ERWOOD Bridge will close for a year for refurbishment works costing nearly £1million.
The bridge, six miles south of Builth Wells, needs strengthening and will close to all traffic from July 25 but will remain open to pedestrians.
Traffic will be diverted Llanelwedd via the A481, or to Builth Wells via the A438.
South Wales company Dawnus Construction has already started preliminary work but this will not restrict traffic.
The project, costing £960, 000, is anticipated to re-open by June 2014.
There will be a drop-in session at Erwood Village Hall on July 8 from 4-7pm where residents can view the proposed work and ask any questions they have about traffic management plans.
"We understand that these planned works to Erwood Bridge will cause disruption to the local community,” said Powys council’s cabinet member for highways, Barry Thomas.
“But without these essential works, it may be necessary to apply a weight limit on the bridge or, in the future, close the bridge altogether."