A SHARED education campus in Co Tyrone will cost almost £60 million more than first estimated.
The Strule campus in Omagh will involve six schools and is due to be complete by 2020.
A mix of grammar, non-grammar, Catholic, state and special schools will occupy the site.
Each will have their own buildings but will share other facilities in an attempt to increase opportunities for collaboration.
So far, just one school has opened - Arvalee School and Resource Centre - which was built at a cost of £8.2m.
It has now emerged that converting the former Lisanelly military barracks will cost almost £60m more than first thought.
Initial projections, provided at the very early stages of planning, estimated that the bill would be about £100m.
Responding to questions at the assembly education committee in June this year, Department of Education officials said the cost would be closer to £140m.
Just six months later, the department has said the latest estimate is £159m.
The Executive's commitment to Strule will have a major impact on money available for other building projects.
It is understood that one third of all capital funds every year will be tied up in the Omagh scheme, with schools across the north competing for the limited remaining cash.
Up until now, money for the Strule project has come from the Executive's Together: Building a United Community (T:BUC) strategy. Now, funds must come from the Department of Education.
Officials confirmed that there will be a significant impact in both 2018/19 and 2019/20.
The department was asked by the Irish News to give an up-to-date estimated cost and timeframe for the construction of the five other schools.
"At August 2016 prices the latest estimated total construction cost of the Strule Shared Education Campus, including expenditure incurred before 2016/17, is £159m," a spokeswoman said.
"This includes the construction of the six core schools (including Arvalee School and Resource Centre which opened on 6th September 2016), shared facilities, site works, road works and professional fees. Optimism bias is included. This estimate excludes other non-construction programme costs."
All old military camp buildings and structures, she added, had been removed as part of a demolition contract which completed earlier this year.
"The site preparation works contract scheduled to start in early 2017 involves the re-alignment of services, roads and earthworks within the site to make it ready for construction of future facilities in autumn of 2017," she said.
