The Scottish Government’s climate change advisers have written to Patrick Harvie calling on him to reform “not fit for purpose” home energy standards.

The appeal comes as the Greens co-leader and the Scottish Government's zero carbon buildings minister ramps up his government’s strategy to improve energy efficiency of homes.

The Scottish Government has pledged for all homes to meet EPC band C energy efficiency standards by 2032.

Gas central heating that produces carbon emissions is set to be banned from new homes in Scotland by 2025 – but work will need to be carried out to upgrade existing properties.

Read more: All homes in Scotland to meet energy standards from 2025 despite £33bn costs

But the plans to end the climate impact of heating homes in Scotland will cost an estimated £33bn, with no delivery plan for the funding yet to be set out.

Nicola Sturgeon previously told The Herald that she was been speaking to financial firms in the City of London over their “willingness and desire” to help fund the key policy – with a reliance on private sector expected to be crucial.

Ahead of the Scottish Government’s campaign being scaled up, Lord Deben, the chairman of the Climate Change Committee (CCC), has written to Mr Harvie, warning that it is “essential” that energy efficiency ratings are appropriate.

In his letter, Lord Deben has stressed that EPCs “are a critically important policy tool for delivery net zero homes”, but warns “the present arrangements are not fit for purpose”.

He adds that despite the purpose being to reduce household climate emissions, “the current rating metrics are poorly suited to this role”, as Lord Deben pointed to “incentivising changes to homes that reduce emissions”.

He said: “Our recommendations to improve EPC rating metrics EPC ratings should provide clear information to consumers about energy use in homes.

Read more: Patrick Harvie doesn't yet know how much of £33bn homes retrofit bill will come from private funds

“The metrics should incentivise homeowners to make their properties more energy efficient and adopt low-carbon heating. They should be designed to support policy mechanisms aiming to deliver zero-emission homes.

“The rating scales should use real-world units so they can be easily understood and compared against actual performance. The ratings should continue to be split into bands to allow simple comparisons between properties.”

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The CCC has recommended four metrics including the “headline” energy metric which would provide people “with clear information about the overall energy use of a home”.

A cost metric would “give a clearer indication of energy costs for a home”.

Lord Deben added: “EPCs could be expanded into an instrument for providing homeowners with advice on risks such as overheating, flooding and water scarcity, and ways to reduce these risks.

“It is essential that the Scottish Government takes this opportunity to get EPCs right, and we hope that our advice can be of help in this regard.”

Mr Harvie said: “Scotland’s homes and buildings currently account for around a fifth of all our emissions, and we are committed to taking bold, ambitious steps to ensure we reduce these to meet our climate obligations.

“The Climate Change Committee is quite right that EPCs need reformed to deliver our climate targets. This is why our heat in buildings strategy set out our commitment to develop a reformed ratings system which gives a stronger focus on both energy efficiency and zero emissions heating, whilst continuing to provide home occupiers with information on current and potential energy costs.  

“We consulted on proposals for a new metric of energy efficiency, based on the amount of energy used by a dwelling, in 2021. This metric would sit alongside the existing metrics on cost of energy and on emissions, providing home occupiers with additional information on how to improve the energy performance and reduce the emissions of their building. 

“We will set out updated EPC reform policy proposals in a further detailed consultation planned this year, including the addition of a new EPC metric based on fabric efficiency that is currently under development with BRE. In parallel, we will continue to work with the UK Government to ensure the UK-wide methodology used to calculate EPC ratings is appropriate for Scotland. We will also consider this latest advice from the Climate Change Committee and continue to engage with them as we develop our policy proposals to reform EPCs.”