There was a record number of energy rating certificates issued last year with 105,539 dwellings getting a Building Energy Rating (BER) audit, latest CSO figures show.
This brought the total number of BER audits up to 544,621 conducted between January 2009 and December 2014.
The energy audits show that considerable changes have occurred in the characteristics of recently built housing stock and that the type and age of dwelling are the key determinants of energy efficiency.
A BER rating of C or better was given to just 21% of buildings constructed prior to 1977. Conversely only 23% of buildings constructed since 2000 have received a BER rating of D or worse.
Nearly half (49pc) of detached houses received a BER rating of C or better. This compares with 64% of mid-floor apartments but only 41% of ground-floor apartments and 39% of top-floor apartments receiving a C or better rating.
The figures show that 29% of audited dwellings in Meath and Louth and 32pc of audited dwellings in Cork county had a rating of C1 or better compared with a national average of 23%.
In Dublin 6, Dublin 7 and Dublin 12 over 70% of audited dwellings had a rating of D or worse compared with 55pc for all Dublin postal districts combined. Conversely in Dublin 15, Dublin 17 and Dublin 18 over 61% of dwellings had a rating of C or better compared with 46% for all districts.