Solar arrays on higher risk buildings and the fire case

Putting a photovoltaic array on the roof of an 18 metre residential block sets two planning policies against each other. Carbon policy wants the generation. Fire policy wants a simple, uncluttered roof with clear access and no additional ignition sources above the highest occupied storey. Neither policy yields, so the application has to reconcile them with evidence rather than assertion, and the place that happens is the fire statement submitted at Planning Gateway One.

The scheme most likely to stall is the one where the energy strategy was fixed before the fire engineer was appointed.

Which buildings this applies to

Planning Gateway One applies to relevant buildings under Article 9A of the Town and Country Planning (Development Management Procedure) (England) Order 2015. In broad terms that means buildings of 18 metres or more in height, or seven or more storeys, containing at least two residential units, together with care homes and hospitals meeting the same height test.

For those buildings a Fire Statement must accompany the planning application on the published form, and the Health and Safety Executive, acting as the Building Safety Regulator, is a statutory consultee. Fire Statements require a professional with the necessary fire engineering competence to author them under the Building Safety Act 2022 framework, and an AI-assisted draft is a starting point for that professional rather than a substitute for them.

The definition of a higher-risk building for the wider building safety regime sits in secondary legislation made under the 2022 Act, and height is measured in a specified way that does not always match the figure on a planning drawing. Confirm the measurement method before assuming a building falls outside the threshold by a few hundred millimetres.

Why a roof array attracts questions

Roof mounted arrays introduce three things a bare roof does not have: a direct current electrical installation that remains live while the sun is up, combustible components in the form of cabling, backsheets and mounting materials, and a physical obstruction across the roof plane.

None of those is a reason to refuse. Each is a reason to be asked a question, and the questions tend to arrive in the same order.

How will the array be isolated in an emergency, and where is the isolation point. How does a firefighter reach a fire beyond the array. What is the separation between the array and any roof-level plant, means of escape, smoke shaft head or lift overrun. What prevents fire spreading under the panels along the mounting system. And how is any cabling routed so it does not pass through protected shafts or compartment lines.

Answer those five in the fire statement and the consultation usually proceeds without a holding response.

The combustible materials question

Regulation 7 of the Building Regulations 2010 restricts the use of combustible materials in the external walls of relevant buildings and in specified attachments to them, with a list of exempt components. Whether a particular photovoltaic installation is caught depends on where it is fixed, because a roof plane and an external wall are treated differently and a facade-mounted array raises issues a roof array does not.

Check the current consolidated text rather than working from recollection. The restriction has been amended more than once, and the list of exempt components is the part most often misremembered. Where there is doubt, the right course is for the fire engineer to state the interpretation relied on in the statement, so the regulator can engage with it at Gateway One rather than at Gateway Two when the design is frozen.

Facade-integrated systems, solar shading and balcony-mounted panels all sit closer to the restriction than a ballasted roof array, which is one reason roof mounting remains the default on tall residential buildings.

Access, maintenance and the space the array takes

On a low building the maintenance strategy for an array is a ladder and a safety line. On a 20 storey block it is a permanent access arrangement, and that arrangement competes for roof area with everything else the building needs up there.

Plan the roof as a layout drawing at application stage, showing the array, the maintenance zones, the mansafe system anchor lines, the smoke shaft head, the lift overrun, the plant enclosure, the window cleaning equipment and the clear route from the roof access door to each of them. A roof plan that shows panels covering the whole plane with a note saying access will be agreed later is the kind of drawing that generates a request for further information.

Firefighting access is a separate consideration from maintenance access. The fire and rescue service will want to understand how the roof is reached, what the array does to that route, and whether the array would be left in place or made safe during an incident. Those questions belong in the Fire Safety Strategy, which is a fire engineering document requiring a competent professional author, with the planning-stage principles summarised in the fire statement.

Reconciling the carbon case with the fire case

The honest position is that a tall residential building has a poor roof-to-floor-area ratio, so a roof array on a slender tower contributes a smaller proportion of the building's demand than the same array on a two storey block. That weakens the argument for covering every square metre and strengthens the argument for a smaller, well organised array that leaves the roof workable.

Three moves usually resolve the tension.

1. Size the array to the space that remains after fire, access and plant requirements are laid out, rather than laying out the array first.
2. Move generation off the roof where the site allows, using canopies over parking, podium decks or lower blocks within the same development, all of which are easier to access and sit below the height threshold that drives the fire questions.
3. Shift the carbon strategy weight towards fabric and heat pumps, and show the revised balance in the Energy Statement so the council can see the generation reduction has been compensated rather than simply dropped.

Where a policy sets a fixed on-site reduction percentage, set out the constraint and the offset arithmetic in the same document. A planning committee can accept a shortfall it understands. It reacts badly to a shortfall it discovers.

What the fire statement should actually say about the array

The form asks about principles rather than detailed design, so the array section should be short and specific. Include the proposed location and extent of the array on a roof plan, the mounting method and whether it is ballasted or fixed, the isolation arrangement and the location of any firefighter switch, the separation distances to roof-level openings, plant and escape routes, the maintenance access strategy, and the cable routing principle including where cabling crosses compartment lines.

Say what has been assumed and what remains to be confirmed. A statement that flags an open item and names the standard it will be resolved against reads as competent. One that is silent on isolation reads as incomplete.

Structural implications belong in the same conversation, since ballast adds load and wind uplift on a tall building is severe. Where the frame is being designed to resist disproportionate collapse, the array and its ballast are part of the loading case, which is covered in disproportionate collapse and building class in design.

Conditions worth proposing

Planning conditions cannot resolve fire engineering, and they should not try. What they can do is hold the design position that the Gateway One consultation was based on.

A condition requiring the roof layout to be built as approved, with any change to the array extent or location submitted for approval, prevents the array quietly expanding into the maintenance zone during value engineering. A condition requiring details of roof-level plant and enclosures, including their relationship to the array, keeps the two coordinated. And a condition requiring evidence of the installed generation capacity before first occupation gives the energy strategy something to be measured against.

Appoint the fire engineer before the energy strategy is fixed, not after. Where a reviewer is needed to check a draft before submission, the professional directory is the route to someone who can take that responsibility.

This is general guidance, not legal advice. Check the position with your local planning authority, the Building Safety Regulator 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.