More than half of the United States’ public schools need to update or replace multiple systems or features in more than half their buildings, and failure to address them could pose health and safety problems for everyone inside, according to a government report released Thursday.

What’s more, many district don’t even know exactly what they need: The report says that 65 percent of districts had conducted a facilities condition assessment of their schools at least once in the past decade, and 35 percent didn’t know if one had been done. Only 15 states reported requiring school districts to conduct facilities assessments.

The report comes in the middle of the covid-19 pandemic, during which most schools were closed this spring to stem the spread of the disease. Districts across the country are devising plans to reopen schools, with new protective measures including social distancing and requiring the wearing of masks.

But even before the pandemic, districts struggled to maintain their school buildings, with some of them having to close because of heating or other issues, and others allowing school operations to continue even under unhealthy conditions. (See pictures below.)

The report — released by the Government Accountability Office (GAO), its first study of school infrastructure since 1996 — said that heating, ventilation and air conditioning (HVAC) systems were the ones most in need of repair. Four in 10 districts are estimated to need to update or replace these systems in at least half of their school buildings, affecting 36,000 school buildings nationwide.

That raises issues for schools planning to reopen buildings this fall during the covid-19 crisis. The Centers for Disease Control and Prevention says in its guidelines for reopening schools that ventilation systems should work properly.

Officials in several school districts visited by GAO investigators reported schools have been closed because of facilities problems, and the potential for mold and air quality issues could cause health problems.

“In the last year, several school districts across the country have temporarily closed schools due to hazardous conditions of the school buildings that can pose health and safety risks to students, teachers, and staff,” the report said. “For example, water damage caused by a leaking roof or [HVAC] system can lead to problems with indoor air quality and exposure to substances such as mold or asbestos.”

It said in one Michigan district, officials said about 60 percent of their schools do not have air conditioning.

“In 2019, some temporarily adjusted schedules due to extreme heat,” the report said.

Without air conditioning, schools relied on open windows and fans, which were not always effective at cooling buildings to safe temperatures for students and staff, according to district officials.

“Officials in a Maryland district said the district retrofitted some schools with air conditioning, but did not update pipes and insulation serving the HVAC systems, which has caused moisture and condensation problems in these buildings,” the report said. “Officials were concerned the moisture and condensation could lead to air quality and mold problems, but said to remedy these issues could cost over $1 million for each building.”

The report also found a consistent theme in U.S. education in terms of funding: Students who live in poverty go to schools where less is spent on each child compared with low-poverty schools. In the 2015-2016 school year, it said, of the $44.6 billion spent on capital construction by districts, about $300 less per student was spent in high-poverty districts as compared with low-poverty districts.

Last year, the House Committee on Education and the Workforce advanced legislation authorizing billions of dollars in grants and bonds to help fix school buildings. But that has not been made law, and the covid-19 relief packages from Congress have not directly addressed school infrastructure. In fact, legislation passed in mid-May in the House but not the Senate included $100 billion in direct education funding for K-12 schools and institutions of higher education, but the money could not be spent on capital projects.

Here are some charts and pictures from the report, which you can see in full below:

Here’s the full report: