed them.

How will a bushfire attack your home?

Most people would expect that the most destructive element of a bushfire is the fire front, but rather surprisingly that’s not the case. Ember entry and associated spot fires, rather than direct flame contact, accounts for 75-80% of homes destroyed by bushfires.

Embers can be large strips of burning bark, or a tiny spark as small as a pinhead, and depending on wind speed these can travel up to 10 kilometres ahead of the fire front.

Australian research over the past 75 years has revealed more than 20 different parts of a house and its surrounding area that are vulnerable to bushfire attack. Much of this knowledge has now been incorporated into a recently updated Australian Standard: Construction of buildings in bushfire-prone areas.

These guidelines aim to reduce the vulnerability of each part of a house, and thus make the structure as a whole more resistant to bushfire damage. The Standard applies across Australia for new homes and renovations.

The known building ignition points

The known weak parts of a building are referred to as the “building ignition points”. Several are considered below:

Roof cavity

In domestic homes the roof cavity is the large open space under the roof and above the ceiling. Embers in this space can cause fire to spread rapidly, making the whole building vulnerable to ceiling collapse.

Any gap in the roof, such as a poorly secured tile, can allow flying embers to enter. The burning crown of a nearby tree, pushed onto a roof by high-speed winds, can also ignite the house.

When people choose to shelter in their bathrooms they often forget the ceiling is particularly vulnerable there. It’s difficult to access a roof cavity with a fire hose, and extinguishing embers and fire invariably damages electrical wiring, plasterwork, and home contents.

Regular inspection and maintenance of roof elements can help reduce ember entry. Avoiding trees close to your house, and removing any overhanging branches, can also help reduce this bushfire risk.

Gutters

Overhanging trees can cause compacted leaf litter to build up in gutters. During a bushfire flying embers land in this material, catch alight and spread flames to combustible parts of the roof structure such as wooden facia boards, rafters, roof battens, and eaves.

It’s a good idea to clear out your gutters each year as part of seasonal bushfire preparation. Some people choose to wait until a bushfire is approaching to do this, but going onto your roof for the first time in semi-darknes while embers are flying at you can put you at risk, and endanger your life.

If you’re building a new structure you can consider extending the roof line and having a water collection system on the ground to remove the need for gutters.

Vents and weep holes

Together vents and weep holes allow for fresh air to pass through a building and for excess moisture to leave, reduce condensation and mould. They are necessary for our comfort and health, and maintaining the integrity of a building.

However in a bushfire these types of external openings can allow flying embers to enter the building and start spot fires. Having steel or other non-combustible mesh with small holes in front or behind vents and weep holes can reduce the bushfire risk while still allowing air and moisture to pass through.

Subfloors

Often houses constructed in bushfire-prone areas are built on a sloping block of land. The area under the building (the subfloor) is left open rather than being enclosed, and combustible materials are often stored there. The danger is similar in scale to embers in the roof cavity. When embers or flames take hold in this subfloor area they can spread under the entire building and allow the fire to move up.

Plants and mulched garden beds next to the home

Garden beds and timber steps near a house are a potential danger during a bushfire. Plants with dense foliage can burn intensely and cause radiant heat damage, cracking and imploding nearby windows and glass doors.

Garden beds which have been recently mulched can trap flying embers and spread fire to timber subfloors. It’s much better to have a non-combustible paved area next to your home, with pots containing either succulents or plants with thin foliage.




Read more:
How can we build houses that better withstand bushfires?


Deciding whether to stay and defend a home or leave early is a difficult and contentious choice. Hopefully, knowing more about some parts of your house which are most vulnerable to bushfire attack will make that decision easier.The Conversation

Douglas Brown, Casual Academic, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Comic explainer: forest giants house thousands of animals (so why do we keep cutting them down?)



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Wes Mountain/The Conversation, CC BY-ND

Madeleine De Gabriele, The Conversation and Wes Mountain, The Conversation

Giant eucalypts play an irreplaceable part in many of Australia’s ecosystems. These towering elders develop hollows, which make them nature’s high-rises, housing everything from endangered squirrel-gliders to lace monitors. Over 300 species of vertebrates in Australia depend on hollows in large old trees.

These “skyscraper trees” can take more than 190 years to grow big enough to play this nesting and denning role, yet developers are cutting them down at an astounding speed. In other places, such as Victoria’s Central Highlands Mountain Ash forests, the history of logging and fire mean that less than 1.2% of the original old-growth forest remains (that supports the highest density of large old hollow trees). And it’s not much better in other parts of our country.

David Lindenmayer explains how these trees form, the role they play – and how very hard they are to replace.




Read more:
Mountain ash has a regal presence: the tallest flowering plant in the world



Wes Mountain/The Conversation, CC BY-ND



Read more:
The plan to protect wildlife displaced by the Hume Highway has failed



Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation and Wes Mountain, Multimedia Editor, The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Site is Moving House


There are some massive changes happening at kevinswilderness.com – it will soon not even be called that. The name of the site will be called simply ‘Kevin’s Wilderness and Travels and will be hosted on WordPress.com. The domain name will probably be disposed of, by simply letting it slip off into history.

The move has come about because of the dramatic rise in hosting costs – which jumped greatly after the hosting company was sold to another. It did concern me at the time that a major price rise would be on the way. So the rise has arrived as expected and I’m now moving on. I love the WordPress.com platform, so the move won’t upset me too much at all. Being able to have ‘kevinswilderness’ in the site name has been a great bonus also, as it will mean that previous site visitors won’t find it
too difficult to remember.

WordPress.com offers the opportunity for so much more social interaction with visitors to the site – especially through comments being available on every page hosted there. Expect more photos and videos at the new site, with these to be hosted at Flickr and YouTube respectively. There should also be opportunities for chatting on site (via a widget or a link to Pip.io), forums, etc. The move is an exciting one for furthering the capability and usefulness of the site.

Work is already well under way and I am hoping that the move will provide new stimulus to improve the site, as well as add new features along the way. The social network hosted at Grou.ps will become a more important associated site and I am hoping to try and promote that more and more. I may however look at some other bushwalking/camping social networks that are out there too – perhaps they will provide a better enhancement to the site. Time will tell.

Please visit the new site and add it to your bookmarks/favourites – the old site has only a month or two to go before it ends forever.

The site is moving across to WordPress.com at the following address:

http://kevinswilderness.wordpress.com/