Extending the Outrigger: The 3-Metre Back-Addition Extension That Needs No Planning Application, What It Gives a Terrace and What It Costs
By Anderson & the LCCL Construction Team | Finchley N3
Walk down any Victorian street in London and look at the backs of the houses: a main block two rooms deep, and behind it a narrower two-storey wing — the outrigger, or back addition — that holds the kitchen on the ground floor and the bathroom above, with a strip of side return beside it. Most of the extension conversation on these houses is about the side return. This piece is about the other move: extending the outrigger itself straight back into the garden, which the permitted development rules allow up to 3 metres with no application at all.
As LABC Building Excellence Award Winners 2024 for Best Residential Extension in London — and London Regional Winner 2026 for Best Conversion or Alteration to an Existing Home — we build extensions on terraces of this kind across London and Hertfordshire, and the outrigger extension is the smallest extension on our price list — from £36,000 inc. VAT for 8 to 18 square metres — which makes it a sensible first move for a family that needs a dining space more than it needs a new kitchen.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — about two minutes, free, and the from-price for each part that qualifies appears on screen and in your inbox.
The rule: the outrigger's rear wall is an original rear wall
Permitted development measures a rear extension from the original rear wall of the house. A house with an outrigger has two: the rear wall of the main block, and the rear wall of the outrigger. The rules apply to each, so the outrigger can be extended by up to 3 metres beyond its own rear wall (4 metres on a detached house), provided the extension stays within the outrigger's width, is single storey, no higher than 4 metres with eaves no higher than 3 metres within 2 metres of a boundary, in materials of similar appearance, and the house and all its extensions together cover no more than half the garden. The outrigger must be original — part of the house as first built — which on a Victorian terrace it almost always is; an outrigger added later is itself an extension and the 3 metres is measured from the wall behind it.
Where every condition holds, the extension is permitted development and we apply for a Lawful Development Certificate (£274, up to eight weeks) so the council confirms the position in writing. The 6-metre larger-home route also applies to the outrigger's rear wall, through prior approval, but in most London boroughs the 3-metre version is the one worth having: no neighbour consultation, no refusal risk, and a garden left behind it. Our Planning check reads the conservation-area and Article 4 data for your postcode before it gives an answer; the council has the final say on any application.
What 3 metres on the outrigger gives you
An outrigger is usually 2.5 to 4 metres wide, so 3 metres of depth is 8 to 12 square metres on most terraces, up to 18 on the wider Edwardian houses: a dining area at the end of the kitchen with doors to the garden, or a utility and a downstairs WC the house never had, or the kitchen moved to the end so the old kitchen becomes the dining room. It does not give the full-width room — that needs the side return filled in as well — but it gives the length, and on a terrace where the side return is already used for the kitchen it is the simplest way to add floor at the back without a planning application.
Combining it with the side return
The outrigger extension is often built together with a side-return infill under one contract: 25 to 40 square metres across the full width of the back of the house, from £72,000 inc. VAT. The infill has its own rules. It must be single storey, under 4 metres high and no wider than half the width of the original house, and because it also projects beyond the rear wall of the main part of the house, the rear-depth limit applies to it as well: up to 3 metres from that wall with no application, 3 to 6 metres through prior approval and its neighbour consultation. Joined to the outrigger extension as a single L-shape, the two become a wraparound, which is a householder planning application. Which route your house takes depends on the length of the side return and where the house is, and we set it out after the survey.
The first-floor option
Many families extend the outrigger on both floors — a bigger bathroom or a fourth bedroom above the new dining space. That is a two-storey rear extension in planning terms, and it is permitted development only where it stays within 3 metres of the original rear wall, keeps at least 7 metres between its rear wall and the rear boundary, stays 2 metres from the side boundaries and sits below the main ridge; on most London terraces the 7-metre rule or the 2-metre rule fails, so the first floor is usually a householder planning application, and in a conservation area it always is. A first-floor extension over the outrigger starts from £54,000 inc. VAT (£45,000 + VAT), 12 to 22 square metres.
Building control and the party wall
Building regulations apply whatever the planning route. The inspector sees the foundations — which on an outrigger extension run along the neighbour's boundary and on London clay with street trees are often deeper than the standard metre — the steel across the old rear wall of the outrigger, the damp-proofing, insulation, drainage and glazing, and the finished extension before the completion certificate. The excavation beside the boundary and the steel on the party wall bring the Party Wall Act in, so a notice goes to the neighbour; our structural engineer produces the calculations and the drawings go to building control before anything is dug.
What an outrigger extension costs
Rear extension to the outrigger: from £36,000 inc. VAT (£30,000 + VAT), 8–18 m², six to ten weeks on site.
Side-return infill: from £42,000 inc. VAT (£35,000 + VAT), 12–20 m², eight to twelve weeks on site.
Side return + outrigger extension together: from £72,000 inc. VAT (£60,000 + VAT), 25–40 m², twelve to sixteen weeks on site.
First-floor extension over the outrigger: from £54,000 inc. VAT (£45,000 + VAT), 12–22 m², planning application on most terraces.
Every figure is design and build at economy specification, shell-and-plaster finish, and includes the survey, the drawings, the structural calculations, building control and a 12-month workmanship guarantee, with a 10-year LABC structural warranty on every project. The final price is fixed in writing after the survey and is postcode dependent. The knock-through into the existing kitchen is priced as its own line.
Anderson's advice
Check what the outrigger is before you draw on it. On some terraces what looks like the original outrigger is a later rebuild or a lean-to that was squared off, and the 3 metres is then measured from a wall further forward than the one you can see. Our team confirms at the survey that the back addition is original, from the planning history and from the building itself, before the drawings start. It is a short check, and it saves a certificate being refused on a point of history.
What our clients say
“Hired LCCL Construction to design and build us a rear house extension. Found them easy to work with and are pleased with the results. They have been recommended to us for the whole build including designs and construction. The rear extension feels amazing, it is spacious and bright, the project finished on expected budget and within the timeframes agreed.”
— James Grimsdale, Google Reviews
Frequently asked questions
Can I extend the outrigger of a terraced house without planning permission?
Usually, yes. The outrigger's rear wall counts as an original rear wall, so a single-storey extension of up to 3 metres beyond it, within the outrigger's width, under 4 metres high and in similar materials, is permitted development on a house outside a conservation area. We confirm it with a Lawful Development Certificate; the council has the final say.
How much does an outrigger extension cost in London?
From £36,000 inc. VAT (£30,000 + VAT) for 8 to 18 square metres, design and build at economy specification with the survey, drawings, structural calculations and building control included. Combined with a side-return infill under one contract, from £72,000 inc. VAT. The final figure is fixed in writing after the survey.
Can I extend the outrigger on both floors?
Only within tight limits under permitted development — 3 metres deep, 7 metres from the rear boundary, 2 metres from the side boundaries — which most London terraces cannot meet, so a first-floor extension over the outrigger is normally a householder planning application. Outside conservation areas it is approved more often than refused; we prepare and submit it.
Check your own house
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — about two minutes, free, and the from-price for each part that qualifies appears on screen and in your inbox.
To talk through an outrigger extension on your terrace, book a free 30-minute consultation call with LCCL Construction on 020 8037 7332, or get an instant estimate in about two minutes. The rear-extension rules in full, including the 6-metre route, are in rear extensions under permitted development in London.
One team, one contract, one point of contact — from first sketch to handover.
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