Planning Guides
Extensions
2025-08-07 | Alejandro Trinco
Beyond the Red Line: Landscaping for Planning Success
You've designed the perfect extension, but have you considered the garden? Simply paving over the lawn for a new patio can trigger a planning refusal. Councils now scrutinise landscaping for its impact on flood risk and, crucially, Biodiversity Net Gain (BNG). This guide explains why your garden is now a critical part of your application and how a smart landscaping plan can actually help you secure that coveted planning permission.
Jurisdiction: England.
The Application Is More Than Just the Building
TL;DR: Your Whole Site is Being Assessed
The "red line" on your planning application map defines the site the council will assess, including your garden.
Large areas of new, non-permeable paving can be a valid reason for refusing an extension.
Key planning concerns are flood risk, loss of garden amenity, and since April 2024, Biodiversity Net Gain (BNG).
A thoughtful landscaping plan can solve these issues and strengthen your application.
For most homeowners, an extension project is all about the building. You spend months finalising the internal layout, the window styles, and the brick choices. The garden is often an afterthought: "We'll just pave that muddy patch for a low-maintenance patio." This seemingly harmless decision can be a critical mistake. When you submit a planning application, the council's assessment doesn't stop at your back door. They are legally required to assess the impact of the entire development within the red line boundary of your site, and your new patio and landscaping are firmly in their sights.
Reason 1: Flood Risk and Drainage
It might not feel like it, but your lawn is a sponge. It absorbs huge amounts of rainwater, preventing it from overwhelming public drains. When you replace that sponge with a non-permeable surface like traditional concrete or porcelain paving slabs, the rainwater has nowhere to go but into the drainage system. Across a whole town, this "urban creep" of paved-over gardens significantly increases flood risk.
Planners are now mandated to combat this. National policy and local plans contain strict rules on Sustainable Drainage Systems (SUDS). If your proposal includes a large area of new hardstanding, the planning officer will ask how you intend to manage the surface water runoff. If you don't have a good answer, they have a valid reason for refusal.
Reason 2: The Biodiversity Net Gain (BNG) Mandate
This is the game-changer. As of April 2024, a new law from the Environment Act 2021 came into force for small developments. It requires nearly all planning applications in England to deliver a Biodiversity Net Gain (BNG) of at least 10%. In simple terms, you must prove that the habitat for wildlife on your site will be in a measurably better state after you've built your extension than it was before.
Here's the problem: a standard lawn, while not a rainforest, has a biodiversity value in the official government metric. A paving slab has a value of zero. Paving a 50 square metre lawn for a new patio creates a huge biodiversity deficit that your project must then overcome. For many projects, this makes achieving the mandatory 10% gain mathematically impossible without a clever landscaping strategy.
Solutions: Turning a Problem into an Opportunity
Instead of seeing this as a barrier, view it as a chance to create a better-designed and more approvable scheme. A landscape plan that embraces sustainability can be the key that unlocks your permission.
Problem | Solution | How it Helps Your Application |
Surface Water Runoff | Permeable Paving: Use materials like gravel, resin-bound gravel, or specific blocks that allow water to soak through into the ground beneath. | Directly addresses SUDS and flood risk policies. Shows the planner you have a sustainable drainage strategy. |
Water Management | Rain Gardens & Soakaways: Design a shallow, planted depression (a rain garden) or an underground crate system (a soakaway) to collect rainwater from roofs and patios. | Provides a clear, effective method for managing surface water on-site, satisfying drainage engineers. |
Biodiversity Loss (BNG) | High-Impact Planting: Use the BNG Small Sites Metric to your advantage. Replacing a 50m² monoculture rye grass lawn with 30m² of native wildflower turf and a 20m² wildlife pond generates a massive increase in biodiversity units, easily offsetting the loss from the extension's footprint. | Turns the BNG requirement from a major hurdle into a clear win. Demonstrates a significant environmental enhancement. |
Loss of Green Space | Integrated Design: Combine smaller areas of hard paving with deep planted borders, climbing plants on walls, and even a green roof on your new extension. | Addresses local plan policies on amenity and green character, showing a balanced approach to development. |
Export to Sheets
By presenting a simple landscaping plan with your extension application—one that specifies permeable paving and new high-value habitats like a wildflower meadow or pond—you are no longer just asking for permission to build. You are presenting a holistic, sustainable development that proactively solves the council's key concerns. This approach transforms your patio from a potential liability into a powerful asset for your planning approval.
Beyond the Red Line: Landscaping for Planning Success
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Disclaimer: This post provides general information for educational purposes only and does not constitute professional planning or legal advice. You should always consult with a qualified planning professional and your local planning authority before starting any project. Planning outcomes are not guaranteed.