A passer-by raised the alarm and told the Bradford Telegraph & Argus the fire was “quite intense”.
The brigade had the blaze under control within the hour.
GB has been on site since last January with the job due to finish next month.
The Sustainable Enterprise Centre is one of the greenest buildings in the country and is made from an innovative mix of materials including a gulam engineered timber frame and Lytag recycled aggregates.
It also has walls made of hempcrete – a blend of a lime-based binder and the woody core of the hemp plant.