An Oireachtas committee has heard that there is a danger that we end up "retrofitting the retrofit in ten years' time" due to poor standards.

The Joint Committee on Environment and Climate Action is assessing the impact of the new national retrofitting plan for homeowners.

Oliver Kinnane, lecturer at UCD's School of Environmental Policy, warned that some "A-rated homes are performing at C-levels" following retrofitting.

Some of this is because people are enjoying the comfort of living in a warmer home "because they can" and so are using more energy.

But he also outlined serious concerns around both the quality of work and materials used, which has been uncovered in research.

Around half the fabrics being used in retrofitting "are not meeting designing values", Mr Kinnane said, adding that he was surprised by this finding.

"We also see mis-sizing of heat pumps, poor installation, lack of insulation of piping, long pipe-runs," he said.

As a result, pumps are delivering about two thirds, or even closer to half, the level performance claimed by manufacturers.

Pat Barry, CEO of the Irish Green Building Council, added that some pumps use refrigerants with "very high global warming potential".

They have "600 times" the global warming potential of more carbon-efficient pumps, he said, but emphasised that this issue "could be addressed quite quickly" by the Sustainable Energy Authority of Ireland.

Mr Barry noted that the construction sector in Ireland accounts for well over a third of carbon emissions.

A significant amount of this lies in "embodied carbons", he said, something that is calculated in a "whole-life carbon" approach to emissions, but is not currently included in carbon budgets.

Embodied carbons are caused by sourcing raw materials, processing those materials into construction products and then transporting them, and ultimately disposing of them at the end of their lifespan.

Failing to include them in current carbon budgets "is a major gap in carbon policy", Mr Barry said.

"There is a risk we blow the carbon budget if we do not address embodied carbon emissions," he warned.

He called on the Government to introduce a timeline for their inclusion in construction carbon budgets.

A representative of the European Commission commended some countries who are already moving ahead on this issue.

"I strongly want you to consider this in your work," Josefina Lindblom, Senior Policy Officer on the Environment, told the committee.

She said that such a requirement is included in a directive which is currently being re-negotiated.

Mr Kinnane also pointed to "limiting" restrictions on timber construction in Ireland, in which regard we are "really lagging behind" Britain.

He told Fine Gael's Richard Bruton that while there has been a "good uptake" on people growing hemp for use in construction, "there is no national processing facility here".

Social Democrats TD Jennifer Whitmore said the testimony had been "really worrying" as it highlighted "a blind spot for us" around embodied carbons.

Mr Kinnane said that the construction of 400,000 homes under Housing for All will generate between "4 and 6 megatonnes of CO2 equivalent".

But a shift to using timber materials rather than masonry "could reduce that bill quite considerably", he added.

"It is a lot of construction and it will come with a high embodied-carbon bill," he said