After spotting a water stain, homeowners should consider where the possible source of the stain is, Kuhn says. If there's a bathroom above the water spot, the leak may be a plumbing issue. That could be a costly repair, she says, because a plumber may need access to an interior wall to repair the leaking pipe.
If the water spot appears to be rainwater coming through the roof, it's not necessarily a major expense, especially if the roof is fairly new, Marston says. It could simply be a nail that popped through a shingle on the roof, or flashing (which secures pipes to a roof) that hasn't been caulked properly, he says.
"Those problems are relatively simple to fix," Marston says. "They usually cost a couple hundred dollars for a roofer to repair."
Other problems could be more expensive to fix. For example, if the roof is 15 years old and several shingles have blown off, the roof is probably in poor condition and requires a complete replacement, Marston says.
"Most builder-grade asphalt roofs have a life expectancy of 15 to 20 years," he says.
COST: According to Marston, new roofs cost from $5,000 to $12,000, depending on their size.