KEY POINTS:
The drought is starting to affect urban homes - leaving some house-owners with repair bills of tens of thousands of dollars.
Walls are cracking, foundations are moving and the ground is subsiding, particularly on the North Shore.
Sewers are blocking for lack of ground water and tree roots are being exposed as bone-dry soil subsides.
Even mowing the lawn has become a hazard - a North Shore resident says he ruined his mower when he struck newly exposed roots.
Nick Rogers, an engineering geologist at Tonkin & Taylor, said startled owners were able to see daylight through severely damaged walls, ruined by ground disturbance caused by low soil moisture levels.
Cracks were appearing inside and out, he said, and ground had settled up to 10cm in some cases.
In some cases, builders had advised partial demolition which left homeowners horrified.
But Mr Rogers said major building works might not be necessary.
In many cases, subsidence could be rectified by watering the affected area.
"We've had situations were people have got in builders and they recommend demolition when they could have repaired it with the hose."
But Beca Infrastructure's chief geotechnical director, Do Van Toan, said watering around house foundations could damage the structure and cause ground heaving or swelling.
Shallow housing footings would suffer the most in dry conditions, and clay sewage pipes - common before the 1960s - were at risk of being invaded by water-seeking tree roots.
Geotechnical engineer Gareth Williams, of Engineering Design Consultants in Birkenhead, said: "We are seeing structural problems with house foundations not being deep enough.
"The soil is drying out and the corners of buildings are cracking away if they are brick veneer-type buildings."
He said a corner of one building had "just broken off. I would say quite a few insurance claims will be going in, especially with the older properties.
"The sun just dries the soil out and the soils in New Zealand tend to dry out and wet up again quite quickly.
"Repair costs will vary. You could be looking at tens of thousands."
Ian Norrie, of North Shore firm Uretek, which uses resin injections to strengthen foundation ground, said: "In Remuera we have had 25 or more calls in less than a week and I have been to a heritage home in Remuera looking at exactly this type of problem. The cost of fixing it ranges from around $5000 to $12,000.
"Substantial areas of Auckland have reactive clays which shrink considerably in summer as they dry out and expand again in winter.
"Eventually there's a settling which puts stress and strain into a house and ultimately it starts to crack."
