Dozens of firefighters spent ten hours tackling the fire at the former Green Oaks school in Kingsthorpe on Saturday.
it's one of several former school sites currently lying empty across Northamptonshire after a change to the education set-up.
The county council had been hoping to sell them all off to a developer in one transaction for new housing. But when the economy crashed interest in the project cooled and the authority's been left to maintain security at the majority of the sites.
On the Saturday, more than 50 firefighters tackled the flames on the Bective Road site and two boys, aged 15 and 16, were arrested on suspicion of arson before being released on bail.
Since then the council has said manned patrols had been introduced at the site, along with new fencing, and it's expected the area will have to be bulldozed. There's no estimate yet on the cost of the extra security measures.
The council has defended its policy of hanging onto the sites with Andrew Langley, from the Property Services Department, telling Heart: "the problem with empty buildings is that no matter how well you try and create security around them if people are intent to cause criminal damage then it's almost impossible to stop them."
In terms of retaining the school sites he added: "the property market is very difficult for us. the market wouldn't be served locally well in our interest if we marketed all of our sites in one go as we would be creating a deluge of supply."
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