Energy statements for change of use and conversions

An energy statement for a change of use or a conversion is a different document from one written for a new building, and the most common mistake is submitting the new-build version with the address changed. Local plan carbon policies are almost always drafted around a percentage improvement over the Part L notional building, which is a calculation designed for new construction. Apply it to a 1970s office becoming flats and the numbers either do not exist or do not mean anything.

What a council actually wants on a conversion is narrower: what the Building Regulations require for this particular change, what fabric and services improvements are feasible given the structure you have inherited, and where a policy target cannot be met, why.

Prior approval does not include energy

Start with the question that decides whether an energy statement is needed at all.

Where you are converting under a permitted development right, such as commercial to residential under Class MA or an agricultural building under Class Q, the council can only consider the prior approval matters listed in the relevant class. Those matters are specific and finite. For Class MA they cover things like transport, contamination, flooding, noise from nearby commercial premises, the provision of adequate natural light in all habitable rooms, and in some cases the loss of a ground floor use in a conservation area.

Energy and carbon are not among them. A local plan policy requiring a percentage carbon reduction cannot be applied through a prior approval, because the authority has no power to consider it.

Two things do still apply. New dwellings created under permitted development have to meet the Nationally Described Space Standard, and adequate natural light in all habitable rooms is a prior approval matter in its own right, which frequently matters more to the viability of an office conversion than any energy question.

Where you are applying for full planning permission instead, the local plan applies in the ordinary way and an Energy Statement will usually be on the validation list for anything above the council's threshold.

What the Building Regulations require

Prior approval or planning permission, the Building Regulations apply either way, and this is where the real obligations sit.

A material change of use engages requirements for the building as it will be after the works. For a conversion to dwellings that generally means insulating thermal elements where reasonably practicable, meeting the standards for controlled fittings and services being installed, and dealing with ventilation and overheating for the new residential units.

Three consequences follow for the planning submission.

Plant space and external equipment need to appear on the drawings. Air source heat pumps have external units, and their location, acoustic treatment and visual effect are planning matters even where the energy strategy itself is not.

Fabric improvements can have external consequences. External wall insulation changes elevations and reveals. Replacement glazing changes the appearance of a facade. On a building in a conservation area, that is the planning issue rather than the carbon saving.

Consequential improvements can apply to larger existing buildings undergoing certain works, which changes the scope of what has to be upgraded.

Writing the statement for an existing building

A useful conversion energy statement is short and specific. Six things belong in it.

1. A description of the existing building fabric, with measured or assumed U-values and the basis for each assumption.
2. The Building Regulations route being followed and why.
3. The fabric measures proposed, element by element, with those rejected and the reason, which will often be structural, spatial or heritage-related.
4. The heating and hot water strategy, including plant locations and any external equipment.
5. Ventilation strategy, since a tightened envelope in an existing building needs it.
6. The residual position against local policy, stated plainly.

Assumed U-values are where these documents lose credibility. If you have not opened up the fabric, say the values are assumed and say what they are based on. An assessor who assumes a filled cavity in a building that turns out to have none produces a strategy that fails on site. Opening up two or three positions before the statement is written costs very little and removes the largest source of error in the whole exercise.

Overheating, ventilation and what follows

Conversions of deep-plan commercial buildings to dwellings have a specific problem: single-aspect flats, limited openable area, and a facade that was designed for mechanical cooling.

Overheating requirements apply to new dwellings created by a material change of use, so this is not optional. An Overheating Risk Assessment using the CIBSE TM59 methodology or the simplified route in the Building Regulations should be run early, because the mitigation options touch the planning application directly. Restricting window opening for acoustic reasons and then relying on window opening for cooling is the contradiction to look for.

Where the conversion sits next to a commercial neighbour, the noise question and the ventilation question are the same question. A Noise Impact Assessment that concludes windows must stay shut has just constrained the overheating strategy, and both documents need to be written by people who have spoken to each other.

Illustrative example: a four-storey 1980s office of 1,100 m2 becoming 14 flats under Class MA. No energy policy applies through the prior approval. Building Regulations require insulation of thermal elements where reasonably practicable, and the overheating assessment shows three south-facing single-aspect units failing. The fix is external solar shading, which needs planning permission in its own right because it alters the elevation. Better to find that before the prior approval is submitted.

One further point that affects the letting model rather than the application. Minimum energy efficiency standards govern what a landlord may let, and the ratings required have been under review, so a conversion designed only to satisfy Building Regulations may still fall short of what the asset needs commercially in a few years. Design to the standard you expect to need, not the minimum you can get away with today, and check the current position before committing to a specification.

When a policy target cannot be met

On a full application where the local plan sets a carbon target, the honest route is to demonstrate the shortfall rather than to assert compliance with a calculation nobody can replicate.

Set out the target, the method used, the result, and the constraints preventing full compliance. Then show what has been done instead: fabric first within the limits of the structure, low-carbon heating, on-site renewables where the roof can take them, and any contribution the council's policy provides for. Some authorities operate a carbon offset payment mechanism for the shortfall on major development, and where one exists the policy will say how it is calculated.

A Sustainability Statement is the right place to bring the wider case together, covering water efficiency, the retention of existing structure and the reuse of materials. On a conversion, the retained structure is the strongest carbon argument you have, and it is frequently the one nobody makes.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.