Larger home extensions: depth limits and neighbour consultation

A single storey rear extension on a semi-detached or terraced house can go 3 metres beyond the original rear wall under ordinary permitted development, or up to 6 metres using the larger home extension scheme. For a detached house the figures are 4 metres and 8 metres. The larger depths are not automatic: you have to notify the council first, it writes to the neighbours either side and behind, and if any of them objects it decides whether to approve the extension on amenity grounds.

Nothing can be built until the council has either told you prior approval is not required, given prior approval, or let 42 days pass without determining the notification. That 42 day period is the part most people misunderstand.

Depths allowed with and without the scheme

The larger depths apply to single storey extensions only. A two storey rear extension is limited to 3 metres regardless, and the larger scheme does not touch it.

Height limits apply either way. The extension cannot exceed 4 metres in height, and where any part of it sits within 2 metres of a boundary of the curtilage, the eaves height is limited to 3 metres. Measure heights from the natural ground level at its lowest point beside the extension, rather than from a patio you laid last summer.

"Original rear wall" means the rear wall of the house as it was built, or as it stood on 1 July 1948 if it is older than that. If a previous owner added a 2 metre extension in 1995, you have 1 metre of ordinary allowance left and 4 metres under the scheme, not 3 and 6. This is the single most common reason people find they need a planning application after all.

The 50 per cent rule also still applies. Buildings other than the original house, including the extension and any outbuildings, cannot cover more than half the area of the curtilage. Outbuildings count towards that total, including the ones you may not think of as buildings, which is where the questions about outbuildings with a shower room or kitchenette overlap with the extension calculation.

How the consultation works

You send the council a written description of the proposed development, stating how far it extends beyond the original rear wall, its maximum height and the height of its eaves, together with a plan of the site showing the proposed development, the addresses of the adjoining premises, and your own contact address and email. A fee is payable, set nationally and indexed each April, so take the figure from the current schedule.

The council then writes to the owner or occupier of each adjoining premises, describing the proposal and giving them 21 days to object.

Adjoining premises means premises sharing a boundary with yours. For a mid-terrace that is the two houses either side and anything directly behind. Someone across the road is not consulted, and nor is a neighbour two doors down, however strongly they feel.

If nobody objects within the 21 days, the council must tell you that prior approval is not required and you can build. No judgement, no discretion, no planning balance.

What a neighbour objection triggers

If any adjoining neighbour objects, the council has to consider the impact of the proposed extension on the amenity of all adjoining premises and decide whether to grant prior approval.

The assessment is narrow. It is about amenity, which in practice means loss of light, overshadowing, overbearing effect and loss of privacy to the adjoining properties. It is not an opportunity to reopen design, materials, parking, drainage, boundary disputes or the applicant's character. Objections about those matters should carry no weight, and if the decision notice relies on them that is a ground of appeal.

Councils can and do refuse prior approval. The usual reason is a 6 metre extension running along a shared boundary next to a neighbour's kitchen or living room window, where the effect on light is real. The usual fix is to reduce the depth along the boundary and keep the full depth away from it, or to pull the extension in from the boundary with a side passage.

Overlooking from new windows is handled separately, usually by obscure glazing and restricted opening, and the way those requirements get written down is covered in obscure glazing conditions on side-facing windows.

The 42 day period and its effect

Development must not begin before 42 days have passed from the date the council received your notification, unless it has already told you its decision.

So three endings are possible.

1. The council notifies you within the period that prior approval is not required, because no neighbour objected. You can build immediately.
2. The council notifies you within the period that prior approval is granted. You can build, in accordance with the details you supplied.
3. The 42 days expire with no determination. You can build, in accordance with the details supplied.

The third route is real and it is worth knowing about, but do not rely on it loosely. It depends on the notification having been complete and valid when the council received it, and on you building exactly what you described. A notification missing the adjoining addresses or the eaves height may never have started the clock.

Diary the 42nd day when you submit, and ask the council in writing to confirm the date it received the notification.

Evidence to include with the notification

The regulations ask for a limited set of information, and giving the council slightly more than the minimum reduces the chance of being asked for it later.

Provide a site plan at a recognisable scale showing the house, the extension outline, the curtilage boundary and the adjoining properties. Add a simple floor plan and two elevations with the depth, overall height and eaves height dimensioned. State the construction date of the original house and list any previous rear extensions with their depths, because the original rear wall question will come up. Name every adjoining property with its full address, including flats where a neighbouring building is divided. Describe the external materials, which must be similar in appearance to the existing house.

A short covering note explaining the relationship to the neighbours' windows, with a photograph from each boundary, is not required and frequently helps.

Illustrative example, not a real case: a 1930s semi whose kitchen was extended 2.1 metres in 2004 wants a 6 metre deep single storey extension. Because the 2004 work came off the allowance, the new extension can only reach 6 metres in total from the original rear wall, meaning 3.9 metres of new build. The eaves along the shared boundary are set at 2.9 metres with a mono-pitch falling away from the neighbour, the full depth is held 1 metre off that boundary, and the neighbour does not object. Prior approval is not required and the work starts in week four.

Where the right does not apply

The larger home extension scheme is not available on designated land, which covers conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites, nor on a site of special scientific interest. On a listed building, listed building consent is needed for the works in any event.

It also does not apply to flats and maisonettes, because Class A covers houses only. And it is unavailable where permitted development rights have been removed, either by an Article 4 direction over an area or, very commonly, by a condition on the original planning permission for a newer estate. Check the permission for your house before you do anything else.

Houses created by converting another use under certain change of use classes also have restricted Part 1 rights, so a former office or barn converted to a dwelling may not have the right at all.

Other alterations have their own separate Classes with their own limits, so a scheme combining a rear extension with a loft conversion needs each element checked against its own rules, as with rear dormers on a semi-detached house. And in a conservation area, works you might think of as minor are treated differently, which the discussion of removing a chimney stack in a conservation area illustrates.

Records to keep afterwards

Keep the notification, the plans you submitted, the council's written response or the evidence of the 42 days expiring, dated photographs of the completed work, and the building regulations completion certificate. Put them with the deeds.

A buyer's solicitor will ask, and a prior approval notice is the document that answers them. If you want something stronger, a lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful, and it is worth the fee where the original rear wall calculation was tight.

Building regulations approval is a separate process from all of this, and so is the Party Wall etc. Act 1996 procedure where you build up to or astride a boundary. Neither is covered by prior approval.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. If you would like help preparing the supporting documents, a design and access statement is one of the 66 report types PlanScope can draft.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.