Permitted Development Checklist for London House Extensions: The Complete Rules Before You Build

**The basic PD rule for single-storey rear extensions**:

A single-storey rear extension can be built under permitted development (without planning permission) in England if it meets ALL of the following criteria:

*1. Maximum rear projection — measured from the original rear wall of the dwellinghouse*:

• •Detached house: the extension must not project more than **4 metres** from the original rear wall of the dwellinghouse
• •Attached house (terraced or semi-detached): the extension must not project more than **3 metres** from the original rear wall of the dwellinghouse

IMPORTANT: the projection is measured from the original rear wall of the house — meaning the wall of the house as originally built, not the wall of any previous extension. If the house has already had a previous extension added to the rear, the projection of the new extension is measured from the original house wall (not the back of the previous extension). A previous extension that already projects 2m cannot be extended by a further 1m (to 3m total) and claimed as PD — it must be assessed as 3m from the original wall.

*2. Maximum height — eaves and ridge*:

• •Maximum eaves height: **3 metres** (the eaves are the point where the roof slope meets the external wall; this is typically where the gutter sits)
• •Maximum overall height: **4 metres** (for a dual-pitch roof — pitched roof with two slopes); **3 metres** for a flat roof or a single-pitch roof (lean-to)

For a standard flat-roof single-storey rear extension (the most common extension type in London): the overall height must not exceed 3 metres (flat roof = same height as eaves = same as ridge). Most London extensions are built at 2.8–3.0m internal ceiling height, which with the flat roof structure and waterproof membrane typically puts the overall external height at just under 3m.

*3. The extension must not be nearer the highway than the original house*:

The extension cannot extend forward of the principal elevation or any side elevation that faces a highway. For a rear extension in a standard terrace (where the rear garden does not abut a highway), this is not typically a constraint. However, in corner plots or through-terrace properties, the rear may face a highway and this rule can restrict the extension.

*4. The extension must not cover more than half the curtilage (garden area)*:

The combined area of all outbuildings, extensions, and additions (not including the original house) must not exceed 50% of the total curtilage (the total area of the land around the house, excluding the original footprint of the house). For most London Victorian terraces with small rear gardens (15m–25m long), a modest rear extension is unlikely to trigger this limit — but for small curtilage properties (maisonette with a very small garden; corner house with limited garden area), this calculation should be checked.

*5. No side elevation windows*:

If the extension has an upper-level floor (not applicable for single-storey), the side elevation windows must be obscure-glazed and fixed shut (or top-hung with an opening of not more than 1.75m above the internal floor level). For single-storey rear extensions, there is no restriction on side-elevation windows under PD.

*6. The extension must use similar materials to the existing house*:

• The extension must use materials of a similar appearance to those used in the construction of the exterior of the original dwellinghouse. In practice, this means:
• •For a brick-built London Victorian terrace: the extension walls should be in London stock brick or a brick of similar colour, size, and texture
• •For a rendered property: the extension should be rendered to match
• •For a stone-built property: the extension should use matching stone or an approved alternative

Building Control will check that the specified materials are appropriate; in a conservation area, the local planning authority (not Building Control) makes this assessment.

**The Larger Home Extension prior approval — extending to 6m and 8m**:

• For larger rear extensions exceeding the standard PD limits (3m for terraced/semi; 4m for detached), a 'Prior Approval for a Larger Home Extension' can allow:
• •Detached houses: up to **8 metres** rear projection (single-storey only)
• •Semi-detached and terraced houses: up to **6 metres** rear projection (single-storey only)

• To use the Larger Home Extension prior approval route:
• •The extension must be single-storey only (max height rules still apply)
• •An application for prior approval must be submitted to the LPA (fee: £258)
• •The LPA must consult adjoining neighbours for 21 days
• •If no neighbour objects, or if the LPA determines that the impact on neighbours is acceptable, the prior approval is granted
• •If a neighbour objects, the LPA assesses the impact on amenity — the extension can still be granted but the LPA must make this assessment

The Larger Home Extension route is very useful for London terraced houses where a large rear extension is needed but the 3m standard PD limit is insufficient — it allows up to 6m (for terraced/semi) without a full planning application, subject to the neighbour consultation.

**Two-storey rear extensions under permitted development**:

A two-storey rear extension (or any extension involving more than one storey) has MORE RESTRICTIVE permitted development limits than a single-storey extension:

• •Maximum rear projection: **3 metres** from the original rear wall (the same as a single-storey terraced/semi extension — irrespective of whether the house is detached)
• •The extension must be within 7 metres of the rear boundary
• •Maximum height: must not exceed the height of the existing house roof
• •The roof pitch must match the existing house (you cannot use a flat roof for a two-storey extension)
• •Side-facing windows above ground floor: must be obscure-glazed and non-opening (except for top-hung opening lights above 1.75m)

For London Victorian terraces where the rear garden may be only 8–12m long, the '7 metres from the rear boundary' rule can be a significant constraint on a two-storey rear extension. If the garden is 10m long and the existing house projects to 6m from the rear boundary (as original), only a 1m-deep two-storey extension can be built within 7m of the rear boundary (6m house + 1m extension = 7m). This often means that a two-storey extension in a short-garden London terrace requires a planning application.

**Loft conversions under permitted development**:

Loft conversions in dwellinghouses (converting the existing roof space) can be carried out under permitted development if ALL of the following conditions are met:

• *Volume limits (total cubic metres of additional roof space)*:
• •Detached and semi-detached houses: up to **50 cubic metres** of additional roof space
• •Terraced houses: up to **40 cubic metres** of additional roof space

These volumes include ALL roof space additions — dormers, roof windows, and any alterations to the roof structure. A single dormer window on a standard London Victorian terraced house typically uses approximately 15–25 cubic metres of volume allowance, depending on its width and depth. A full-width rear dormer on a standard terrace typically uses 35–50+ cubic metres — which may exhaust the 40 cubic metres allowance for a terrace in a single dormer.

• *Position requirements*:
• •No extension to the roof space can exceed the height of the existing roof ridge
• •Dormers must be set back at least 20cm from the eaves on any elevation that faces a road
• •No verandah, balcony, or raised platform
• •Side-facing windows must be obscure-glazed and non-opening (except top-hung opening lights above 1.75m from the internal floor)
• •Any side-facing dormer must be set in from the main roof slope (not extend beyond the edge of the roof)

*Conservation areas and Article 4 directions*: In a conservation area, permitted development rights for roof additions (including dormers) are typically removed by Article 4 direction. In most London conservation areas — and conservation areas cover huge areas of inner London — a dormer requires a full planning permission application, regardless of the PD volume allowance. Always check conservation area status before assuming PD applies.

**Outbuildings and garden structures under permitted development**:

• Detached outbuildings (sheds, garden rooms, studios, garages) can be built under PD if:
• •The total combined floor area of all outbuildings does not exceed 50% of the total curtilage (combined with extensions)
• •The outbuilding is not in front of the principal elevation
• •Maximum height: 2.5m (flat/mono-pitch roof) within 2m of the boundary; 4m (dual-pitch) or 3m (any other roof) elsewhere
• •The outbuilding is used for a purpose incidental to the enjoyment of the dwellinghouse — not as a separate dwelling or for business use
• •For buildings within 2m of the rear or side boundary: maximum 2.5m height (flat or mono-pitch)

For a garden room/home office, PD rules apply — but if it is to be used as a self-contained unit with sleeping accommodation, kitchen, or bathroom, it may be treated as a separate dwelling and require planning permission regardless of size.

**Porches under permitted development**:

• A porch at the front of a dwellinghouse can be added under PD if:
• •The porch does not exceed **3 square metres** in ground area (measured externally)
• •The maximum height is **3 metres**
• •The porch is not within 2m of the boundary with a highway

For small London Victorian terrace porches, these limits are sufficient for most typical front porch additions. However, in conservation areas, porches are typically not PD and require planning permission — the original front elevation character is generally protected by Article 4 direction.

**1. Conservation areas**:

• In conservation areas, Article 4 Directions are frequently made by the London Borough to remove certain classes of permitted development rights — particularly those affecting the external appearance of buildings. The permitted development rights typically restricted or removed in London conservation areas include:
• •Roof additions (dormers, roof windows visible from the street)
• •Extensions to the principal elevation
• •Changes to windows and doors (replacing sash windows with casements)
• •External cladding or rendering
• •Solar panels on certain roof slopes
• •Hard surfacing (front garden driveways)

Conservation areas cover a substantial proportion of inner London — including virtually all of Camden, Islington, Kensington, Chelsea, Westminster, Wandsworth, Hammersmith, and large parts of Lambeth, Southwark, Tower Hamlets, and Hackney. ALWAYS check whether the property is in a conservation area before assuming PD rights apply.

To check: search the London Borough's planning map (most London Boroughs have an interactive GIS map on their planning website) or contact the planning department directly.

**2. Listed buildings**:

Listed buildings have no permitted development rights for works that would affect the character of the building. Almost all external and internal structural works require listed building consent as well as planning permission. London has a very large number of listed buildings — particularly in central and inner London.

**3. Article 4 Directions (beyond conservation areas)**:

In addition to conservation area Article 4 directions, individual Article 4 Directions can be made for specific streets or areas that are not in a conservation area but have planning authority-specific heritage or character concerns. Some London streets not in a formal conservation area are subject to Article 4 Directions. Check with the specific London Borough if the situation is not clear.

**4. Flats and maisonettes**:

The PD rights discussed in this guide apply only to dwellinghouses — freehold or leasehold houses. Flats, maisonettes, and apartments do NOT have the same permitted development rights. Works to a flat typically require a full planning application. Additionally, the lease of a flat may restrict alterations — even where planning permission is not needed, the freeholder's consent may be required.

**5. Properties with previous planning conditions restricting PD**:

• Some properties have planning conditions attached to a previous planning permission that explicitly remove permitted development rights from that property. This can occur when:
• •A previous developer obtained planning permission with a condition requiring future works to obtain planning permission
• •A previous householder application for a controversial extension was approved with a condition restricting further PD extensions
• •The property is in an area where the LPA routinely removes PD rights through planning conditions

Always check the planning history of the property (available on the London Borough's planning portal by searching the address) to see whether any conditions restrict PD.

**6. Properties where original PD volume has been used**:

For loft conversions, the 40 cubic metres (terraced) or 50 cubic metres (detached/semi) volume allowance is cumulative across the history of the property — a previous dormer conversion reduces the allowance for any further roof additions. If the property has had a previous dormer that used 30 cubic metres of the 40 cubic metre allowance, only 10 cubic metres remains for further additions.

The original PD allowance can also be reduced or eliminated if a previous extension was approved under planning permission (rather than PD) — the planning permission application may have a condition removing further PD rights for roof additions.

**Practical steps before building under PD**:

1. Confirm the property is a dwellinghouse (not a flat) 2. Check the LPA planning map for conservation area status 3. Search the planning history on the LPA's website for any Article 4 directions or restrictive conditions 4. Measure the proposed extension and confirm it meets ALL PD criteria (projection, height, materials, curtilage cover) 5. Consider obtaining a Lawful Development Certificate (LDC, £129, 8-week LPA determination) — provides formal written confirmation from the LPA that the works are PD. Strongly recommended for extensions close to the PD limits or for properties being sold within the next 3–5 years