Flooded in 2018, damp ever since? What the water actually did

Rising Damp Hobart is asked about the 2018 flood more than any other single event, so it is worth setting out what actually happened. On 10–11 May 2018 a line of thunderstorms sat over Hobart and the Wellington Range. The city recorded 128 mm of rain, a third of it between 10.00pm and 11.00pm on the Thursday. 236.2 mm fell on kunanyi and 226.4 mm at Leslie Vale. The Hobart Rivulet broke its banks and flash flooding reached the Hobart CBD, Salamanca, South Hobart, Sandy Bay, New Town, Blackmans Bay and Kingston. The event is recorded as having an annual exceedance probability of less than one per cent — the sort of rainfall that is not supposed to happen in a lifetime. Insurers received almost 8,800 claims, with private property damage over $99.7 million and a total bill of more than $137 million.

Why this matters years later to a wall

The visible damage was repaired a long time ago. What is harder to see is what happened to the ground. Water that arrives that fast does not soak in evenly — it runs downhill, ponds against whatever stands in its way, and charges the soil around and under the footings. A wall does not care whether the water in the ground beneath it came from a storm or from a leaking downpipe. It draws it up either way.

Brisbane has the same problem after a river flood, but it resolves differently, because a Queenslander sits on stumps over a ventilated subfloor and a Brisbane summer is hot enough to drive the moisture back out. A Hobart cottage is usually solid masonry standing on rubble or slate footings with no cavity and often no subfloor at all, and the drying season here is short. That is the whole difference, and it is why a flooded house in Hobart can still be wet at the base years after one in Brisbane has dried.

The salts are the part people miss

Flood and stormwater carry dissolved salts. Those salts go into the masonry with the water, and they stay when the water leaves. As the wall dries they travel to the surface and crystallise, which is the white bloom on the stone and the reason render and paint keep lifting no matter how many times they are made good. A wall can be structurally dry and still be shedding its finish because of what the 2018 water put into it. Treating that is a different job from installing a damp course, and an assessment should tell you which of the two you are looking at — or whether it is both.

Flooding, lateral damp and rising damp are three different diagnoses

Hobart produces all three, frequently in the same house, because the city is built on a slope running down off a mountain to an estuary. Anyone who quotes a damp course without first working out which of the three you have is guessing, and a damp course will not fix the other two. That is the single most useful thing on this page.

Find out whether your address floods

You do not need us to answer this, and you should not take anyone's word for it — the mapping is public. LISTmap carries statewide flood mapping: search your address and zoom in to see modelled flood depth for the 1% AEP, 2% AEP and projected 2100 scenarios. The Tasmania SES strategic flood maps explain what those scenarios mean, and the SES publishes plain-language guides by area — the South Hobart flood guide is the one most people here want. Where a council has done its own study the detail is finer, so check the City of Hobart flood risk and maps as well.

A property that shows in the mapping is not a property with rising damp, and plenty of houses with rising damp have never seen a flood. The mapping tells you about one possible source of water. The assessment tells you what your wall is actually doing.

Will insurance pay for it?

Ask your insurer, not us, and ask in writing. What is worth knowing before you call is that policies generally treat a sudden event and gradual deterioration very differently. Damage caused by a flood may be covered; damp that has developed slowly over years is the kind of thing most policies exclude, whatever set it off. This is one reason the date things started matters, and why it is worth writing down what you remember about 2018 before that memory gets any vaguer. We are not insurance advisers and nothing here is advice about your policy.