A £24 million regeneration of County Hall in Trowbridge will finish within budget and on time, Wiltshire Council has said, as the first phase nears completion.

Trowbridge Library, currently opposite County Hall, will close at the end of August and a new library with 1,000 sq ft of floor space will be unveiled.

A vast new courtyard at the heart of County Hall, covered by a glass roof, will become a cafe and meeting point for council workers and the public.

Cllr John Thomson, deputy leader of the council, said: “I am pleased to say that it will not only be on time, but it will also be under budget.

“This is one of the biggest investments in Trowbridge in recent years and what we want to do is really open up County Hall to the public as much as possible, so people will be able to come in here and go to the library, then enjoy a coffee or a spot of lunch.

“It will also be a nicer setting for council workers to come down from the office when meeting the public. It will encourage them to mix in a more social and relaxing atmosphere.”

The space will be available for hire for conferences and wedding receptions. A registry desk will be installed in one corner, to make way for the closure of the Trowbridge Register Office.

Phase one will be done by September, then phase two will run until the same time in 2013.

Until now, council meetings have had to be held elsewhere because of a lack of disabled access to the council chamber, but that will be remedied.

Project manager Mark Butt, of Wiltshire Council, said: “We want this to be one of the greenest public buildings in the country. The building will collect rainwater and its design will mean that it will use 40 per cent less energy.

“It is always a fine balance between trying to design a building which incorporates well with the older part of County Hall and being as green as possible.”

It will be an open plan design throughout, with 20,000 sq m of office space, while the glass roof has been likened to that of the Eden Project in Cornwall.