James Davidson of JDA Co., is an architect who has been specialising in disaster-resilient retrofits and architectural design solutions for over 20 years. Davidson is joined by Nick Wiesener, head of Disaster Management Australia and insurance advisor to national government.

This interview, presented as a four-part series, documents their discussion covering government policy, social, economic and insurance issues surrounding the response to the issue of flooding to homes in Australia, and culminates in recommended building solutions.

This frank discussion aims to add to the wider dialogue among the architecture community in New Zealand, and further highlight the urgent need to take action in defending our homes and livelihoods against climate change.

Flood resilient architecture (Part 2): The Australian response

Adrienne Miller (AM): What type of housing is hardest to retrofit and how do you address the less preferable housing stock types? 

James Davidson (JD): The obvious one is brick veneer, slab-on-ground housing in a flood plain. They’re practically impossible to elevate — although there are some interesting businesses who’ve popped up saying they can do it. But we do have developed solutions for how to retrofit those homes to make them easier to clean out. We’ve got principles across about eight or 10 different housing typologies, as well as for complicated mixed-typologies beyond that. They’re equally problematic — all of them — but the least problematic is the old Queenslander style that we have here [in Australia]. But that’s not suitable in New Zealand where it’s cold. That’s why I’m keen to come to New Zealand and figure out the differences in the built environment there. Because although we’ve developed principles for adaptable building within Australia, I’ve never worked within a New Zealand context. But in answering your question, it’s within an Australian context that I’m referring.

AM: Well at least now you might be able to get into the areas that were worst affected by the floods. What is a critical takeaway from an Australian context that could be applied here in New Zealand?

JD: One of my builders is a Kiwi and he’s been doing flood resilience work for years now. He and I have spoken at length about the different detailing approaches. The critical thing is in allowing water to flow through a home — and that’s primarily what we do. We accept water. That’s the idea. It’s wet-proofing. We’ve been down the path of looking at dry-proofing systems where you keep the water out, but that failed. We brought some materials in from the UK into the local Council program a few years ago and it just led to a level of complacency in occupants. 

AM:Can you elaborate a bit more for us around the complacency you saw that resulted from a dry-proofing approach? 

JD: It was a surprise. When these homes flooded and the doors failed, the homeowners got really grumpy and tried to sue the builder and tried to sue the Council. So it just proved to me that by talking to people about their flood risk and allowing the waters to flow through, they have to accept a certain level of risk. 

If they’re willing to stay in their home, they have to put a system in place whereby if there’s a warning that there’s going to be a lot of water, a lot of rain etc., then maybe they start to move their contents out, or upstairs. A lot of the clients that we’ve worked with pre- the 2022 floods actually started putting their property into a trailer and moving it to high ground because they knew there was a big risk coming their way. That’s part of the education process that goes along with the design work, which has proven really valuable. 

It’s also part of the reason why we get involved in doing assessments and reporting for Government because the whole process is designed to educate. It’s going into someone’s home and saying “let’s have a cup of tea, have a coffee, talk about where your flood risk is coming from, what levels, what return intervals we’re talking… These are the projected flood levels that we’re working to, so if we are going to be building back or retrofitting your home, maybe it’s the same cost to do something at a 300 millimetres level as it is to do to 1.2 metres”. We’re not only producing properties that are defendable, we’re also educating the homeowner as to why we’re doing the work. 

AM: There’s that old, well-worn Dutch cyclist joke: ‘There’s no such thing as bad weather, just bad clothing’. When does the weather or the location become so bad, that you can’t come up with a fit clothing or housing solution?

JD: Pre-2022, I would have given you a different answer to this. But I think I’ve been incredibly surprised by just how resilient some humans are. So that’s a very individual kind of subjective decision. 

AM: Humanity comes into it when we’re buying back homes in flood plains. 

JD: We’re buying back homes in certain areas of Brisbane that have 10 metres of flood risk, for instance, above ground level — maybe even more than that. And some people in these areas, while their neighbours are being bought back, others don’t want to be bought back, even though they’ve had two major events — three, to four metres beyond their roof line in the last 10 years — and they still want to stay there. Personally, there’s no way I would be wanting to stay in a flood-prone area. Some people are saying “I don’t want to be bought back because now I’m going to end up with like a beautiful park around my house. And, you know, I’ll go through it again. It’s fine, and we can bounce back”. So human resilience differs greatly amongst individuals. 8 

AM: Can I loop back around to the cleanability issue? What are the best building products and built form solutions that enable cleaning and timely re-entry? 

JD: Blackwater situations involving sewerage or pollutants— they’re the worst — it depends on the type of flooding and it’s different depending on whether you’re insured or uninsured. If you’re insured, you need a hygiene certificate which can be the reason people are kept out of their home for a year or more. 

We’ve had situations where a property has failed hygiene certificate three times and the insurers just won’t build back. Whereas the neighbour who’s uninsured — even though they’ve been through the same kind of situation — they’re cleaning up, spraying a bit of chlorine around the place and getting on with things. And so we’ve actually seen in many instances that it’s actually better to be uninsured, based on your ability to get back in your home. 

Now, in terms of materials, the best products consist of anything that is waterproof. In the last 10 years there’s been an incredible development in different material types. When we first started there was a very limited range, so we were restricted to rendered blockwork and grinding concrete floors and those kinds of things.

AM: What common building materials should we be avoiding in flood-prone areas? 

JD: Hardwood timbers are fine. Softwood timbers are really bad because obviously they’re a lot less dense. We’ve found hardwood timbers to survive and bounce back very easily. They don’t soak up as many nasties in terms of moisture.

We will paint a softwood frame with a mould-resistant paint, and line that with a sort of fibre-cement product and then seal the internal lining, because the theory is if the water can get in, then let’s try and make it easy for the water to get out.

We’ll also use paint to wet-proof when we’re retrofitting a brick veneer home. There are a lot of gaps in brickwork, which means you can’t keep the water out of the external cavity, so we just accept the fact that it’s going to get wet.

We will try a lot harder to keep the water out of the internal walls. In some instances, we propose removable panel systems if we’re not comfortable that we’re going to be able to waterproof it properly. Carpets, plasterboard and pine framing are not good materials due to their capacity to hold moisture.

There is this thing called bracing plywood and that goes through a flood quite well. I’d be suggesting New Zealand instigates the use of structural bracing ply in a flood prone areas rather than plasterboard.

In terms of insulation products, we use rigid-foam insulation within a wall system rather than fibreglass and other absorbant insulation methods. Again, anything that retains moisture is an issue.

Read: Flood resilient architecture: Part 3 - The Australian response