GRANVILLE COUNTY, N.C. -- Students at Butner-Stem and Creedmoor Elementary Schools will have to wait a bit longer for their first day of school due to mold.

The two schools have an almost identical footprint. They're both old buildings with outdated HVAC systems.

The issue started less than two weeks ago when Granville County school officials detected mold at Creedmoor Elementary.

“We immediately had some laboratory testing company come in to do testing at the school and we hired a contracting company to clean that school,” said Stan Winborne with Granville County Schools.

Officials started testing other schools and that's when they noticed mold at Butner-Stem Elementary Sunday afternoon. They're blaming the issue on the outdated HVAC system.

“The mold is a result of high level humidity in the building,” said Winborne. “These are older buildings and these HVAC systems are not designed to remove humidity.”

Creedmoor Elementary will open its doors to students on Thursday but doors at Butner-Stem will remain closed until the mold is removed.

While school officials notified Creedmoor parents last week, parents at Butner-Stem didn’t find out about the closure until Sunday night.

“We didn't know until Sunday,” said Winborne. “When we heard there was a potential issue here Sunday morning, then we sent the lab testers to the school to have it tested immediately.”

Crews are testing and monitoring for mold at other schools.

“We don't have any reports to indicate that we need to get out to other schools right now but we're going to follow up and check everything,” said Winborne.

They do plan to replace the HVAC system.

“Cleaning the schools is not fixing the problem,” said Winborne. “The problem is the humidity and that problem is addressed with the replacing of the HVAC system.”

Officials say the estimated cost at Creedmoor is $400,000. They're waiting to see what the cost will be at Butner-Stem.