Establish what is being created
Draw each proposed dwelling as a complete home, with its own living, cooking, sleeping and sanitary accommodation. Show the shared entrance and circulation separately. A self-contained flat conversion is not the same planning proposal as letting bedrooms with shared facilities as an HMO. [3] [4]
Confirm the existing lawful arrangement before designing the change. A building already divided into flats may need a different application from a single house being divided for the first time; changing the number of dwellings also has building-regulations implications. [1] [5]
Test the council's policy before fixing the number
Some borough policies protect larger family homes or require a family-sized dwelling to remain. Brent's policy BH11, for example, includes floorspace, retained family accommodation and public-transport criteria. A conversion permitted elsewhere is not evidence that the same layout meets the policy for this address. [2]
In London, also assess the homes against London Plan housing-quality policy. Total floor area is only one part of that exercise: privacy, daylight, outlook, storage and outdoor space can affect whether a subdivision works. [3]
For an initial feasibility exercise, compare at least two sensible layouts rather than treating the highest flat count as the starting requirement. Identify the policy constraint that limits each option, so any further survey or design work addresses a specific problem.
Reserve space for the technical design
Creating flats is a material change of use under the Building Regulations. Fire separation and escape need a coordinated design, and separating walls and floors need appropriate sound insulation. These requirements can affect the layout and construction build-ups. [5] [6] [7]
Do not use the full surveyed area as saleable flat area. Measure each dwelling using the relevant space-standard method, then show the common parts separately. Retain enough detail to reconcile the planning accommodation schedule with the technical plans. [8]
Check the proposed electricity and water arrangements early. Existing capacity, the number of meters and the physical supply arrangement are related but different questions. [9] [10]
The 2026 energy and ventilation changes commence for relevant non-higher-risk building work on 24 March 2027, subject to transitional arrangements. A conversion must use the provisions for existing dwellings and material changes of use; the new-build Future Homes Standard is not applied wholesale to it. Higher-risk building work has separate commencement arrangements. [15]
Check environmental requirements without assuming an exemption
From 6 August 2026, the BNG exemption for sites of 0.2 hectares or less uses the area inside the application's red-line boundary. It does not apply where the development impacts on-site priority habitat. The separate self-build exemption was removed for new applications from that date. [11]
A small conversion may therefore qualify for an exemption, but the application should identify the actual basis rather than claim that all conversions are exempt. [11]
Keep the permission and delivery decisions separate
Planning permission settles the proposed development, not the new leases, service arrangements or every construction detail. Plan for building-control approval and, where flats will be sold separately, legal documents and accurate title plans. [12] [13]
The draft replacement London Plan is not yet the adopted plan. Review any relevant emerging policies during the application, without presenting consultation proposals as settled requirements. [14]