Teachers across England have complained of leaking ceilings, broken heating systems and ventilation too poor to deal with the threat of Covid, as the overwhelming majority of headteachers warned that they do not have the funds to repair their dilapidated school buildings.

The Observer has been contacted by teachers who say they have had to empty water out of their keyboards in the morning, move tables and chairs each day to avoid puddles and ask children to wear coats inside in winter as a result of unsuitable buildings in dire need of repair.

A staggering 83% of school leaders said they do not believe they have sufficient capital funding to maintain their buildings and facilities. The finding, from a 1,500-strong survey of leaders conducted by the National Association of Head Teachers (NAHT), comes just months after a government-commissioned study found that the repair bill for state schools in England had ballooned to GBP11bn.

There are now calls for heavy investment in this autumn’s spending review, with heads blaming a decade of austerity. Concerns have been heightened by the new term and an anticipated rise in Covid cases, with teachers worried that faulty windows and air conditioning systems will prevent the ventilation required to lower the risks of the virus spreading.

A spokesperson for the Department for Education said the government has “invested GBP11.3bn since 2015, to enable schools to refurbish their buildings, including GBP1.8bn in 2021-22 alone.” They also cited the “new 10-year school rebuilding programme to transform 500 schools”.

Scores of teachers contacted the Observer to raise concerns about their schools. Their testimony echoes the official survey of school buildings, finally published earlier this year, that found GBP2.5bn was needed for electrical and IT repairs, GBP2bn on “mechanical services” such as air conditioning and boilers, and GBP1.8bn on external walls, windows and doors.

Many other teachers spoke anonymously about conditions in their classrooms. A teacher in South Gloucestershire said she had often tipped rainwater out her keyboard before taking the register because of a leaking ceiling, while temporary cabins were being used that should be replaced. Another from Oxfordshire said the heating in their school had broken down twice in the past four winters, with classrooms at 11C, even with portable heaters. Another in Bedfordshire said some of the windows in her classroom were falling apart so had been bolted shut, leaving only two that opened a small amount.

A primary teacher on Merseyside listed a series of issues at her school. “The roof leaks, so, of a morning, if it’s been raining, you have to move the tables so that the children don’t sit on wet chairs. Children sit in their coats during the winter. Our heating system is antiquated. And they have said that, if it breaks down, there aren’t any parts to fix it. There are small, A4-size windows that don’t provide enough ventilation. How much better would our children do in a clean, warm, well-ventilated, spacious environment?”

A Yorkshire primary teacher compared conditions in his school with his time in the military. “Decaying buildings, poorly maintained accommodation, and generally less-than-pleasant digs are not alien to me,” he said. “My room alone is constantly being taken over by mould. It’s around the window frames, climbing up the walls, and creeping down from the ceiling. This is partly down to the leaking roof.”

A London secondary teacher spoke of rats living in the roof and spotted in the staffroom. Another teacher at a London school said the “appalling condition” of a building meant someone had to stand on a roof and sweep off the rain as it fell to stop leaks.

A teacher in Sunderland said she often shivered while marking homework in the winter, while windows “don’t open in summer (or pandemics) to allow for ventilation: they are metal-framed sash windows which just don’t budge”.

Merche Clark, a governor at St John’s primary school in Bristol, said issues included water ingress, and problems with the roofing and electrical wiring. “A number of teaching spaces are poorly ventilated or have heating issues in the winter months,” she said.

Geoff Barton, general secretary of the Association of School and College Leaders, said investment had “completely failed” to match need for a decade. “The government has recently launched a school rebuilding programme, which we welcome,” he said. “But we are not convinced that this goes far enough in meeting the overall requirements for repairs and refurbishment, and we believe that the government needs to develop a more strategic and sustainable approach to maintaining schools. It is surely not too much to ask that every child is able to learn in buildings that are fit for purpose.”

James Bowen, head of policy at the NAHT, said that the pandemic had “laid bare the scale of the problem”. He said: “Issues like ventilation and having enough space suddenly became really important. We were desperately ill-prepared for that.

“The government’s latest advice on ventilation for schools said open as many windows as you can. If your windows are screwed shut because they’re not deemed to be safe, or you’ve got external doors that are faulty, that’s a real problem.”