A doctors' surgery is expected to remain shut for another fortnight as investigations continue to work out the source of air quality issues.
The GP practice at Caister Health Centre has been closed since 6 May after several staff reported symptoms of tiredness and headaches.
Contractors have been called in to assess air quality, including issues thought to emanate from drains or sewers.
Jonathan Knights, executive manager of the East Norfolk Medical Practice which runs the surgery, said he would "like to think we are getting closer to understanding the problem".
On 29 April, paramedics, firefighters, police and gas network engineers were called to the site in West Road after 16 staff said they felt unwell.
The premises reopened the next day, but closed again a week later as staff reported the same issues.
A pharmacy and dental practice also operate in the building.
The Wellbeing Pharmacy ran a restricted service, with customers not allowed inside the shop and instead served at the door. John G Plummer and Associates dental practice reopened last week.
East Norfolk Medical Practice said the building – owned by a private landlord – had not undergone any recent works or alterations.
Mr Knights added: "We had the contractors down on Friday afternoon looking at the sewers and pipes in and around the building and there's a couple of points of interest they want to explore further.
"They are going to come back on Wednesday to do some further investigation.
"What we are aiming to do, depending what happens on Wednesday, is looking at getting reopened by 16 June."