Boris Johnson's decision to extend green homes grants by another year should be stretched to the next two decades, urges the construction industry. Getting existing buildings more energy-efficient is going to take longer than a year warn builders and surveyors.

The Federation of Master Builders, FMB, chief executive Brian Berry said: "Our existing homes contribute 20 per cent of all our carbon emissions and consume 35 per cent of our energy. A long-term retrofit strategy is needed over the next two decades to make all our existing homes more energy-efficient.

"Such a strategy has the potential to create hundreds of thousands of new jobs and save the NHS as much as £2 billion because of the cost of people living in poor housing conditions."

The Royal Institution of Chartered Surveyors, RICS, has said the grants are not enough to help with the costs of home insulation, heat pumps, or solar thermal heating systems. Government vouchers of up to £5,000, and £10,000 for those on benefits, is insufficient, it claims.

"Only a small proportion of properties can be renovated within the scope of current incentives made available by the UK government," said RICS data analyst Jon Querejeta.

Existing building stock with poor energy ratings is massive

More than half of the UK's 29 million houses and more than a third of its one million commercial properties were built before 1970 and as a result, have low energy performance ratings.

"In our opinion focusing on renovations and retrofitting should be central to the green recovery. The green homes grant scheme is a good start and we recommend that the government should consider using the scheme as a pilot project to roll out more energy renovation measures and incentives," said Mr Querejeta.

RICS would like all properties to be brought up to a minimum energy performance certificate rating of C by 2035. New build housing generally has an energy performance rating of at least B, however, it makes up just one to two per cent of current housing stock.

The professional body argues if VAT on repairs and maintenance was cut from 20 to five per cent this would be a motivator for homeowners hiring traders to do energy performance work.

Brokers Hank Zarihs Associates said development and refurbishment finance lenders were keen to support builders in embracing the business opportunities green retrofits presented.