Vinci has been brought in to expand the Derwent Centre, where mental health services (inpatient and clinics) are provided.
The contract covers the second, third and fifth phase of a project to revitalise the centre.
A new outer shell will be created and floor space will be vastly increased by adding three new storeys.
The ground and first floor levels will be refurbished and fitted out. Landscaping will also be carried out in the surrounding area.
Single, en-suite rooms will provide patients with comfortable personal space. The design also includes separate reception areas for new patient admissions and visitors, thus creating a calmer environment and reducing anxiety and stress.
Vinci project manager Andy Knowles said: “We are delighted to be working with the trust on this project. We know patients will see the significant improvements as the single room layout will increase privacy and patient dignity and improve the healthcare outcome.
“The inpatient wards will also be close together giving a more flexible staffing response to patient’s needs.”
North Essex Partnership chief executive Andrew Geldard said: “Since buying the Derwent Centre we are rebuilding it from the inside out. We have already created the garden with easier access and some new therapy spaces. This phase will transform the wards.”
The project is scheduled for completion in November 2015.