Design code: what it fixes and what it leaves open

A design code is a set of illustrated, measurable rules for how development should be built in a defined area. It fixes the things that determine whether a street works, such as building lines, plot widths, storey heights, boundary treatments and street dimensions, and it leaves alone the things that do not, such as internal layouts and the detailed architectural expression within an agreed palette. The distinction between those two categories is what makes a code useful rather than merely long.

Architects encounter codes in three forms: an authority-wide code adopted by the council, an area code covering a town centre or an urban extension, and a site code prepared alongside an outline application and used to judge the reserved matters. Each carries different weight and each constrains you differently.

Codes at three scales

The Levelling-up and Regeneration Act 2023 introduced a requirement for local planning authorities to prepare design codes covering their areas, alongside the framework in the National Model Design Code. That produces a hierarchy.

An authority-wide code sets principles and area types across the district, usually at a level of detail that shapes rather than determines a scheme. An area code applies to a defined place, often a growth area, a high street or a neighbourhood with a distinct character, and it will carry specific parameters. A site code is prepared for a single development, frequently by the applicant, and is the most detailed of the three.

The National Model Design Code sets out the process for preparing these: analysing the area, defining area types, then coding each area type against the ten characteristics of good design used in the National Design Guide. Codes that skip the analysis stage and jump to parameters tend to produce rules that fit nowhere in particular.

The parameters a code usually fixes

Coded parameters divide into a few families, and most codes touch all of them.

• Movement and street type, covering carriageway and footway widths, corner radii, on-street parking arrangement, cycle provision, street tree spacing and the treatment of junctions.
• Block and plot, covering perimeter block dimensions, plot widths, building lines and setbacks from the back of footway, and the position of parking within the plot.
• Built form, covering storey heights, floor to ceiling dimensions, roof form and pitch range, eaves lines, and where taller elements may sit.
• Frontage and threshold, covering entrance position, door and window proportions, reveal depth, boundary walls, railings and hedge heights.
• Materials, usually as a palette with permitted and excluded options rather than a single specification.
• Nature and public space, covering tree canopy targets, front garden planting, sustainable drainage in the street, and the typologies of open space.

Reveal depth is the parameter that repays attention. It is a small dimension, it is the first thing value-engineered out, and it does more for the appearance of a brick elevation than almost anything else a code can require.

What a code leaves open

A well-drafted code says what it does not control, and the list is longer than people expect.

Internal planning, room sizes above the applicable standards, structural system, servicing strategy and tenure are usually outside the code. So is detailed architectural expression, provided it sits within the palette and the coded proportions. Many codes also leave innovation open by allowing a departure where an applicant demonstrates the design meets the objective the parameter was serving.

That last point is the difference between a code that produces good places and one that produces uniform ones. A code which fixes the building line, the eaves height and the palette, and then allows the architecture to vary within them, is doing its job. A code that specifies window head details across 400 homes is not.

Codes also use a graded language, typically distinguishing between what must be done, what should normally be done, and what could be done. Read which grade applies to each parameter before deciding what is negotiable.

How much weight a code carries

Weight depends on how the code was adopted, not on how detailed it is.

The last row is the one that catches people. A site code approved under a condition on an outline permission becomes the standard against which reserved matters are judged, so an applicant who drafts a code loosely gains flexibility, and one who drafts it too tightly has to apply to vary it later. The question of how binding a code is in practice is covered further in design codes in planning and how binding they are.

Departing from a code

Departure is normal and codes should anticipate it. The argument that works is not that the parameter is inconvenient, but that the objective behind the parameter is met another way.

So: the code requires a 2m front setback to create a defensible threshold. Your corner unit has its entrance on the flank, with a walled garden addressing the primary street. The threshold objective is met by the wall, so the setback is unnecessary here. That argument succeeds. The argument that the setback loses saleable floor area does not.

Set this out in the Design and Access Statement, parameter by parameter, with a compliance schedule listing each coded requirement, whether the scheme complies, and where it does not, why the objective is still achieved. Officers and design review panels respond well to that format because it saves them building the schedule themselves, and it is the same discipline a design review panel will apply.

Preparing a site code with an application

Where you are writing the code rather than following one, three decisions shape everything.

First, decide what really has to be fixed to secure the character you are promising, and code only that. Every additional parameter is a future variation application.

Second, write the parameters so they can be tested. "Buildings shall address the street" cannot be assessed. "The principal entrance shall be located on the primary street elevation and be visible from the footway" can.

Third, include the illustrations. A code without drawings and photographs is a specification, and it will be read differently by every person who picks it up. Coding plans showing which parameters apply where are the part officers use most.

State clearly how the code relates to the development plan and what happens where they conflict, and set out the process for agreeing departures. The Planning Statement should explain that relationship rather than leaving the reader to work it out.

Codes compared with design guides

A design guide is qualitative and illustrative. It explains what good looks like, shows precedents and expresses preferences, and it is used to inform a judgement.

A code is specific and measurable, and much of it is expressed as requirements rather than preferences. You can test compliance with a code using a tape measure and a materials schedule. You cannot test compliance with a guide in the same way, which is the reason national policy has pushed towards coding.

Both can sit in the same document family, and many authorities publish a guide that sets out the reasoning and a code that sets out the rules. When you are handed one, check which you are holding before you price the design work.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.