When you're spending many thousands of dollars on a new home, a few hundred dollars spent on a pre-purchase home inspection is a good investment. With a comprehensive list of defects, you can work out a repair budget and you may even be able to renegotiate the sale price of the home.

There are a few things you can look for yourself to narrow down the field before calling in a professional. You'll only need to be armed with a long-shanked screwdriver, spirit level, ladder, torch, binoculars, overalls and gloves.

Any house or unit could have major defects although the older the building the more defects are expected. Start by looking at the general appearance - a home which has been looked after is more likely to be in good condition.

Tree roots

Trees are an essential part of the environment - but not when they're growing right beside a home. The roots of the more vigorous species invade sewer pipes and reach under the floors in search of moisture. Over time they can lift footings and cause significant cracking in walls.

Bowed walls

Check corners are straight with a level. Sight along exterior walls from each corner to check for bowing.

Large bows in walls of cavity brick homes could be the result of the brick ties rusting through, leaving the inner and outer walls unsupported. Walls may need rebuilding.

Out-of-square or bowing walls in timber homes may have decayed or termite-infested framing or be poorly braced, both major repairs.

Cracks

Cracks are not uncommon in houses and it is important not to over-react to a few small cracks.

If there is a definite pattern of many parallel cracks, you can stick your little finger into a crack or the two sides of a crack are out of line, have an engineer check the home before purchasing.

Older homes were often built on shallow brick or stone footings on unstable soils with high clay content. These soils expand and contract with changes in moisture content, leading to hexing in the building, which in turn can lead to major cracking.

Lintels, arch bars

Old steel lintels rust over time and expand in size, with the power to lift brickwork. This leads to stepped cracking over openings. Replacement of lintels can range from a few hundred to thousands of dollars depending on size, access and complexity

Roof problems

Don't get on the roof itself, as most have a dangerous slope and the roof covering may be brittle. Use binoculars to check the roof from the ground, looking for broken or displaced tiles, cracked and missing bedding under the ridge and hip capping, loose flashings and rusty metal decks or valleys.<

If you have a ladder, prop it against the roof edge to have a look from gutter level. Check flashings are in place around chimneys and where roofs or dormer windows penetrate the roof line. If they look corroded or dislodged, roof work will be needed.

Check the roof pitch is sufficient to allow rainwater to drain easily. If a tiled roof seems to beat a slope you would expect only on a metal roof, chances are it leaks. Repitching a roof is expensive.

Wavy roofs often show the timber structure underneath is not sound or has spread.

Rising or salt damp

The older the home the more likely it is to have rising or salt damp. Over many decades the damp proof course, which is built into the brickwork, deteriorates to let moisture rise up the porous masonry by capillary action.

Inside the home, look for damp patches, stains and salt patches low on walls, often hidden by furniture. Damp rarely rises more than a metre up the walls and slightly higher in corners. Repairs typically cost about $200 per metre.

On the outside, salt can rise into masonry. When it dries, it can lead to salt fretting of bricks. Eroded bricks must be replaced.

Ventilation

Look under the floor of the building if you can. Shine a torch under the floor to look for signs of moisture, mud tunnels due to termite activity, fungal growth .n timber and ponding water.

Check vents. Poor ventilation can lead to continual mould in the home and rotting of timber. Many old homes have poor underfloor access, making repairs expensive and at times nearly impossible.

Mould and condensation

General mould around the upper walls and ceilings is an indication that the house suffers from condensation.

Look in the bathroom and laundry for exhaust fans and make sure they work.

Flueless gas heating can add a litre of water to the inside of the home each hour, leading to condensation.

Check that underfloor ventilation is adequate to void constant high moisture conditions.

A southerly aspect, with overhanging trees, rooms built into the slope and poor ventilation all make a house cool and always humid, with walls which can't dry out.

Drummy tiling and render

Drummy tiling is due to the adhesive bond between tiles and wall or floor breaking down.

Run the plastic handle of your screwdriver over the tiles and listen for a hollow sound.

In modern homes with huge tiled areas, drummy tiles often result from floor tiles being installed without expansion joints. As tiles expand with age, the stresses cause the adhesive to fail. The only repair is to totally retile.

Drummy render can be a dilemma. It could indicate cracking in the walls behind or may simply be due to slight movement and breaking of the bond to the brickwork. It may stay there for many years or fail within the hour. If buying a house with drummy plaster to restore or renovate, count on re-rendering, which is a considerable cost.

Check plumbing

In the bathroom and kitchen, check the flow of water. Turn on a tap, then another, to see if the water flow lessens dramatically. The pipes may be corroded or there may be a restriction. Rusted galvanised pipes will soon need replacing with copper, which can become expensive.

Turn the taps on sharply to see if there is any noise. There may be water hammer, or banging in the pipes, which over time can lead to weakening of soldered joints.