He said retrofitting buildings, including schools and local authority housing, would ultimately be self-financing in energy savings.
Mr Devoy also voiced concern about the plight of 2,800 redundant apprentices.
He said they were trapped in the system, as they are unable to complete their apprenticeships, but said they could at least seek jobs abroad if they could complete their training.
The general secretary acknowledged progress in reducing the number of apprentices in this position from 10,000 two years ago.
However, he said the hidden tragedy remained that thousands of young school leavers are denied access to training and potential careers because opportunities in traditional crafts had been largely closed off.