Letchworth Garden City Heritage Foundation’s solar rules contain a line that most towns’ rules do not: where one half of a pair of semis already has panels, the Foundation expects the other half’s arrangement to mirror it. In a town where a quarter of households live in a semi, that makes the roof next door part of your design brief before anyone has looked at your own.
This guide covers what that means in practice, alongside the Foundation’s other layout rules, the two Character Areas, and what happens when you want to extend an array that is already up. For generation, cost and the wider planning picture, see our page on solar panels in Letchworth Garden City.
How many arrays are already up
DESNZ records about 4,214 solar PV installations across North Hertfordshire at the end of 2025, with 43.22 MW of capacity. That is a district figure, covering Hitchin and the villages as well as Letchworth, and it counts every size, from a terrace roof to a solar farm, so it is not a count of homes. DESNZ also notes that many 2025 installations could not yet be assigned to a council area when the figures were first published, so the count is likely to rise. Locally, the point is simple: the chance that the other half of your Letchworth semi, or the terrace next door, already carries an array is real, and the Foundation’s rules take it into account.
The mirror rule for semis
At the 2021 Census, 25.0% of households in Letchworth’s built-up area lived in a semi-detached house. For those homes, page 8 of the Foundation’s May 2026 principles is the one to read. Where one property in a semi has already installed panels, it expects to see the same arrangement mirrored, preserving the symmetry of the pair. It also encourages semi-detached neighbours to work together on a single, symmetrical array.
In practice that changes the order of work. The survey starts on the neighbour’s roof as well as yours: the number of panels, their rows, their position on the slope and their colour. If next door has no panels yet, the Foundation’s encouragement points the other way, and a conversation over the fence before either of you applies can save a redesign later. Where the existing array looks unlike today’s principles, ask the Foundation’s Heritage and Stewardship team how it wants the pair handled. Its pre-application advice is given at no charge.
The layout rules every array meets
Whatever the house type, the principles ask for panels grouped in one orderly array, rectangular where possible, all the same size and orientation. They should be set in from the edges of the roof rather than overhanging it, and preferably black, frames included. Terraced houses are Letchworth’s largest group, 33.3% of households, and while the mirror rule is written for semis, the same layout rules apply to a terrace roof, so an array is designed to sit tidily among its neighbours’ slopes, not just within its own.
Heritage or Modern Character Area
The principles divide the town in two. In the Heritage Character Area, which includes Homes of Special Interest, panels must be on rear elevations and not visible from the public realm. In the Modern Character Area, panels are acceptable on any roof slope, provided the other requirements are met. So on a Heritage Character Area semi, mirroring next door usually means mirroring a rear array, and the back roof sets the size of both. The Energy Saving Trust’s typical system is around 4.5 kWp, about 12 panels over 20 to 30 m² of roof; a Letchworth rear slope may take fewer, and the survey settles it.
Extending an array you already have
Adding panels to an existing array is a new external alteration, so under the Scheme of Management most homes need the Foundation’s prior written consent again; leaseholders also need consent under their lease. The extended array still has to read as one orderly group, which in practice means panels of the same size and orientation as the ones already up.
The network counts the whole system too. Letchworth’s town centre sits in UK Power Networks’ Eastern Power Networks area. Type-tested generation up to and including 16 A per phase (3.68 kW) is notified under G98, before commissioning or within 28 days after it; above that, a G99 application must be approved before work starts, and a 4 kW inverter, at 17.39 A, is just over the line. UK Power Networks says it automatically approves an application where the maximum export, after any export limitation, is under 5 kW. A residential solar installation, extensions included, carries 0% VAT until 31 March 2027, then 5%, as our guide to VAT on solar panels and batteries explains.
And if it is a battery you want to add
A battery is ancillary equipment under the Foundation’s principles: it needs consent and must not be visible from the public realm, which usually means indoors. Our guide to adding a battery to Letchworth panels you already have covers that route, and our page on battery storage in Letchworth Garden City covers where a unit fits.
Who applies
Ownership decides who makes the application. 30.1% of households in Letchworth’s built-up area rent from a social landlord and 11.6% rent privately or live rent-free, so for about four homes in ten the landlord decides first (our arithmetic). Planning is a separate, usually simpler question here: North Herts Council’s two Article 4 directions are for Hitchin and Stockens Green, not Letchworth, and roof slopes in the town’s conservation areas stay permitted development. For the same questions in neighbouring towns, see our solar panels in Hertfordshire hub.
Sources: Letchworth Garden City Heritage Foundation, Solar Panels in Letchworth Garden City: Design Principles (revised May 2026), pp.2, 3, 6 and 8; DESNZ, Renewable electricity by local authority, 2014 to 2025 (published 29 September 2026), North Hertfordshire; ONS, Towns and cities, characteristics of built-up areas, Census 2021 (tables 5c and 6c); Energy Saving Trust, Solar panels: costs, savings and benefits explained (updated 27 August 2026); UK Power Networks, licence boundaries open dataset (17 December 2024) and Solar and storage: cost, time and what’s involved; Energy Networks Association, EREC G98 Issue 2 (10 March 2025); HMRC, VAT Notice 708/6; North Herts Council, About conservation areas and Article 4 directions (updated 4 August 2026) and Letchworth Conservation Area page; legislation.gov.uk, GPDO 2015 Schedule 2 Part 14 Class A as amended by S.I. 2026/896.