Traditional buildings with fewer windows than modern glass and steel structures are more eco-friendly, according to a recent study.

The study, commissioned by Robert Adam Architects, found traditional buildings with solid walls cost 15-20% less to heat and cool than modern designs with lots of glazing, UK newspaper The Telegraph reports.

Even when the glass facades of modern buildings faced north or south, gains made from extra daylight were offset because occupants tended to close the binds on bright days and put the lights on.

Robert Adam, the architect who commissioned the study, says the results would not surprise the architectural community.

“Actually the architectural establishment do know this but they don’t want it said – that traditional buildings are more sustainable. Environmental engineers know this too but they tend to work for architects,” he says.

“This is a great secret that no one wants to reveal,” he added.

“Glass and steel is a default position for the architectural profession, but it is fundamentally unsustainable.”