Housing design standards: space, aspect and dual aspect

London housing design standards work as a set of four constraints that interact, and a layout that satisfies three of them usually fails the fourth. The national space standard sets minimum internal areas. London design policy raises the floor to ceiling height above the national figure. It also asks schemes to maximise dual aspect dwellings and to avoid single aspect flats that face north. And it limits how many dwellings can be served from one core on each floor.

Test all four at the same time, on a plan, before the massing is fixed. Checking them in sequence is how a scheme ends up with a corridor serving eleven flats, three of which face north with one window each.

Space standards applied in London

The nationally described space standard sets minimum gross internal floor areas by the number of bedrooms, bedspaces and storeys. A one bedroom one person dwelling starts at 39 square metres, or 37 where a shower room replaces a bathroom with a bath. One bedroom two person is 50 square metres. Two bedroom four person is 70. Three bedroom five person is 86.

It also sets minimum bedroom areas and widths. A single bedroom is at least 7.5 square metres with a minimum width of 2.15 metres, a double at least 11.5 square metres with a minimum width of 2.75 metres. Built-in storage is required, starting at a square metre for a one person dwelling and increasing with occupancy, and that storage counts within the gross internal area rather than on top of it.

Two things go wrong in practice. Schemes are designed to bedroom count and then described by bedspace count, which changes the applicable minimum. And storage is drawn as a cupboard with a 500 millimetre internal depth, which does not meet the standard.

State the area schedule clearly in the Design and Access Statement, with the bedroom and bedspace count, the gross internal area per unit, the standard applicable and the compliance position unit by unit. An officer should be able to check it without measuring your drawings.

Floor to ceiling height expectations

The national standard requires a minimum floor to ceiling height of 2.3 metres for at least 75 per cent of the gross internal area of a dwelling. London design policy raises that to 2.5 metres over the same proportion, and encourages greater heights at ground level in parts of the city.

The consequence is structural. Add 200 millimetres of clear height per storey to the floor zone and the services zone, and a building of six storeys grows by more than a metre. Where the height is capped by a prior approval, a tall building policy, a daylight constraint on neighbours or an agreed parameter plan, something has to give, and the thing that usually gives is a storey.

So establish the figure at the start. Check whether the borough's own plan or guidance goes further, because some do, particularly at ground floor where active frontage and flexibility are wanted.

Dual aspect and the north-facing restriction

Dual aspect means openable windows on two external walls facing different directions. That allows cross-ventilation, gives light at more than one point in the day, and gives a choice of a quieter elevation on a noisy street.

London policy asks schemes to maximise the number of dual aspect dwellings and to avoid single aspect dwellings that are north facing, that are exposed to noise levels at which significant adverse effects on health and quality of life occur, or that contain three or more bedrooms.

The design responses that work are mostly plan-form responses rather than elevational ones.

• Shorten the block depth so flats can run front to back.
• Use corner units, which are dual aspect by geometry, and plan the core so corners are maximised.
• Break a long block into linked elements with a gap, creating two external walls where there was one.
• Adopt a deck or gallery access arrangement, accepting the privacy management that brings, to give every unit two aspects.
• Place single aspect units on the south, east or west elevations and put circulation or non-habitable rooms on the north.

Where a north-facing single aspect flat is unavoidable, the justification has to be specific. Show the daylight and sunlight position for that unit, explain the ventilation strategy, and say why the plan cannot be arranged otherwise. Our note on applying BRE 209 daylight guidance in dense London covers the assessment itself, and a Daylight and Sunlight Assessment prepared by a suitably qualified author is normally expected on any scheme where the question arises.

Private outdoor space per occupant

London policy sets a minimum of 5 square metres of private outdoor space for one and two person dwellings, with an additional square metre for each further occupant, and a minimum depth and width of 1.5 metres in each direction.

That minimum dimension is the binding one. A balcony of 5 square metres at 1.2 metres deep does not comply however long it is, and a 1.2 metre balcony is also close to useless. Plan for 1.5 metres clear of the balustrade and the door swing, and check the structural edge detail, because a downstand or a thermal break can eat the dimension.

Where balconies cannot be provided, on a listed building facade or where overhang restrictions apply, the shortfall needs justification and the usual expectation is better communal amenity space, roof terraces or winter gardens. Winter gardens are treated differently in area calculations depending on whether they are counted as internal space, so state the assumption.

Core and lift ratios

The usual London expectation is a maximum of eight dwellings served from a single core on each floor. The intention is to limit the size of the shared community on a landing and to keep corridors short and naturally lit where possible.

The consequence is arithmetical and it hurts on small sites. More cores means more structure, more lifts, more plant and a worse net to gross ratio, which in turn affects viability. On a shallow plot, a single core serving eight units with four dual aspect corners is often the best available answer, and a scheme pushing to eleven units per core will be asked to justify it.

Lift provision interacts with fire strategy. London design policy expects at least one lift per core in residential development to be a suitably sized fire evacuation lift, which is physically larger than a standard passenger lift and needs a protected lobby. Settle the lift schedule with the fire engineer before the core is dimensioned. Our note on optimising site capacity under London Plan policy D3 covers how these constraints feed into the capacity argument.

Accessible and adaptable dwellings

London policy applies the optional Building Regulations access standards, with a proportion of dwellings required to meet the wheelchair user standard and the remainder the accessible and adaptable standard. The wheelchair proportion is commonly set at ten per cent, and the optional requirements only apply where a planning condition imposes them, so the condition wording matters.

Design consequences that are expensive to retrofit: level approach from the street and from parking, lift access to every storey containing a qualifying dwelling, door and corridor widths, bathroom and WC dimensions with provision for future adaptation, and accessible parking bays positioned close to the core.

Identify which units are which on the plans and in the schedule. A scheme that promises a percentage without allocating specific units creates an argument at discharge of condition stage.

Where boroughs add requirements

Borough local plans and supplementary documents add to the London position regularly: higher ground floor heights, tighter dual aspect expectations, minimum amenity space for family units, play space provision by child yield, cycle parking above the London baseline, and internal noise criteria for particular corridors.

Read the borough's plan and its residential design guidance before you draw, and read the officer reports on two or three recent comparable schemes in the same borough. Those reports tell you what the authority actually enforces, which is not always what the policy says.

This is general guidance rather than legal advice. Check the current policy wording and the current editions of the standards referred to here before relying on any figure.

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