Wrexham's repair backlog currently stands at pound;27 million and it is also struggling with surplus capacity of more than a fifth in the primary sector.
A recent review by the authority itself acknowledged that the two issues were linked, and Estyn says it now needs better data on school capacity and conditions to make improvements.
In a recent inspection, Wrexham local education authority was criticised for its "unreliable" medium and long-term projections of pupil numbers and told to set "clear interim milestones" to reduce surplus places.
According to information from the Assembly government for 2004, 20.1 per cent of primary school places are surplus - up from 13.3 per cent in 2002, and "too high" according to inspectors.
In 2004-5, around two in five of Wrexham's primary schools had more than a quarter of their places empty, including almost two-thirds of small primary schools.
The authority is now reorganising education through a programme of proposed closures and amalgamations.
Wrexham has made good progress in reducing surplus capacity in the secondary sector from 13.8 per cent in 2002 to 8.7 per cent in 2004, but a significant number of empty places remain in three of its secondary schools.
Access to education was judged as "fair" overall, with "promising"
prospects for improvement. The authority was praised for placing education as its "highest corporate priority". But despite investment of around pound;44m since 1996, Estyn said the condition of many of Wrexham's buildings remain "unsatisfactory", with a maintenance backlog of pound;27m.
While the authority's corporate asset management plan identifies school buildings as a major priority, it does not show what resources are available to fund key elements for improvements, says Estyn.
The inspection agency described as a "significant shortcoming" that heads were also not aware of the criteria for deciding which projects are to proceed and where their school stands in relation to others.
In other parts of the report the authority was praised for efficient management of admissions to schools, and the high priority given to pupils with special needs and those looked after. Its good relationship with schools was also singled out.
Goronwy Morris, senior manager for policy, planning, resource and support, said: "The report recognises the strong commitment of officers and members with key responsibilities, and schools' respect for and confidence in senior officers.
"The authority recognises the high proportion of surplus places in primary schools and the significant backlog of repair and maintenance work outstanding. The first phase of the primary review is due in September 2007, which will inform priorities for investment."