As a Building Services Engineer, Sara's job is making sure new buildings are comfortable for people to live, or work in. It doesn't matter how amazing a building looks, it's no good if people are roasted inside.

To keep everyone happy she has to consider a variety of factors: how many people will be in the building at any one time; how much sunlight will shine on each part of the building at any time of the year; how much heat will be lost through the walls; how much energy will the systems use.

The Greater London Authority Building, now called City Hall, is an example of Sara's work. Looking like a giant glass egg standing 10 storeys high with 650 panels round the outside it's a fantastic feat of engineering on the banks of the Thames - but all that glass kept Sara's brain busy.

To work out how to keep the building cool in the height of Summer, Sara had to calculate how hot the building is likely to be. She uses data from the Met. Office recorded over the last ten years to work out the average amount of heat that will radiate from the sun. Add to this the heat generated by people and computers in the building, subtract heat lost through the walls and Sara has her answer.

But Sara doesn't just do this once - if the building is to be comfortable all year round she has to repeat the process for every day in the year. Finally, having found all the hot spots and cold corners, all that remains is to work out how to efficiently keep the building comfortable - usually by careful placement of ventilation ducting but sometimes with more unusual systems - such as the external blinds, or louvres seen on the Hemel Hempstead site in the programme.

This is a very involved process, requiring precise analysis and complex calculations yet Sara's job demands more than physics and maths. She has to combine science with an artistic sensitivity to the designer's vision, working within the constraints of the overall design. She says it's perfect for people like her who enjoy, and studied, both science and art.