1. The house has poor drainage.
This is the most common problem found by home inspectors. To improve drainage, you may have to install a new system of roof gutters and downspouts or have the lot re-graded to better channel water away from the house.

2. The house has faulty wiring.
An insufficient or out-of-date electrical system is a common problem, especially in older homes. This is a potentially hazardous defect and not to be taken lightly. You may have to replace the entire electrical system, or at least part of it, to bring this home up to code or to make it safe.

3. The roof leaks.
If the roof has water damage, it may be caused by old or damaged shingles, or improper flashing. It's cheap and relatively easy to repair shingles and small amounts of flashing, but if the roof is old, you face a much larger expense to replace the whole thing.

4. The house has an unsafe heating system.
An older heating system or one that has been poorly maintained can be a serious health and safety hazard. You may have to repair or replace the old furnace. This is a major expense, but new furnaces are more energy-efficient, which will probably save you money down the line. If your heating system is anything but electrical, install carbon monoxide detectors in a couple of locations in the house.

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5. The whole house has been poorly maintained.
Examples of poor maintenance include cracked or peeling paint, crumbling masonry, broken fixtures or shoddy wiring or plumbing. You can easily repaint a wall, replace a fixture or repair a brick wall, but makeshift electrical or plumbing situations are serious and potentially dangerous problems. Replace any such wires or pipes.

6. The house has minor structural damage.
Minor structural damage means the house is not likely to fall down, but you should deal with the problem before it becomes more serious. Such damage is usually caused by water seepage into the foundation, floor joists, rafters or window and door headers. First you need to fix the cause of the problem (a leaky roof, for example), then repair or replace any damaged pieces. The more extensive the damage, the more expensive it will be to repair.

7. The house has plumbing problems.
The most common plumbing defects include old or incompatible piping materials and faulty fixtures or waste lines. These may require simple repairs, such as replacing a fixture, or more expensive measures, such as replacing the plumbing itself.

8.  The house's exterior lets in water and air around windows and doors.
This usually does not indicate a structural problem, rather poor caulking and weather stripping that require relatively simple and inexpensive repairs around windows and doors.

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9. The house is inadequately ventilated.
Poor ventilation can result in too much moisture that wreaks havoc on interior walls and structural elements. It can also exacerbate allergic reactions. Install ventilation fans in every bathroom if there are no windows, and regularly open all the windows in your home. To repair damage caused by poor ventilation, you may only have to replace drywall and other inexpensive pieces. If you have to replace a structural element, it will be more expensive.

10. The house has an environmental hazard.
Environmental problems are a new and growing area of home defects. They include lead-based paint (common in homes built before 1978), asbestos, formaldehyde, contaminated drinking water, radon and leaking underground oil tanks. You usually need to arrange a special inspection to determine environmental problems, and they're usually expensive to fix. For example, it costs $1,000 to install a radon-ventilation system, and about $6,000 to remove a leaking oil tank.