The Mayor of London's 2026 Support for Housebuilding London Plan Guidance changes several long-standing design rules — and for anyone preparing a daylight and sunlight report, the most significant change is the withdrawal of the requirement for every new home to be dual-aspect. This article explains what the guidance does, why it matters for daylight and amenity, and what applicants should do about it.
The short version: the design standards have been loosened to help homes get built, but daylight has not stopped being a material planning consideration. If anything, relaxing the dual-aspect rule puts more weight on a robust daylight assessment to prove a scheme still works.
What the 2026 London housing design guidance changes
Published to sit alongside the London Plan and the Housing Design Standards LPG, the Support for Housebuilding guidance withdraws two rules that had shaped London residential layouts for years:
- the expectation that all dwellings should be dual-aspect; and
- the limit of eight homes per core per floor.
The stated aim is to remove design constraints that were slowing housing delivery and adding cost, while leaving the core amenity outcomes — light, ventilation, privacy and avoiding overheating — in place. In other words, the how has been relaxed, but the outcome a scheme must demonstrate has not.
Why dual-aspect matters for daylight and sunlight
A dual-aspect home has windows on two different external walls, usually facing different directions. That layout tends to deliver better daylight distribution, some sunlight for most of the day, cross-ventilation and a second outlook. A single-aspect home has all of its windows on one facade, so its light and ventilation depend entirely on that one orientation.
Single-aspect units are not banned, and never were — but they carry known risks. North-facing single-aspect flats receive little or no direct sun and can struggle against the sunlight metrics in BRE and BS EN 17037. Deep single-aspect rooms can also fail the No Sky Line (daylight distribution) test because the back of the room sees very little sky. We cover this in detail in our guide to single-aspect flats and daylight.
Daylight is still a material consideration
Loosening the dual-aspect rule does not switch off the daylight tests. Where single-aspect homes are proposed, an applicant is still expected to demonstrate that they will have adequate daylight, passive ventilation and privacy and will avoid overheating — and the guidance still asks designers to minimise single-aspect homes and to avoid single-aspect units that are north-facing, exposed to noise, or have three or more bedrooms.
Underneath the London-specific policy, the assessment framework is unchanged. Daylight and sunlight are judged against the BRE BR 209 (2022) guide, used together with BS EN 17037 for internal daylight provision, and read through the relevant London Plan housing-quality policy on daylight and amenity. If you need a refresher on how those two standards fit together, see our explainer on BR 209 and BS EN 17037 in one report, and our overview of London Plan daylight standards in 2026.
What this means for your scheme
The practical effect is that more London schemes can now propose layouts that would previously have been resisted — more homes per core, and a higher proportion of single-aspect units on constrained sites. That flexibility is genuinely useful. But it shifts the burden of proof onto the daylight and sunlight evidence:
- Single-aspect units need to be justified with numbers. A planner is far more likely to accept single-aspect homes when a daylight report shows the rooms meet target illuminance under BS EN 17037 and that any north-facing or deep-plan units have been tested honestly.
- Orientation still drives outcomes. Relaxing the rule does not change physics — a north-facing single-aspect living room will still under-perform on sunlight. Testing early lets you re-plan before you are committed.
- Amenity space and overshadowing still count. Communal gardens and balconies are assessed for sunlight using the BRE overshadowing test, unaffected by the design-guidance changes.
Our strong recommendation is to run a daylight and sunlight appraisal at concept stage, not after the layout is fixed. Early testing is how you take advantage of the new flexibility without walking into a refusal on residential amenity grounds. Our guide on passing a BRE daylight assessment first time sets out the design moves that help most.
Does this apply outside London?
The Support for Housebuilding guidance is a London document, tied to the London Plan. Outside London, daylight is handled through each authority's local plan amenity and design policies, with the same national framework — the NPPF — and the same BRE and BS EN 17037 technical basis. The London change is a useful signal of the direction of travel nationally, where housing delivery is being prioritised, but it does not itself alter policy elsewhere.
How Fortress Associates can help
Fortress Associates prepares BRE 2022 and BS EN 17037 daylight and sunlight reports for planning applications across the UK. Whether you are testing a single-aspect layout in a London borough or an extension in a two-tier district, we assess VSC, No Sky Line and APSH for neighbours and internal daylight for new homes, and set out mitigation where a scheme falls short. Reports are typically delivered in 4–5 days with no advance payment. To discuss a scheme, get in touch or see the full range of our planning services.
Sources & further reading
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