Global warming could make naturally ventilated offices virtually unusable for up to one quarter of the year, according to a study by Arup

The report predicts that the temperature inside a 1960s office block could reach 39°C by the year 2080.

The researchers also forecast that the temperature inside this office will be above 28°C – the temperature at which people suffer discomfort – for a quarter of the time it is occupied. The findings mean that developers, designers and housebuilders will need to change the design of buildings if they are to remain in use as climate change takes effect.

Gavin Davies, associate director at Arup Research + Development and one of the report’s authors, said: “The existing building stock has not been developed to deal with future climate change.”

Employers may have to change the way people work in the summer. Arup recommends relaxed dress codes, sending staff home during hot spells, flexible working hours or longer summer holiday, siestas. It also suggests moving firms to the north of England.

Houses will also by vulnerable to the effects of climate change. From 2020, modern homes could overheat – reaching temperatures of 40°C by 2080.

The report suggests air-conditioning and mechanical ventilation may have to be fitted to dwellings to keep them at an acceptable temperature.

The research was carried out as part of a study for the DTI. The study is one of the first to make a quantitative assessment of the risks of climate change to the built environment.

The study used design data produced by the Chartered Institution of Building Services Engineers and modified it to take into account the latest predictions from the UK Climate Impacts Programme for the years 2020, 2050 and 2080. Arup used this data in a thermal modelling programme to predict the temperature in different building types.