Northumberland County Council’s aspiration for new homes to be as green as possible could be undermined by a lack of evidence on the cost.

Concerns were raised by planning inspector Susan Heywood in relation to viability as the second phase of hearings for the examination of the Northumberland Local Plan got underway.

The first session, held last Tuesday, dealt with the quality of place section, with the policy relating to sustainable design and construction causing the biggest stumbling block for the council, despite amendments.

It seeks to ensure that, where feasible, new developments are as environmentally friendly as possible through the inclusion of passive design measures for heating, small-scale renewable and low-carbon energy generation, water efficiency measures, and the use of locally sourced, recycled and energy-efficient building materials.

Representing the local authority, Zoe Charge said the measures were included as part of the overall viability assessment – to ensure that homes are deliverable with all of the additional requirements – and that many of them are cost-neutral.

But under questioning, she later added: “We haven’t explicitly tested any of these, but it’s on a sound basis we consider them to be cost-neutral.”

When the inspector pointed out that they aren’t all cost-neutral, Ms Charge responded: “No, but we have added that flexibility (of them being delivered ‘where feasible’). We have a statutory duty to address climate change.”

Nicola Reed, from Persimmon Homes, said it was ‘slightly concerning’ that the non-cost-neutral elements hadn’t been included in the viability assessment.

Chris Martin, from the Pegasus Group, representing Gleeson, added: “We are quite surprised some of these haven’t been included in the viability assessment. A few of the things deemed to be cost-neutral, I would question whether they really are. “It’s not just about feasibility, it’s about affordability and deliverability of sites.”

In response, Ms Charge said: "This is a requirement of the National Planning Policy Framework that should strive to achieve this."