At least £6.7 billion is needed to restore all school buildings to a satisfactory condition, the government's spending watchdog has warned.
The National Audit Office has today highlighted the "significant challenges" faced by the government over the need to improve school buildings and create more school places.
In a report, Capital Funding for Schools, the NAO also states that the Department for Education has "responded positively" to the challenges, for example by improving schools in the very worst conditions.
However, it states: "The condition of the school estate is expected to worsen as buildings in poor, but not the worst, condition deteriorate further.
"Pupil numbers are continuing to grow and the demand for places is shifting to secondary schools, where places are more complex and costly to provide.
"The department, local authorities and schools will need to meet these challenges at a time when their capacity to deliver capital programmes is under growing pressure as revenue budgets become tighter."
Common problems included faults with electrics, walls, windows and doors, the report says, adding that it would take £6.7 million to restore all schools to at least a "satisfactory" condition, and a further £7.1 billion to take them all to a "good" condition.
Malcolm Trobe, interim general secretary of the Association of School and College Leaders, said: "Schools are having to cut all areas of revenue expenditure, including maintenance budgets, because the level of per-pupil funding is frozen while costs are significantly rising.
"As a result of this funding squeeze, it is increasingly difficult for schools to afford the costs of preventative maintenance and this situation is likely to result in the further deterioration of the school estate.
'Paying a premium'
The report also raises questions about the cost effectiveness of the government's Free Schools programme. The government wants to create 500 free schools by 2020, but there is a shortage of suitable sites – leading to the department paying "large sums" to secure land – the report says.
The average cost of the 175 sites bought for free schools is £4.9 million, but 24 sites have cost more than £10 million each. Twenty sites exceeded their official valuation by more than 60 per cent, "indicating that the department had to pay a premium to secure the land required."
The DfE estimates that 83 per cent of free schools approved since September 2013 have been in areas where school places were needed.
But 57,500 out of 113,500 new places in mainstream free schools opening between 2015 and 2021 will create "spare capacity" in the schools' immediate area, which could affect funding in neighbouring schools, the report says.
Spare places at the 52 free schools due to open in 2015 were felt to have a "moderate or high impact" on the funding of 282 neighbouring schools, according to DfE data.
But local authorities face difficulties in fulfilling their statutory duty to provide enough school places because they do not control the number of places in academies or free schools, the NAO said. In the 30 per cent of cases where the opening of a free school has been delayed, councils may have had to make alternative arrangements to provide the necessary places, the report added.
The report highlighted a trend for bigger classroom sizes, with the proportion of infants in classes of more than 30 pupils stabilising at 6 per cent – three times the percentage in 2008.
Richard Watts, chair of the Local Government Association's Children and Young People Board, said: “If we’re to meet the demand for school places then existing academy schools should expand where required, or councils should be given back the powers to open new maintained schools”.
“No child should be without a place but councils fear that they will no longer be able to meet the rising costs for the creation of spaces, nor find the space for new classes, if they aren’t given the money or powers to do so.
“LGA research shows that councils have already diverted over £1 billion of their own budgets to create more places," he added.
But Toby Young, director of the New Schools Network, said that free schools offered better value for money than previous school building programmes.
He added: "They are the most cost effective way to create the 750,000 new school places we need between now and 2025. They are also more popular with parents and more likely to be rated 'outstanding' by Ofsted than any other type of school."
Despite the challenges raised in the report, the NAO said the DfE "has created a large number of new school places and is making progress in improving schools in the worst condition". The report added: "It has also improved how it manages its capital funding through bettwe use of data and greater targeting of resources at areas of most need."
A Department for Education spokesperson said: “As the NAO acknowledges, we have made more school places available, and in the best schools. The free school programme is a vital part of this – more than three quarters of free schools have been approved in areas where there is already demand for new places and the vast majority of those inspected are rated 'good' or 'outstanding' by Ofsted.
“The government is making a huge investment in the school estate of £23 billion up to 2021, to create a further 600,000 new school places, deliver 500 new free schools, and rebuild and refurbish buildings at over 500 schools.
“But we want to go further. That’s why we have set out plans to create more good school places, in more parts of the country, by scrapping the ban on new grammar schools, as well as harnessing the expertise and resources of our universities, and our independent and faith schools.”