Work to transform a dated office block into affordable flats with a rooftop garden in a Carmarthenshire town could get under way in weeks.

There’ll be 27 flats at the new-look Crown Buildings in Llanelli in a project expected to last around 15 months.

Key to the scheme is greenery on the roof and elsewhere on the five-storey building and low-carbon energy systems including solar panels. The exterior will also be modernised.

The company behind it, Hacer Developments, is completing a larger scheme in Swansea’s Oxford Street consisting of a 12-storey tower, 50 flats, a four-storey greenhouse, rooftop gardens, commercial and education space, and a landscaped courtyard. Part of it is replacing the former Woolworths store.

Carwyn Davies, Hacer Developments’ managing director, said this “biophilic” – roughly translating as people’s drive to connect with nature – design was a key element for the Llanelli and Swansea projects.

“This one in Llanelli will be our first spin-off project,” he said. “I think it’s got great regeneration and community potential. We’re quite excited to roll out the concept.”

Mr Davies said reusing rather than knocking down buildings boosted a development’s environmental credentials because existing materials like concrete, which takes a lot of energy to make, were retained. “We’ve got to start thinking about that,” he said.

Crown Buildings used to be a Department for Work and Pensions office. “It’s well-built with a concrete frame – why would you want to destroy that?” said Mr Davies.

A smaller empty adjacent building will, however, be demolished and a car park created.

Mr Davies said a binding agreement called a Section 106 agreement between Hacer Developmnents and Carmarthenshire Council, which has given planning permission with conditions, has been finalised.

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“We are hoping to start work in the next one to two months,” he said. “A new market is planned in the town centre and the council has done up the [former] YMCA building. We’re probably the first private sector people coming in.”