Six in 10 (57%) landlords could be missing out on cheaper green mortgages, Paragon Bank research found.
57% of landlords who had paid for energy efficiency upgrades had not arranged a new energy performance certificate (EPC) assessment after the work.
This means many may not qualify for lower mortgage rates offered to properties with energy EPC ratings of A to C.
28% of landlords did get their properties reassessed after upgrades, which led to an improved EPC rating.
Meanwhile, 14% found no change in their rating.
Separate research from Pegasus Insight for Paragon Bank found that six in 10 landlords own a property with an EPC rating of D.
A quarter have at least one property rated E, F or G.
Just under half of the typical landlord’s portfolio did not meet the proposed standard of EPC C or above, which is being discussed by the Government for the private rented sector (PRS).
Louisa Sedgwick, managing director of mortgages at Paragon Bank, said: “We were one of the first lenders to launch green mortgages, offering lower rates for properties with EPC ratings of A-C, incentivising landlords to purchase homes with better energy efficiency.
“These rates are also available on remortgages so we’d encourage landlords to reassess their properties following any energy focused upgrades because they could be eligible to take advantage of lower pricing.
“This research aligns with Government data highlighting how millions of properties will need to be upgraded to meet the proposed new minimum energy efficiency standards.”
Sedgwick added: “As a result, we believe the 2030 target for all rental properties is unrealistic and could exacerbate the undersupply of homes for tenants.
“We’ve responded to the Improving the energy performance of privately rented homes consultation, calling on Government to abandon its 2030 target and instead adopt a phased implementation between 2030 and 2035.”
