1. Check eligibility and the original footprint
Confirm that the property is an eligible house with the relevant rights. This route is unavailable on article 2(3) land, including conservation areas, and on Sites of Special Scientific Interest. Flats and maisonettes do not have these householder rights. [1]
Identify original rear and side walls and any earlier additions. A side-return or wraparound design can fail side-extension limits even though its rear projection is less than 6m or 8m. The submitted proposal must satisfy Class A as a whole. [1]
2. Prepare a precise submission
The required information includes the proposed rear projection, maximum height and eaves height, a plan showing the site and proposed development, and the addresses of adjoining premises. Supply the applicant's contact details and the required fee. Use drawings consistent with the actual building to be constructed; vague dimensions make it harder to establish eligibility. [1]
From 1 April 2026, the statutory fee for larger rear-extension prior approval is £249. That is the application fee, not the cost of drawings, building control or construction. Check any separate submission-platform charge before paying. [3]
3. Allow for neighbour consultation
The council notifies adjoining owners or occupiers and gives them the specified opportunity to respond. If an objection is received, the council assesses the effect on the amenity of adjoining premises. An objection is not an automatic refusal, and a neighbour's informal agreement is not a substitute for the procedure. [1]
Keep the conversation focused on the actual proposal: wall height, projection, roof shape and the position of nearby windows. Do not promise a design change without checking that the plans and application will be updated consistently.
4. Wait for the lawful starting point
Do not start until the council has notified you that prior approval is not required, has granted prior approval, or the applicable 42-day period has expired without a decision. Hounslow's guidance expressly warns that this process is required before starting. [1] [4]
Do not rely on a calendar calculation alone. Confirm the complete application's receipt date and that the proposal genuinely qualifies. The expiry of 42 days does not turn an ineligible development into permitted development. Keep the application, receipt evidence and any decision together. [1]
5. Finish the other approvals and build the submitted scheme
Building regulations, party wall procedures and sewer arrangements still need to be resolved separately. Changes to the built dimensions or roof should be checked against the planning position before implementation. [5] [6] [7]
Draft fee regulations propose a different schedule from 8 December 2026. Use the final made regulations and operative schedule when calculating charges for that period. Annual April indexation is a separate reason to re-check a later application. [8][9]