The Lightweight Modern Queenslander
The solution for challenging, flood and cyclone prone sites
(Russell Brandon was asked to speak on the above topic at the Timber Queensland “High and Dry” Seminar in March 2010. This is an overview of the presentation.)
When we think of 2011 so far, two questions come to mind - “where next?” and “what next?”
Serious flood, damaging cyclone, devastating earthquakes and tragic tsunami, we’ve had it all so far and it’s still only March.
It may be that our world is going to continue to experience more and more widespread problem events. For designers and builders of structures that we want to survive for the long term this means we may need to change the way we do things. We certainly need to learn from what we have seen and think about what may happen in the future.
In Queensland we can break down our most serious events into three different types.
Overland flow flooding results from localised extremely heavy rainfall which is often channelled into spaces not designed to take the resulting volume of water. It can occur at what appears to be the top of the hill (at least to us at the bottom looking up) as in Toowoomba or at the bottom of the hill as happened in the Lockyer Valley.
Mainstream flooding results from more regional rainfall probably over a longer time period. It can result in safety releases from dams and involves slow moving large volumes of water. The main effected areas are river or creek floodplains.
Cyclones are a part of life in tropical areas. What we experienced with cyclone Yasi was something bigger, broader and stronger than we have seen in recent years. Some say that more severe cyclones and cyclones in more southerly locations will become common.
If there is one thing for us to learn from 2011 it’s that nature is no respecter of geographical location. In 1961 I experienced, first hand, a cyclone on the Sunshine Coast so I know cyclones can wander south, but I never expected one to head towards Mount Isa. We must never become complacent and fall into the trap of designing as if it “won’t happen here”.
As we saw in tragic circumstances this year, an overland flow flood will most often result in flash flooding with fast flowing water that can exert some very serious forces. This is the biggest threat to life and limb because it is often unexpected, happens suddenly and the resultant forces will be extremely damaging to anything in the way.
This can be an exceptionally high volume of water arriving very quickly.
I asked one of our more experienced Darling Downs members where all that water came from, he explained that when he first went to university in Toowoomba, the campus was surrounded by open space. It formed a sort of natural absorption/retention basin around West Creek.
A lot of development has occurred since then forcing all that water into narrower, deeper drains feeding existing waterways. The point of confluence of East and West Creeks was always going to be a trouble spot, according to my member. Nobody could predict just how much water would meet at that point.
So how can we do a better job of planning our developments?
I suggested to someone else that Toowoomba is at the top of the hill so where did all that water come from? I was simply advised “out of the sky, mate”.
It is most important for us to understand just what the water that falls from the sky wants to do once it hits the ground.
It is important that we let it follow as much as possible its natural flow path and this simply means maintaining the natural slope and contour of the land wherever practical.
As we look into what might happen in the future, we must come to the conclusion that we need to do all that is possible to maintain the stability of our hillsides. That means leaving the natural landscape untouched whenever we can.
It means that we should never ever take a sloping site and cut and fill a building platform simply to feed our obsession with slab on ground construction.
“A building should grace the landscape, not disgrace it.” Frank Lloyd Wright
Frank Lloyd Wright talked about buildings that work with their surrounds. He also said that a house should not be on a hill but should instead be of the hill, house and hill should be as one.
So what’s the best way to design a home that works with the landscape, including the overland flow path?
1. Take care with the footprint. That means, think about how the rain water wants to flow through the site naturally and use the location and shape of the building to allow the water to get to where it wants to be with a minimum of disruption.
The home which became known as Wright’s greatest design feat was Fallingwater. It was designed to straddle the waterfall rather than sit beside the river looking at the waterfall. We can use this as an inspiration to design houses that cause minimum disruption to the natural water flow.
It may mean that we need to do a little more research into what the natural overland flow is and take a little more care about the design.
2. Next, keep the floor level and its sub-structure above water.
This is, of course, just as important or more important on a flatter site as it is on a hill but where built on an overland flow path the floor level may need some consideration.
3. Where there is a danger of flash flooding, we must allow for the destructive forces which will be applied to the building by strengthening the sub-structure and the connections all the way from the roof top to the foundations.
If flash flooding is dangerous because it happens suddenly and unexpectedly, mainstream flooding gives us much more warning but can be just as destructive, (normally over a wider geographical area), through inundation.
We know that the force of the water when it’s made to flow between river banks can carry away pontoons, boats, even riverside restaurants and concrete walkways, but as it spreads out over flood plains, it slows and causes devastation by soaking everything in its path.
So how do we go about designing homes in the flood plain?
Before we start we must know where past floods have been then set a floor level that has sufficient free-board.
There are a couple of issues here.
First is the artificial height restriction of 8.5 metres. We know that in some existing housing in flood problem areas this just won’t be enough to allow owners to raise homes out of harm’s way. It’s good to see Brisbane City Council recognises this.
I hope common sense applies in other places and where new homes are to be constructed in susceptible areas.
The other issue is that if we continue with our obsession with changing the landscape to accommodate slab on ground construction, the flood heights will change.
One designer of a home in the fast developing western corridor did the right thing. He checked on the 1974 flood and set the lowest floor 1.8 metres above that level. In 2011 the flood height reached a massive 3.6 metres above the 1974 level.
Of course, people in older Queenslanders are prone to extend and many just want to raise the floor level and build in under. There may be better ways. One designer created a renovation for a home in one of Brisbane’s older riverside suburbs and chose to extend out rather than up. It survived the 2011 flood.
There are some things we can learn from this project.
This designer was aware of the 1974 flood level and made the lower floor around 300mm above that level. The easiest way was to use a raised timber floor.
In case the flood level does change we can consider making the lower floor “sacrificial” by using materials that can survive a soaking and by carefully selecting the use that will be made of the lowest floor. Don’t design the room to house the grand piano on that level.
We need to make sure that if we do need to scrap and rebuild the lower level, the structural integrity of the home remains intact.
One of the things that delays re-occupation of the home more than anything else is the danger inundation has on the electricity wiring. Maybe we should consider isolating power circuits to floor levels which may be in danger of inundation.
Contamination of services is another problem so we may be able to take steps to isolate the water and sewerage pipework during an inundation event.
And then there was cyclone Yasi.
When I ask designers in North Queensland why builders want to build in concrete block, I always get the same answer; “it’s the cyclones”.
There is plenty of evidence that many timber framed houses that endured the worst of Yasi remained structurally intact. In fact most homes, regardless of construction type, that had been designed to current building codes and constructed in accordance with the design came through the without significant wind damage.
Here are a couple of lessons we can learn from Yasi.
1. Lightweight timber modern Queenslanders can perform well in cyclones but designers must take care in detailing and specifying product, fixings and finishes.
For example specifications for windows and sliding doors must include the correct wind loading and detailing must show correct fixing details.
We learnt from cyclone Yasi that, during longer duration wind events, which this was, vibration becomes more of an issue. We know that sheet roofing now must undergo low/high/low testing to accommodate this but do we understand that vibration can cause nuts to come apart from bolts allowing damage to occur.
2. A message for builders is to build strictly in accordance with the plans and specification.
One failure we heard about a number of times was water penetration through louvres. In one case we looked into, the design called for a particular brand of louvre (Breezway) but the builder talked the owner into using a cheaper product.
The installed louvres “leaked like a sieve” while there were many reports of (Breezway Louvres) the specified product remaining perfectly waterproof – even in the Mission Beach and Cardwell areas.
A major concern in this cyclone was the storm surge. My enduring memory of Yasi is a home owner saying; “We had a Mazda in the garage. The garage door is gone and the back wall is gone. We can’t find the Mazda.”
Like designs for the floods we talked about previously, the modern Queenslander is ideal for surviving the storm surge. Keep the floor above the expected storm surge level and strengthen the sub-structure to withstand the forces involved.
Take home messages
Not only can the modern Queenslander be stylish but it can also stay high and dry regardless of what nature can throw at it.
The modern Queenslander works well with the landscape. It does not disgrace the landscape it will grace the landscape.
The modern Queenslander is liveable, sustainable and comfortable in Queensland’s great climate.
The modern Queenslander is strong and durable.