Partnerships for Schools Chief executive Tim Byles maintained that institutions such as Norwich Union were still coming forward to finance schemes, regarding the investment as "stable and secure".
But he admitted such institutions were now only willing to cough up around£20-£30m, rather than the full amount, meaning a consortia of banks would be needed for each project.
The BSF's procurement methods have been criticised by the head of the architects' body RIBA.
President Sunand Prasad has called for more design competitions and stricter criteria for sustainable design.
RIBA argues that 2016 zero-carbon targets should remain but that both the Partnerships for Schools and ministers need to be less prescriptive about how to achieve those reductions.
Both were speaking at the Children, Schools and Families select committee, Mr Prasad said the current process - which can cost up to£5m per bid - stopped young and innovative practices getting involved in school design.
"We want to see a new Smart BSF introduced which builds on our previous SmartPFI proposals - or the trial of alternative procurement models," he said. "This could fund improvements in design quality."
Ian Fordham, deputy chief executive of the British Council for School Environments, called for more research into existing BSF schools.
"We must do much more to gather the evidence of what works and what doesn't," he said. "We need a rigorous programme of research and development, funded by government."