Solar panels and building work: lofts, extensions and new roofs
If the roof is coming off, the scaffolding is going up or the walls are open for rewiring, that is the cheapest moment to plan for solar panels. Here is what the planning and building rules say, what to agree with your builder, and what changed in 2026.
In the news
In January 2026 the government published its £15bn Warm Homes Plan (BBC News), with grants and low- and zero-interest loans for solar panels, batteries and heat pumps in existing homes — the full plan is on GOV.UK.
In March 2026 it confirmed the Future Homes Standard (BBC News): from 24 March 2027, with a 12-month transition, new homes in England must generate renewable electricity on site and use low-carbon heating. The legal detail is in Building Circular 01/2026 and the minister’s written statement to Parliament.
The new-build rule does not reach extensions or refurbishments. But it is a clear sign of where the Building Regulations are heading, and a good reason to leave room for panels when you build now.
Why building work is the moment
The Energy Saving Trust notes that installation costs less if scaffolding is already up for roof repairs, and that renewing the roof covering is sometimes recommended before panels go on so the roof stays watertight for the life of the system.
A loft conversion or rear extension also redesigns the roof structure. The Planning Portal says the roof’s ability to carry the weight of panels has to be checked and proven, and that some strengthening may be needed — far easier to allow for on the drawing than to add afterwards.
Then there is the wiring. Panels need a cable route down to an inverter and the consumer unit, and a battery needs a suitable spot with access for maintenance. Running those routes at first fix, before the plaster goes on, costs a fraction of chasing them into finished walls later.
What to plan with your builder
- The roof area you will keep clear. Dormers, rooflights and soil vent pipes all eat into the unbroken slope panels need, ideally facing south, east or west.
- The structure. Ask for the panel load to be included when the roof and any steels are designed.
- The cable route and inverter position. A clear run from the roof to where the inverter and consumer unit will sit, decided at first fix.
- Space for a battery. Often a loft, utility room or garage wall, with access for maintenance.
- Scaffolding. If you are fitting panels at the same time, line the solar installer up to use the builder’s scaffold.
- The roof covering. If it is near the end of its life, renew it before panels go on.
Your builder handles the structure and the openings; an MCS-certified installer designs and fits the solar system itself. Getting the two talking before the drawings are fixed is most of the battle.
Do you need planning permission?
For a house in England, roof-mounted solar panels are normally permitted development. The conditions are set out in Part 14, Class A of the General Permitted Development Order:
- panels on a pitched roof must not protrude more than 0.2 metres beyond the roof slope;
- they must not be higher than the highest part of the roof;
- they should be sited, so far as practicable, to minimise their effect on the external appearance of the building, and removed when no longer needed;
- listed buildings are excluded, and in conservation areas panels cannot go on a wall that fronts a highway.
Councils can also remove permitted development rights with an Article 4 direction. In Lewisham, for example, alterations to the roof of a house covered by a direction need planning permission. If you are in a conservation area, check with the council before you commission anything.
Help with the cost
The Warm Homes Plan brings government-backed low- and zero-interest loans for solar panels, batteries and heat pumps, and fully funded packages for low-income households. Under the Warm Homes Loan Scheme rules, financed panels must be MCS-certified products fitted by an MCS-certified installer, and scaffolding for the solar installation counts as part of the eligible cost.
Installing solar panels in a home is currently zero-rated for VAT until 31 March 2027. To see what a system would save you, run your numbers through our solar panel savings calculator.