Extra examination rooms are being built at Kingsmill Hospital in Sutton In Ashfield after a sharp rise in patient admissions.
Numbers have risen by two-thirds over the past few months, to as many as 250 a day.
Building work is now underway to ease the cramped conditions with improvements to the casualty department due to be completed by December.
It is hoped the works will mean more examination rooms and less waiting around in corridors for patients.
Janet Noon, Department Leader: "We believe the increase is due to the hot weather.
"A high level of pollution in the air is also affecting patients with chest complaints like asthma.
"While the sunshine also means a lot of people have been doing DIY or work in the garden."
The changes are being welcomed by patients and their families.
Melanie Normanton, who had taken her son Toby to the accident and emergency department after an accident at school, said: "I definitely think more space is needed when you first walk into the department.
"They should concentrate on more waiting room space because it is a bit overwhelming when you first come in and see all the people with their different injuries."