The Government has set a target of seven million whole-house makeovers by 2020, which would consist of upgrading the basic insulation of a home and then adding other measures such as water efficiency measures, advanced insulation or micro-generation.
The Trust estimates that 6 million homes still need cavity wall insulation and half of all UK houses need more loft insulation.
These measures would save nearly 7 million tonnes of carbon dioxide a year, the organisation said.
The statistics have been released as the Energy Saving Trust prepares to launch its new Sustainable Refurbishment guide, which aims to assist the housing industry in taking a whole-house approach to upgrading the energy performance of existing homes.
The guide, it said, will show how to achieve an ambitious 80% reduction in carbon emissions from a range of different homes through applying home improvements that beyond those required in current Building Regulations.
Said EST chief executive Philip Sellwood: "With the Government's 2016 zero-carbon homes policy we have a clear trajectory to achieving very low-carbon new homes in England.
"We need a similar roadmap towards a low-carbon existing housing stock, setting out a set of standards we expect our homes to reach.
"An existing homes road map will give an incentive for homeowners to invest in home improvements and a clear signal to builders and installers to train staff to be able to deliver the energy and carbon saving measures."