Roscommon and Leitrim have the highest proportion of G ratings, which is the worst awarded.
Kildare has the highest number of homes with the best energy rating, followed by county Dublin and Meath, according to the CSO.
Some 20% of homes in Kildare which have been tested for a BER rating were given an A standard, while Meath and county Dublin have 19% and for Wicklow it's 15%.
The Building Energy Rating calculates a house's efficiency, Roscommon and Leitrim have the highest proportion of G ratings, which is the worst awarded, both counties have 12% G rated - followed by Tipperary on 11, and Mayo and Westmeath with 10%.
Longford and Leitrim have the fewest BER ratings, while Dublin's postal districts have the most with 229 thousand.
C2 and C3 are the most common ratings nationally at 12%.
In total over 1 million BER ratings have been given out since 2009.
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