Upper Perkiomen High School in Montgomery County will be closed this week because of moisture and mold issues, the school district's superintendent wrote in a letter to parents on Saturday.

The Pennsburg Borough school will be closed Sept. 10 through 14, while the district's elementary and middle schools will remain open.

Superintendent Alexis McGloin said in the letter that the high school's HVAC system needed significant changes to address the problem. Over summer break, contractors cleaned up some mold, replaced air filters, and brought in dehumidifiers.

But amid persistent hot and humid weather, new problems have popped up, such as mold growth in the gymnasium, McGloin wrote. The district asked contractors to take a deeper look.

"Our system simply can't keep up at this point," the superintendent wrote. "We want to ensure that this problem is addressed properly and we are not looking to cut corners on this important issue, so a building closure is unavoidable."

McGloin said the district had scheduled four make-up days: Nov. 6 (Election Day), Nov. 19 and 20 (which had been scheduled for parent-teacher conferences, to be rescheduled at a later date), and Jan. 21 (Martin Luther King Jr. Day).

An extra day had already been built into the school calendar, so there won't be a fifth make-up day. A school board meeting is scheduled for Thursday at 7 p.m.