There are many surprises that can affect the timeline and cost of a remodeling project.

The wall you planned to remove, for example, is housing the main plumbing stack. Remove the wall and you face an expensive rerouting of the plumbing. Leave the wall intact and you lose the ability to create a large, open kitchen and family room.

While it is impossible to predict all potential surprises, there are some common ones to consider before you start. In some cases, planning ahead can help make the added costs and change in timing more manageable.

Structural Surprises

Structural surprises can be the most costly and have the biggest impact on the schedule. The contractor may open a wall and find that the studs were not installed properly, there is damage from termites or the wiring has to be updated.

The best way to prepare for structural surprises is to hire a qualified contractor and, in some cases, an architect, who have experience with the type of project you are undertaking. Ask them what type of surprises are common with this type of project. How can they affect your timeline and budget?

If you are adding a room, for example, look for someone who specializes in room additions. That person will be able to survey the lot to look for potential problems with the topography or the drainage.

Among the common structural problems are:

• Inadequate or unsafe wiring and plumbing
• Deteriorating foundation walls, particularly in older houses
• Settling issues -- sloping floors, uneven doorframes, etc.
• Framing or support problems, such as walls that cannot support cabinetry

By planning ahead for problems, you can reduce delays in scheduling. Because construction occurs in stages, one surprise often creates a snowball effect. If a problem is found during the excavation, it will delay the carpenters who will frame the addition, then the plumbers.  In some cases, those workers move onto other jobs, forcing you to wait until they can come back to finish yours.

What Your Contractor Should Know

When you are hiring a contractor, also look for someone who has worked in your neighborhood or municipality. He or she is more likely to be familiar with soil and grading conditions, local zoning ordinances, and the lead time needed for city inspections.

Talk with the contractor early in the process about how any surprises will be handled. Make sure that any contract you sign gives you the right to make decisions regarding changes to the project. If specialists have to be called in, you want to have final approval before they are hired.

The Extra Costs

Surprises often lead to more expenses. It is wise to set aside 10 to 20 percent of your total project costs as a contingency fund. Otherwise, you might have to sacrifice the fancy wall tile in order to pay the electrician's bill.

Another way to protect your budget is to ask the contractor to specify a rate of pay for work that is outside of the scope of the project. "You can't leave this guy a blank check," said Rick Baumgarten, president of Lee Lumber & Building Materials in Chicago.

"If the contractor says he didn't know he was going to move the light switch and it will be $850, then you're in trouble," Baumgarten said. "If it takes an hour and he quoted you $58.50 an hour, then it's $58.50."

Scheduling Issues

Aside from structural problems, you may encounter surprises related to the contractor's business practices. If he is juggling too many jobs or having difficulty finding qualified subcontractors, the project will be delayed.

Establish frequent check points during the project to ensure the work is on schedule. If you notice that workers are not on the job site for several days, ask for an explanation. It could be a normal break in the schedule or a sign of problems with the workers.

Other surprises might arise when the municipality inspects the site for code compliance. A contractor who is unfamiliar with the local zoning laws or tries to cut corners with the construction can drastically impact your schedule and cost. An inspector can force the contractor to stop work on the project or to remove the new plumbing wall and start over.

While surprises are a natural part of the remodeling process, it helps to anticipate issues that can slow down the progress or add to the cost. When surprises occur, you will be more prepared to examine your options and make a decision about moving ahead.