Authorities received a call just after 1:00 p.m. Thursday about an unconscious male on the roof at the school in the 900 block of Meetinghouse Road in Upper Chichester.
When they arrived they found four people needing medical assistance.
One worker passed out on the roof and firefighters rescued him. Another worker fainted after climbing down the ladder to the ground on his own.
Three of the workers were treated at Corzer-Chester Medical Center. The fourth refused treatment at the scene.
"Working hot tar, it's probably about 130° on that roof," said Boothwyn Assistant Fire Chief Sandy Monetllo. "Combined with using 420° tar itself."
Other contsruction workers handling projects at the middle school told Action News the conditions were tough for them.
"The human body can only take so much," said construction worker Bruce Rambert. "You get dehydrated -- that's it."
"You got to deal with it, you know. Or you don't make no money," added Ronald Balencajeo.
Another roofer who was packing up for the day said that the four workers who were overcome by the heat were new to the job. He added that the team wanted to start their jobs earlier in the day around 5 a.m. but they couldn't because of neighbors' complaints about the noise.