A red line diagram is a simple map that shows the boundary of a site in a planning application. This boundary is drawn with a red line. Imagine taking a map of your property and drawing a red outline around all the land involved in your project. That red outline is what we call the red line. It marks exactly where the project will take place. If you want to build or change something on your land, you draw a red line around the area where those changes will happen.
A red line is drawn around the area that is going to be impacted by a development.
A blue line is drawn around the land that the person owns.
The Role of a Red Line Diagram in Planning
In a planning application, the red line diagram (also known as a red line plan) is very important. It tells the planning authority (like the council) which land you are asking permission to develop or change. The red line should include all the land needed for the project. This means it covers the area where you plan to build or make changes and any extra land needed for the project to work – for example, the path or driveway you will use to get into the site. In other words, the red line shows the full boundary of the project site, including things like access routes and any areas that will be affected by the work. If it's inside the red line, it’s part of your planning application; if it's outside, it’s not included.
When you submit a planning application in the UK, you normally provide this red line diagram as part of your location plan or site plan. By the time you’re using the Joe’s Blooms tool, you should have already drawn this red line in your planning documents. The council and others (like neighbours or consultants) will look at the red line to understand exactly where your project is and what land is involved. Think of it as drawing a clear box around everything that’s part of your project so there’s no confusion.
Keep the Red Line Consistent Across All Documents
It’s important that the red line you use in Joe’s Blooms is the same as the red line in all your other planning documents. Consistency matters. All your maps and plans should match up. If your architect’s drawings and your planning application forms show a certain red line boundary, then in Joe’s Blooms you need to draw that exact same line. This consistency helps everyone trust that we’re talking about the same piece of land. If the red lines don’t match, it can cause confusion or even problems with your application.
What if you decide to change the red line? Sometimes during the planning process, you might realise you need to adjust the boundary (for example, to include a bit more land). Joe’s Blooms lets you change the red line if you need to. However, if you do this, you must update all your other documents too. For instance, if you make the red line bigger in the Joe’s Blooms tool, you should also submit a revised red line plan to the council and update any related reports. All documents need to tell the same story about where your project is. Keeping the red line consistent everywhere makes sure your planning application stays accurate and avoids any misunderstandings.
Changing the Red Line for Biodiversity Net Gain (BNG)
Sometimes, people adjust their red line to help achieve Biodiversity Net Gain (BNG). There are some important things to remember if you change the red line for BNG purposes:
Include all the important areas: Make sure your red line still covers everything it needs to. This includes the land where the main work will happen, any areas that will be impacted by the project, and the access points (for example, the driveway or path to the road). Don’t leave out something crucial like the entrance or a corner of the site where work is planned. The red line should go around the entire area of development and all land needed for the project.
A bigger red line means a higher baseline: If you expand the red line to add more areas (perhaps a nearby plot where you want to plant trees or create a wildflower meadow), remember that this also adds whatever nature is already there into your project. We call the existing amount of nature the baseline biodiversity. When you include a new area, that area might have some plants or habitats already. This actually raises your starting baseline. As a result, you will need an even larger improvement to hit the 10% net gain target. Think of it like a game score – if you start at 50 instead of 40, getting 10% more means you have to score 5 points rather than 4. So, adding land can make it a bit harder to achieve the 10% gain because you’re starting from a higher number. It’s not a bad thing to include more land for nature, but be aware of this effect.
Use low-value areas to your advantage: A clever way to meet BNG goals is to include low-biodiversity areas within your red line. These are places that currently have little to no wildlife or plant value – for example, a concrete yard, a tarmac car park, or other hardstanding surfaces. Right now, these areas contribute almost nothing to nature. (In fact, surfaces like bare concrete or tarmac are usually considered to have a zero biodiversity value in the standard calculations). Because they start at zero, if you turn a paved area into a garden or plant life on it, all of that is pure gain. Including such low-value land in your site means you have a great opportunity to increase biodiversity without having to counteract much existing value. For example, transforming an old parking lot into a green space with trees and flowers will give you a big boost toward that 10% net gain. So when adjusting your red line, consider if there are any bleak, lifeless patches you can bring in and improve – it helps nature and helps you meet the target.
In summary, you can expand or tweak your red line to plan for biodiversity improvements, but do so carefully. Ensure the boundary still makes sense for the project and be mindful of how it affects your BNG calculations.
Updating Habitat Data When the Red Line Changes
Finally, remember that if you change the red line in the Joe’s Blooms tool, you must also update your habitat data for the site. The tool uses information about the types of habitats (like grassland, woodland, ponds, or hard surfaces) within the red line to calculate biodiversity values. If you add a new area into the red line, that area brings in its own habitat that needs to be recorded in the system. For instance, if you extend the red line to include an extra 100 m² of scrubland or an old paved lot, you should update the Joe’s Blooms tool to include that existing habitat in your baseline data. Keeping the habitat information in sync with your red line ensures that your biodiversity calculations are accurate and up-to-date.
Think of it this way: the Joe’s Blooms tool is like a calculator that adds up all the nature in your red line boundary. If you change the area it’s adding up (the red line), you have to tell the calculator about the new pieces or removed pieces. So always double-check your habitat entries after moving the red line. This will give you a correct baseline and a correct post-development value, which means your Biodiversity Net Gain percentage will be calculated correctly.