Housing quality standards: dual aspect and north facing

Policy D6 of the London Plan 2021 sets the housing quality standards that a London residential layout has to meet, and two of them do more to shape a plan than all the others combined: the position on single aspect dwellings and the floor to ceiling height. Get those wrong at concept stage and the unit mix, the core count and sometimes the building depth all have to change.

The policy is a layout test rather than an area test. Space standards are easy to check and easy to design to. Aspect and orientation are properties of the plan form, so they cannot be fixed by making rooms slightly bigger.

What the policy says about single aspect units

D6 does not ban single aspect dwellings. It says that single aspect dwellings which are north facing, which have three or more bedrooms, or which are exposed to noise levels above which significant adverse effects on health and quality of life occur, should be avoided.

Read that as three separate tests on the same unit type. A south facing single aspect one bedroom flat on a quiet street passes all three. A north facing single aspect three bedroom flat fails two of them, and no amount of internal area compensates.

The practical consequence is that a double-loaded corridor building with units on both sides will always produce a cohort of single aspect flats, and the orientation of the building then decides whether half of them are acceptable. That is a massing and orientation decision made at the first sketch, which is why the aspect schedule should be produced from the earliest test plans rather than at submission.

North facing single aspect and the presumption against it

The London Plan does not define the arc that counts as north facing, and boroughs fill the gap in their own guidance. A common approach is an arc either side of true north, often 45 degrees, measured from the outward normal of the window wall. Some boroughs apply a narrower arc, and some assess the sunlight received rather than the compass bearing.

So the first thing to do on a scheme is to find out which test the borough applies. Designing to 45 degrees and then meeting an authority that measures sunlight hours on the window wall is an expensive discovery.

Where north facing single aspect units cannot be avoided entirely, the arguments that carry weight are specific rather than general. Increasing the glazed area and ceiling height, giving the unit a wider frontage and shallower depth, providing a generous balcony that does not itself block light, and demonstrating acceptable internal daylight under BS EN 17037 all help. The daylight guidance applied to dense London sites matters here, because the internal assessment is the evidence that the unit works.

An honest caution: a handful of north facing single aspect units in a large scheme is usually negotiable, and a scheme where they are the predominant type is not.

Dual aspect and how it is measured

The London Plan treats a dual aspect dwelling as one with openable windows on two external walls, which may be opposite each other or on adjacent walls. That adjacent case is where most disagreement arises, because a corner unit with windows 10 degrees apart on a shallow splay is not providing cross ventilation or two light sources.

Boroughs commonly expect the two elevations to be meaningfully different in orientation. Some set a minimum angle. When you present the aspect schedule, state the rule you have applied and show it on the plans, because an officer who recounts your dual aspect units on a different basis will arrive at a different percentage and will trust the rest of the schedule less.

Three design moves generate genuine dual aspect in a deep plan:

• Corner units at every core, which is the least costly source of dual aspect in a point block.
• Through units spanning the depth of the building, which works where the building is shallow enough for a reasonable room sequence.
• Recesses or lightwells of sufficient width to give a second useful outlook, rather than a token window into a 2 metre slot.

Minimum floor to ceiling heights

D6 requires a minimum ceiling height of 2.5 metres for at least 75 per cent of the gross internal area of each dwelling. That is higher than the 2.3 metre figure in the Nationally Described Space Standard, and it has a direct cost in building height.

Work it through early. On a nine storey block, the difference between a 2.5 metre and a 2.4 metre clear height, with the same floor zone, is close to a metre of building height, which can push the scheme over a height threshold in a local policy or into a different consenting route.

The 75 per cent allowance gives room for a lowered zone over a bathroom or a hallway where services run. Use it deliberately and show it on a section, because a scheme that relies on the allowance without identifying where it applies invites a condition requiring the matter to be resolved later.

Core counts and dwellings per core

D6 expects no more than eight dwellings to be accessed from a single core per floor. On a deep plan with a long corridor, that limit bites quickly, and the answer is usually more cores rather than fewer units.

More cores costs gross internal area and affects the efficiency ratio, so it belongs in the appraisal rather than in a late value engineering exercise. It also interacts with fire strategy and with the way a scheme optimises its capacity, and the design led approach to site capacity is the right framing for that conversation with officers.

Private outdoor space standards

Every dwelling should have private outdoor space, with a minimum of 5 m² for one and two person dwellings and an additional 1 m² for each further occupant. Balconies and other private external spaces should have a minimum depth and width of 1.5 metres.

That 1.5 metre dimension is the one that catches schemes out. A 1.2 metre deep balcony, however long, does not meet it, and a recessed balcony with a 1.4 metre clear depth after the balustrade zone does not either. Dimension the clear usable area on the plan rather than the structural opening.

Where private space cannot be provided for a particular unit, the policy allows the shortfall to be addressed through other amenity provision, and the case has to be made rather than assumed. Communal and child play space sit alongside this, and a Play Space Assessment is normally needed once the child yield reaches the threshold in the plan.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and verify the current London Plan text, which is under review.

Testing a layout before submission

Build one schedule and keep it as the single source of truth for the design team. One row per unit, with these columns:

1. Unit reference, core and floor.
2. Bedroom and person count, and gross internal area against the space standard.
3. Aspect, recorded as single or dual, with the rule applied.
4. Orientation of the principal window wall in degrees.
5. Private outdoor space area with clear depth and width.
6. Proportion of gross internal area at 2.5 metres clear height or more.
7. Dwellings accessed from that core on that floor.

An illustrative example

A 96 unit scheme in three cores produces 38 single aspect units on a first test plan, of which 11 face within 45 degrees of north and two of those are three bedroom. Rotating the block 18 degrees and converting two end bays into through units reduces the north facing single aspect count to four one bedroom flats, all with internal daylight above the target in the national annex to BS EN 17037. This example is illustrative rather than a real scheme.

Run that schedule at every design stage. The number that officers ask for first is the proportion of single aspect units, and a scheme that can answer it in one line, with the rule stated, starts the conversation in a better place.

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