The energy hierarchy on a small residential scheme

A two house scheme does not need a forty page energy statement, and submitting one usually means the wrong document has been copied from a major application. The energy hierarchy small scheme question is really about proportion: the same three steps apply, but on a minor residential development two of them resolve in a paragraph each and the third carries the whole argument.

Be lean, be clean, be green. Fabric and demand reduction first, efficient supply second, renewable generation third. Local plan policies use that sequence because it puts the measures that last for the life of the building ahead of the ones that get replaced.

What the hierarchy asks at each step

Being lean means reducing the demand for energy before you supply any. Insulation levels, airtightness, thermal bridging, window area and orientation, shading, and the size and shape of the building itself.

Being clean means meeting the remaining demand efficiently, historically through connection to a heat network or on site combined heat and power. On a scheme of one to nine dwellings this step usually resolves quickly, because no network is available and a small combined heat and power unit makes no sense. Say that in one paragraph with the evidence, rather than omitting the step, because an officer checking against policy wants to see it addressed.

Being green means renewable generation on the site. Photovoltaics in most cases, heat pumps where they are counted here rather than under the clean step, and occasionally solar thermal or a small wind installation on a rural plot.

Order matters for a practical reason. A poorly insulated house with a large photovoltaic array uses more energy for its life than a well insulated one with a smaller array, and only one of those two measures is hard to change later.

Fabric measures that matter most at small scale

On a small scheme the fabric decisions with the largest effect are not always the ones with the highest specification.

Thermal bridging is the one most often left as a default. Using accredited construction details, or calculated psi values for the junctions actually being built, routinely changes the result more than an incremental improvement in wall U value. Junctions at the eaves, at window reveals and at the ground floor perimeter are where the heat goes.

Airtightness is the second. Every new dwelling is subject to air permeability testing under the current Approved Document L, and a design target well below the backstop figure is achievable in masonry and timber frame alike with attention to the sequence of the air barrier rather than to expensive products. What it requires is a drawn air barrier line on the section, agreed with the contractor before work starts.

Form factor is the third, and the one nobody wants to hear. A compact two storey form loses less heat than the same floor area spread across a single storey with three external wall returns. On a self build with the plan still fluid, that is a free saving.

Then glazing. Window area on the north elevation costs heat in winter and delivers little; on the south it delivers useful gain in winter and an overheating risk in summer, which Approved Document O now tests for new dwellings. Balancing those two is the design work, and it is much easier before the plan is fixed.

Efficient supply where no network exists

For a minor scheme, the honest answer is usually that there is no heat network within a workable distance and no basis for on site generation, and the efficient supply step is therefore met by the choice of heating system.

Evidence the point rather than asserting it. Name the nearest existing or planned network, or state that the local authority's heat mapping shows none in the area, and give the distance. Where a network exists but is not accessible, say why, with the connection route and the capacity position.

An air source heat pump meets the step in most local plan wordings, because it converts electricity to heat at an efficiency above unity and the grid electricity it uses continues to decarbonise. Where a gas boiler is proposed, expect that choice to be tested, and the reasoning behind it is set out in our note on the all electric new homes gas connection decision.

Renewables sized to the roof available

The green step is where numbers are expected, and where a major scheme template produces nonsense on a small site.

Size the array to what the roof can actually carry after everything else is on it. The variables:

• usable roof area after rooflights, flues, vents and any plant
• pitch and orientation, with south to west facing planes performing best
• shading from trees, chimneys and neighbouring buildings across the day and the year
• structural capacity of the roof as designed
• inverter and connection constraints

That last point catches people. Connecting a generator to the distribution network has notification thresholds, and a small installation can normally be connected under a simple notification while larger arrays need an application to the network operator before installation. Check it early on a multi plot scheme, because a group of houses each with a substantial array can add up to a connection that needs agreement.

State the array output in kilowatts peak (kWp), the estimated annual generation and the proportion of the scheme's regulated energy demand it covers. Three numbers, with the assumptions behind them.

Reporting results proportionately

For a scheme of one to nine dwellings, a document of six to ten pages usually covers everything an officer needs.

1. The scheme, its floor areas and its heating strategy, in half a page.
2. The lean measures, with the U values, the airtightness target, the thermal bridging approach and the overheating strategy.
3. The clean step, with the heat network evidence and the system choice.
4. The green step, with the array size, generation and coverage.
5. The resulting compliance position against Part L, from the design stage calculations, with the software and version named.
6. The policy position: which local plan policy applies, what it requires numerically, and how the scheme meets it.
7. A short table summarising the figures.

That last table is the part officers read. Put it early. The supporting calculations belong in an appendix, and the narrative belongs in an Energy Statement rather than being spread across the design and access statement and a covering letter.

Avoiding a document written for a major scheme

Three markers give away a borrowed template, and officers spot all three.

References to policies that apply only to major development, particularly carbon offset payment mechanisms and monitoring requirements that are triggered by scale. A whole life carbon section on a two house scheme where no policy requires one. And a district heating feasibility study running to several pages on a site where the nearest network is 12 kilometres away.

The opposite failure is a document of two paragraphs asserting compliance with no figures. Between those, the test is simple: can an officer read the document and verify each policy requirement against a number in it. If yes, the length is right. A broader Sustainability Statement covers the non energy policies, and keeping the two separate makes both shorter.

What the council will condition

Expect conditions rather than a clean permission, and expect them to bind the specification you relied on.

Typical wording requires the development to be built in accordance with the approved energy statement, the renewable installation to be operational before occupation, and evidence to be submitted. Some authorities require the as built calculations and the airtightness test results to be provided at completion, and a few require a photograph of the installed array.

The failure that surfaces at discharge stage is substitution. A specification is value engineered during construction, the as built calculation no longer matches the approved one, and the condition cannot be discharged without a variation. Where a change becomes necessary, deal with it while the scheme is on site rather than at the point of sale, when a buyer's solicitor asks for the discharge notice and finds an outstanding condition.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Part L compliance calculations need to be produced by a competent assessor. This is general guidance and not legal advice, so check the position with your local planning authority or a qualified professional before relying on it.

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