IT will cost an extra £400,000 to expand Dunkirk Primary School, Nottingham City Council has revealed.
The school is set to open a new site in September at the former Lenton Primary School buildings in Lenton Abbey to provide more space.
Around £850,000 was set aside to refurbish three buildings on the site but now a council report says another £400,000 is needed for the project.
It states: "As work progressed on site, a number of severe and unforeseen health and safety and condition issues were identified that required additional funding."
The council says there have been problems with the roof as well as other structural issues with the site, and problems with boilers, heating systems and electrical wiring.
The council has said that the extra money has been made available by "achieving savings on other schemes and reallocating unspent funding from the capital programme."
However it has also warned that further funding will be required for the project, which will be subject to another report.
Lenton Primary School only closed in 2008 because of a surplus of primary school places at the time.
However, many parents fought against its closure at the time and have criticised the council for the U-turn now.
The revamp plans would see pupil numbers at the Dunkirk school double and is the latest in a string of ideas to increase primary school capacity.
The council is spending £14.5 million to create more than 1,000 extra spaces across the city.
Councillor David Mellen, portfolio holder for children's services, said: "There is an urgent need to address the acute shortage of school places in Nottingham."
