Here's a home improvement project nobody looks forward to: replacing a sewer line.

For homeowners, the mortgage, property taxes and insurance only account for a portion of the cost of owning an abode.

It's those surprise emergency repairs that can destroy your budget.

Indeed, 18% of homeowners polled by HomeServe USA said that they had no money set aside for surprise repairs. The company, a provider of home repair plans, conducted an online poll of 1,429 homeowners from Feb. 27 to March 1.

More than half of participants said they had a home repair emergency in the last 12 months.

"Part of that can be attributed to the fact that the median age of a home is about 40 years, so that's telling us that homes are aging," said Myles Meehan, vice president of corporate communication at HomeServe USA.

"People should be concerned about maintenance and being prepared for things to break down," he said.