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Dampness Issues in Houses

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Dampness Issues in Houses

by Pietro Scalise

Damp is predominantly the affliction of old houses and to a lesser degree poorly built new homes. It can spoil the structural integrity of a home as well that crucial pre-purchase open-home visit. It is the scourge of real estate agents since, armed with knowledge, savvy buyers can negotiate further to their favour.

Your chances of happening upon a suburban home with rising damp problems are quite high. Forty-five per cent of solid brick houses aged 70 years and over, and a quarter of houses aged 50 to 70 years have rising damp [The Age, Thursday 27 February, 1986, p.5].

It is highly advisable that if youre considering the purchase of a home, a thorough pre-purchase building inspection be carried out, firstly by yourself then by a qualified building inspector who will document and provide photographic evidence of damp. What you may interpret as trivial dots on a wall or innocuous spots of bubbling paint may in turn demand the introduction of a damp proof course (DPC) with substantial cost and disruption that were not planned.

There can be many categories of damp although rising damp is the most notorious.

Rising damp

This is caused when ground moisture flows upwards through a permeable wall structure, past faulty or non-existent DPC, through the pores in the masonry, whether brickwork, stone or concrete blocks. It seldom rises above 1.5 metres due to natural evaporation but may be pushed further upwards if the wall is sandwiched between two layers such as impermeable render or oil based paint. If rising damp is evident, repainting or re-rendering a wall surface without treating the problem at the root can only lead to rising damp travelling further up the wall.

A rise in the water table can cause rising damp on walls but often the problem can be caused by an unsuspecting homeowner who may build up soil as garden beds around external walls as part of general gardening or landscaping when paths around the perimeter walls may be inadvertently be built above a DPC or even cover weep holes, that let water out of a cavity, or worse perimeter wall vents. During renovations, adequate sub-floor ventilation must be observed. Often, external works such as external rendering can give way to bridging of the DPC, where the moisture is able to bypass the barrier.

The presence of rising damp causes some materials to deteriorate. Plaster softens; paint will bubble and peel; steel reinforcing will rust; nails will disintegrate and timber will rot. Unhealthy mould smells will be evident and insect pests such as termites will be encouraged to penetrate your home causing unspeakable damage.

Further, the presence of salts in the damp will cause a microscopic attack on the masonry materials. The salt crystals exerting pressure from within the masonry pores will cause the masonry to break down and spall off in layers.

It is a veritable vicious cycle. Hydroscopic salts are carried in the rising damp and as the dampness evaporates on the wall, salts are left behind on the surface that concentrate and in turn attract further moisture.

It is also a problem not to be taken lightly. In their 1999 Australian Housing Survey, the Australian Bureau of Statistics has found that 4% or one fifth of housing stock that required major structural repairs, suffered from rising dampness.

Rising Damp in Unrenovated Buildings

If a building hasnt been recently renovated, it is far easier to ascertain whether a problem exists or not.

Inside the house, paint is noticed not adhering to walls. Stains and mould spots will spoil the surface of walls. Render flakes away and salt crystals are evident, white and powdery. Skirting boards may be soft and rotting. A general musty smell overpowers a room.

Outside the home, the mortar between the brick or stonework will be inclined to crumble and fall away. A residual white powdery stain (efflorescence) noticeable on the masonry. On standing away from a house, noticeable at the base of a wall, will be a darkened tide mark, a sure sign that rising damp is taking place.

Rising Damp in Renovated Buildings

Houses that have been renovated for sale with an effort to cover signs of rising damp are more difficult to diagnose. If an owner has decided to treat a wall with waterproof render, the only reliable method is to drive masonry nails through the render and take a reading with a moisture meter. But this is not always possible or allowed.

A waterproof render is not a solution to rising damp and will fail at the expense of the new owner, usually by pushing the moisture further up on a wall. What is required is a horizontal barrier that will stop the rising damp.

For new owners that have unwittingly purchased a home riddled with rising damp, it can be a heartbreaking experience having to remove skirting boards, remove wall linings such as render (even if waterproof render) install a new DPC and replace the render. In some cases it can be a drawn out process lasting months.

Horizontal penetrating damp

This occurs when rainwater soaks through faulty walls; i.e. where mortar joints of brickwork are crumbling away. Bridging across, moisture can then travel to the internal face of a wall.


This is caused by inadequate ventilation, i.e. poor underfloor ventilation in timber framed floor homes; or large discrepancies between internal and external temperature or humidity.

Condensation is the most common cause of dampness in dwellings and is associated with unhealthy mould growth. A musty odour in damp houses is a tell tale sign of mould growth with spores that can give rise to many health problems. Condensation is not just limited to walls and floors but also the underside of timber framed floors in the sub-floor area and roof spaces.

The problem of condensation arises when moisture-laden warm air comes into contact with a cold surface. On an impermeable windowpane the water falls away but on a permeable surface, such as timber and walls, condensing water seeps into the material. In most cases, if not due to poor underfloor ventilation, installing a dehumidifier inside the home can resolve the problem.

Falling damp

This is a result of poorly installed roof drainage, predominantly leaking gutters, flashings or pipes.

Obvious signs that your home is suffering from dampness are mould patches high on walls which blister, stain and peel paintwork; soft, drummy or crumbling render on internal or external brickwork or stonework; wallpaper that peels from internal walls; salty deposits on walls and rotting floorboards.

The existence of damp problems in a house should not deter prospective buyers from purchasing their dream home. All types of damp, whether rising damp or a simpler condensation problem can be treated successfully. What is necessary though, is that the interested party be aware of the consequences so that repair works may be allowed for in their investment. In most cases then, a routine pre-purchase inspection costing a few hundred dollars by a qualified building inspector may save thousands in the long run.

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