The Welsh assembly's new home has won a leading award for following "green" principles on everything from its construction methods to its toilets.
The £60m Cardiff Bay building, which will be officially opened in March, has been honoured by the Building Research Establishment (BRE).
It has won the BRE's highest award for sustainable construction.
Finance Minister Sue Essex said it was recognised as "at the cutting edge of sustainable design and construction".
"Buildings can be designed to achieve long-term savings in running costs and emissions"
Since the idea was first put forward it has frequently been the subject of controversy, particularly surrounding its designers and cost.
The BRE used its environmental assessment method to give the building its highest rating of excellent.
According to the Welsh Assembly Government, it is the highest score awarded to a development in Wales, and BRE director David Crowhurst said: "An excellent rating is not easy to achieve."
Ms Essex said the assembly government wanted to show developers that "buildings can be designed to achieve long-term savings in running costs and emissions."
The building is designed by the Richard Rogers Partnership, the BDSP Partnership and Arup, and constructed by Taylor Woodrow Construction.
The assessment takes into account such aspects as transport, noise and the use of sustainable materials.
It is said that its renewable energy systems will reduce running costs by up to half.
Other features include using the ground as a heat source and the use of wood chips or pellets for the boiler - although an extra gas boiler is also installed for emergencies.
Rainwater is also collected via the steel columns supporting the roof to supply the toilets and to wash the windows.
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