Drawing the red line: what to include in the site boundary

The red line boundary on a planning application defines the land the permission relates to. Draw it correctly and the consent covers everything you need to build. Draw it too tight and the access works fall outside the permission. Draw it too wide and you can tip the scheme over a threshold that brings in reports you did not budget for.

It is a two-minute drawing decision with consequences that run for the life of the scheme, and it is made by whoever happens to be producing the location plan.

What the red line legally defines

An application must be accompanied by a plan identifying the land to which it relates, under the Town and Country Planning (Development Management Procedure) (England) Order 2015. Convention, reflected in national guidance, is a location plan at 1:1250 or 1:2500 with the application site edged red, a north point, and enough surrounding context to locate it, normally at least two named roads.

The red line should include all land needed to carry out the development. That means the building, but also access from the public highway, visibility splays, parking, turning, landscaping, open space and any works needed to service the site.

The permission, if granted, authorises the described development on that land. Works outside the line are not authorised by it. This is the point most often misunderstood: a permission for a house with an access drive drawn outside the red line does not permit the drive.

The line also fixes the site area, and site area drives a surprising number of other things.

Land needed for access and visibility

Access is where tight red lines cause trouble.

Where the new access crosses land in third-party ownership, including a verge that belongs to someone other than your client, that land has to be inside the line, and an ownership certificate other than Certificate A will be required. Where the access works fall within adopted highway, practice varies. Some authorities expect the highway to be included in the red line, others do not and rely on a separate agreement under section 278 of the Highways Act 1980. Ask the highway authority before you draw it.

Visibility splays are the item most often left out. A splay extending along the frontage in both directions frequently crosses neighbouring frontages, verge or private drives. If the splay is needed to make the access safe, and the land within it has to be kept clear, it belongs inside the red line or it has to be secured another way.

The consequence of getting this wrong is not usually refusal. It is a condition you cannot discharge, or a Grampian condition preventing occupation until something happens on land you do not control.

Blue land and why it appears

A blue line is drawn around other land owned or controlled by the applicant that adjoins or is near the application site.

Its purpose is disclosure. It tells the authority what else the applicant holds, which matters for three reasons. It shows whether an apparently constrained scheme could have been laid out differently. It reveals whether a future phase is likely. And it exposes whether access or drainage could be routed over the applicant's own land instead of over someone else's.

Applicants sometimes want to omit blue land for tactical reasons. That is not a choice: the requirement is to show it, and an authority that discovers omitted ownership will not be well disposed to the application.

Where the applicant owns a large holding, mark what is relevant and adjoining rather than the whole estate. The test is proximity and relevance.

Drainage and services outside the boundary

Foul and surface water connections, attenuation, outfalls and headwalls frequently sit outside the developable area.

Three positions, and each needs a different response:

• The connection is to an existing public sewer in the adopted highway. Usually outside the red line, dealt with through the water undertaker's own consent under the Water Industry Act 1991.
• The outfall is to a watercourse across third-party land. Bring it inside the red line, with the relevant certificate, or accept a Grampian condition and the risk that goes with it.
• Attenuation is on land the applicant owns but did not intend to develop. Bring it inside the line. It counts towards the site area, which may matter for the thresholds below.

The same applies to any off-site works the drainage strategy relies on. A drainage strategy proposing an outfall on land outside the application site, with no mechanism to secure it, is the kind of gap a lead local flood authority picks up in consultation.

Consequences of drawing it too tight

A tight line looks efficient and creates four problems.

Access and visibility works fall outside the permission, as above.

Landscaping and boundary treatment on land outside the line cannot be conditioned, so the mitigation you offered cannot be secured.

Biodiversity net gain arithmetic changes. The on-site baseline is measured within the application site, so excluding a parcel removes both its baseline value and the opportunity to deliver gain on it. Where that pushes you to off-site units, the cost rises. A biodiversity net gain assessment has to use the metric completed by a competent person under the Environment Act 2021 regime, and the red line is one of its first inputs, so settle the boundary before the metric is run.

And a permission that does not cover everything built is exposed to enforcement, and shows up in due diligence on sale.

Consequences of drawing it too wide

A generous line looks safe and creates a different set of problems, mostly thresholds.

Adding half a hectare of paddock to make the plan look tidy can therefore convert a minor application into a major one, bring in a flood risk assessment, or put the scheme into environmental impact assessment screening.

Two further effects. A wider line may capture a constraint that would otherwise have been off site: a tree with a preservation order, a flood zone edge, a scheduled monument, part of a conservation area. And it draws in more land in other ownership, requiring notice on more parties, which changes who finds out about the application and when.

None of that is a reason to draw the line too tight. It is a reason to draw it deliberately, with the thresholds in front of you.

Checking the line against the ownership certificate

Section 65 of the Town and Country Planning Act 1990 and the Development Management Procedure Order require a certificate with the application. The four options are familiar:

1. Certificate A, where the applicant owns all the land in the red line and there is no agricultural tenant.
2. Certificate B, where other owners are known, and notice has been served on each of them.
3. Certificate C, where some owners are unknown despite reasonable enquiry, with notice served on those known and a newspaper notice published.
4. Certificate D, where no owners are known, with a newspaper notice published.

Owner has a specific meaning here, covering freeholders and leaseholders with a specified minimum unexpired term, and there is a separate certificate about agricultural tenants. Knowingly or recklessly issuing a false certificate is an offence.

The practical check is a three-way comparison. Overlay the red line on the Land Registry title plan for every title involved. Identify any strip, verge, accessway or rear boundary that falls outside the title. Then decide, for each, whether to move the line or serve notice.

Do it before submission. A certificate corrected during determination restarts the notice period and can reopen the consultation, and on a cross-boundary site the position is doubled, as our note on cross-boundary sites and applications to two councils explains. The decision notice and the approved plans then sit on the statutory planning register for anyone to check.

Enter your postcode on PlanScope to see which reports your site area is likely to trigger before you fix the boundary.

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.