The lender has also launched 2.5-year fixed-rate new build deals of 2.39% at 85% loan to value (LTV), and 2.59% at 90% LTV.
At the same time, a dedicated phoneline for new build home borrowers and their mortgage brokers is to be rolled out, as part of plans to improve service.
Mortgage extensions will be available across all lending but are expected to be of particular benefit to new build buyers where completions can be delayed by hold-ups in construction.
However, buyers stuck in property chains could also find the change helpful.
Leeds said the extensions could save borrowers and brokers on the time, effort and expense of submitting a new application.
The dedicated new build helpline is aimed at giving brokers faster replies to queries.
Martese Carton, Leeds Building Society’s head of intermediary distribution (pictured), said: “These latest service improvements demonstrate our ongoing commitment to the new build sector and acknowledge new build purchases can often take longer to complete, particularly when buying a home off-plan.
“We continue to strengthen our new builid proposition for intermediaries, which is now led by our corporate account manager Clive Sandom, who has many years’ experience in this sector.
“Feedback from our borrowers and intermediary partners drives our service improvements and we’ve taken a number of steps in the past year to support new build.
“These include widening the range of warranties we accept, increasing LTV on new homes, introducing criteria to support modern methods of construction, and creating a dedicated new build underwriting team.”