Southern Gas Network will be working for 13 weeks at the roundabout where Fratton Road, Fawcett Road, Victoria Road North and Goldsmith Avenue meet.
Starting on Monday, June 4, both the northbound and southbound lanes of Fratton Bridge will be closed for three weeks each, followed by roadworks on Fawcett Road, lasting five weeks.
SGN is spending £729,000 to upgrade the gas network in Fratton.
The gas pressure regulator will be upgraded and another will be installed the Fratton Bridge roundabout - where Fratton Road, Fawcett Road, Victoria Road North and Goldsmith Avenue meet.
The company says the upgrade will help meet the increased gas demand from homes and businesses. The regulator is a piece of equipment that maintains the pressure in the gas network, so the work aims to ensure a reliable gas supply.
On Fratton Bridge, the northbound lane will be closed for the first three weeks, followed by the southbound route.
A diversion will be in place for drivers during those weeks.
Work starts on Fawcett Road on Monday, July 23 and will last for five weeks.
In Fawcett Road, part of the road will be fenced off and a temporary footpath will be put in.
SGN engineering manager Simon Thurlow said: ‘We’ve worked closely with the local authority in planning this work and we will be doing everything we can to limit disruption during our essential project.
‘We appreciate that roadworks can be frustrating, however, the upgrade to our network will provide more capacity to help meet an increased gas demand in the area.
‘This means that when the work is complete, Portsmouth residents will continue to enjoy the benefits of a safe and reliable gas supply for years to come.’