Greenroofs will be mandatory on new apartment, commercial, leisure and educational buildings in one of the country's most affluent suburbs.
Any large building with a roof space of more than 300 square metres will have to install the eco-friendly measure. It insulates the building, lowers energy costs, absorbs water, which can reduce the risk of flooding, and encourages wildlife into the city.
The measure, which was agreed by councillors in Dún Laoghaire Rathdown County Council, takes effect from January 1 and will require at least 60pc of the roof space to be covered.
The cost of installation ranged from €45 to €100 per square metre, the council said.
The measure was proposed by People Before Profit councillor Karl Gill, who said it would encourage wildlife into the south Dublin suburb.
"Large buildings will now have to construct their roof space with grass and foliage which will greatly assist in terms of preventing flooding and helping drainage systems," he said.
"If we are to have large-scale development near the bay, it's important that biodiversity is encouraged. It will also help in terms of reducing carbon emissions."
The council also has stringent environmental standards for housing, which require new developments to achieve very high energy standards to reduce heating bills.
Mr Gill said all local authorities should introduce similar policies. Green roofs are common across large parts of North America, and are seen as a low-cost way of reducing heating and cooling bills which help to reduce carbon emissions.
In a report to councillors, local authority management said it was "appropriate" to encourage the development of green roofs as they played an important role in reducing flood risk.
Between 40pc and 70pc less water entered storm drains, as it was absorbed by the vegetation. For 'intensive' green roofs, it could be as much as 90pc.