Rising damp: The scourge of old homes

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You’ve found the ideal new home – a beautiful established terrace and then comes the shock.

The building and pest inspection reveals rising damp.

What should you do?

You’ll often be able to tell a home has rising damp when you enter, because there’s a tell-tale sign of a with a musty odour.

Fact is, a high proportion of older buildings are affected by rising damp to some degree or another.

Rising DampAlthough rising damp can affect any brick house, older homes with poor underfloor ventilation in Sydney and Melbourne are most at risk.

Rising damp occurs when moisture from the soil surrounding the home finds a way into the structure of your home creating damp conditions that allows mould to thrive.

The moisture can also draw up salt from the ground, which crystallises in the bricks and causes plaster to flake and paint to blister.

Known as efflorescence, in severe cases it can even erode masonry and cause significant damage if left unchecked.

What’s causes rising damp?

Most houses are built with a damp-proof course between the foundations and the walls to prevent moisture absorption, but in older houses these are often damaged and in some cases were never installed in the first place.

This allows ground water to rise up through the bricks and mortar of a building by a process known as “capillary action.” It’s a bit like the way that oil rises up through the wick of a lamp.

Damp Proof Injection CreamHow high the water rises depends on several factors including the efficiency of any original damp proof course, the volume of the water supply, evaporative conditions over the wall surface and humidity.

What’s the treatment?

Treatment of rising damp is known as “damp-proofing” or “damp coursing” and typically involves stripping any plaster that’s damp off the wall, then drilling a line of holes along the wall at base level and injecting a silicone solution into the wall which penetrates to create a permanent barrier in the wall.

Then the walls are replastered using a salt retardant render.

Person Showing The Wall Covered With LichenHow much does it cost to repair?

It is difficult to get a “ballpark” quote for damp proofing, as it is notoriously tricky to diagnose the source or scale of damp related problems.

Every job is different and has to be assessed by a damp proofing professional, but a rule of thumb is to budget about $300 per metre

This means a terrace house with significant rising damp issues could cost up to $10,000 to repair, but the cost could be triple this in a severe case.

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