Garden-building permitted development rights are not a general permission to create another dwelling. [1]
Start with the whole plot
Draw the existing house, proposed house and the land each would retain. Test the arrangement as two functioning homes: entrances, usable outdoor space, windows, waste storage and access to services. A new house that works only by leaving the original house with unacceptable living conditions does not resolve the planning problem. [2] [3]
The NPPF published on 17 August 2026 supports sensitive additional development within residential plots through policy L2. That support is conditional: street character, safe access, daylight, sunlight, privacy and external amenity remain relevant. The policy also contains specific curtilage-footprint and retained-land tests. It is a planning policy, not a new permitted development right. [2]
Establish the constraints before fixing a design
A useful feasibility exercise has three parts:
- Planning and context: examine the existing permissions, local policies, surrounding buildings and any restrictions affecting the site. A previous approval next door is useful context, not permission for this plot. [1] [3]
- Physical capacity: test floor areas, bedroom occupancy, accessibility and the relationship between windows and boundaries. Allow space for the less visible requirements, including drainage and storage. [3] [4]
- Nature and access: identify trees and possible protected-species habitat, and demonstrate how emergency access and waste collection would work. [5] [6] [7] [8]
Use a measured layout rather than an outline box marked “new house”. Showing furniture, circulation and the retained garden makes the practical consequences easier to assess. This is a useful way to apply the design-led approach in London's housing policies. [3]
Small-site biodiversity rules changed in 2026
For applications made on or after 6 August 2026, sites of 0.2 hectares or less are exempt from statutory Biodiversity Net Gain unless the development would cause a loss of biodiversity value in on-site priority habitat. The separate self-build exemption was removed from that date. Earlier applications have different transitional treatment. [9]
Do not treat the size exemption as permission to clear everything. Tree controls and protected-species requirements are separate, and an ecological assessment may still be necessary where habitat could be affected. [5] [6]
Permission is not the final readiness check
A new dwelling also needs the appropriate building regulations process. Check the council's CIL position before beginning work: self-build relief, where available, requires its own application and procedures. Merely describing the house as “for my family” does not complete them. [10] [11]
For a London site, read the adopted London Plan alongside the borough's requirements. The replacement London Plan and London Small Site Design Code were still drafts when checked on 2 October 2026. Neither should be presented as an adopted guarantee that a garden plot is buildable. [12] [13]