Small sites policy and what it supports in outer London

London small sites policy sits in policy H2 of the London Plan 2021, which defines small sites as those below 0.25 hectares and asks boroughs to support well-designed new homes on them. The policy goes further than general encouragement. It asks boroughs to apply a presumption in favour of certain categories of small housing development, which include infill on small vacant and underused sites, incremental intensification of existing residential areas within reasonable reach of a station or town centre, small-scale redevelopment of existing housing, residential conversions and extensions, and new mews and courtyard forms.

For an investor working on one or two plots at a time, the practical value is that you are not arguing from a standing start. You are arguing within a category the plan already supports.

What counts as a small site

The 0.25 hectare threshold is the definition. Below it you are in policy H2 territory. Above it you are not, whatever the unit count.

That matters because a site of 0.3 hectares delivering six houses is not a small site under the policy, while a site of 0.2 hectares delivering fifteen flats is. Measure the red line area before you decide which policy framework you are working in, and measure it properly rather than estimating from a title plan.

Separately, the major development threshold of ten or more dwellings governs the affordable housing and other requirements, and those two thresholds do not line up. A small site can be a major application.

The presumption and what it is worth

Policy H2 asks boroughs to apply a presumption in favour of the listed categories, and to resist refusing those schemes on local character or density grounds where the design criteria are met.

The categories to check your site against are infill on small vacant or underused land, small-scale redevelopment of existing housing, conversions and extensions creating additional homes, incremental intensification of existing residential areas within reasonable reach of a station or town centre boundary, small sites within or adjacent to town centres, and new mews or courtyard development.

The presumption is a policy presumption, not a legal one. It shifts the burden of argument rather than guaranteeing an outcome, and it is conditional on the design criteria in the policy being satisfied. A scheme that fails on daylight to neighbours, on amenity space or on refuse and cycle storage does not get the benefit of it.

What it does do is answer the single most common objection to a backland or infill scheme, which is that it is out of character with the area. Policy H2 anticipates that objection and asks boroughs not to rely on it where design quality is there.

Infill, backland and corner plots

These are the three forms that come up most.

Infill on a gap site is the simplest case. The usual constraints are the building line, the relationship to flank walls, overlooking and the distance to the rear boundary.

Backland development behind existing houses is harder because access runs past habitable rooms and the plot is often enclosed on three sides. The things that decide it are the access width and surface, the noise and disturbance from vehicle movements past bedroom windows, daylight to the host dwellings and to the new units, and whether the new homes get adequate private outdoor space. Policy D6 of the London Plan sets a minimum of 5 m² of private outdoor space for a one or two person dwelling, with an additional square metre for each further occupant.

But corner plots are often the best opportunity in outer London, because a wide corner garden can take a new dwelling fronting the side street without the backland access problem. Watch the highway visibility splay, any existing street trees, and whether the corner contributes to a recognisable townscape feature.

Intensification of existing housing

The intensification limb is the one most relevant to investors with existing stock. It covers adding homes to an existing residential plot or building rather than developing new land.

Routes include subdividing a large house into flats, adding a storey, converting a roof space with the addition of a mansard, building in a side or rear garden, and replacing a single dwelling with a pair or a small block.

Two cautions. First, an Article 4 direction may have removed the permitted development rights you were relying on, including rights to change between a dwellinghouse and a small house in multiple occupation. Check the direction and what it withdraws. Our note on Article 4 directions in London covers the office-to-residential equivalent, and the checking method is the same.

Second, the upwards extension rights in the General Permitted Development Order 2015 are separate from policy H2 and come with their own conditions and prior approval matters. Where the right applies, prior approval is a different and usually faster process than a full application, and it is worth testing before assuming a planning application is needed.

Design quality expectations

The presumption is conditional, so the design evidence carries the application. Four areas decide most small site schemes in outer London.

The daylight question is where small schemes most often fail, and the comparative targets in the guidance matter more in dense London than the absolute ones, a point our note on BRE 209 in dense London develops. A daylight and sunlight assessment covering both the neighbours and the proposed units is the document that answers it.

Where boroughs resist

Policy H2 does not override everything, and four lines of resistance remain legitimate.

Conservation area and listed building constraints are unaffected. Where the site sits in a conservation area, the design conversation is about character in the statutory sense rather than about general local character, and the presumption does not displace it.

Garden land is contested. Residential gardens are not previously developed land in national policy terms, and some boroughs have policies resisting garden development. Policy H2's intensification limb supports some of it, so this is where the policy conflict usually sits.

Parking and highway safety. Outer London boroughs with low public transport accessibility often resist car-free development, and a scheme with no parking in a street with heavy parking stress will attract objections. A parking stress survey is the evidence that settles it.

Trees. A mature tree in the middle of a backland plot, protected or not, can end a scheme. Get an arboricultural assessment before you draw the layout rather than after.

Making the policy case

Write the application so the reader can place it in the policy framework in the first paragraph.

Say the site area in hectares and state that it is a small site under policy H2. Name the category the scheme falls into, using the policy's own language. Then work through the design criteria one at a time, with the evidence attached to each.

Deal with character explicitly rather than hoping nobody raises it. Set out what the prevailing pattern is, how the scheme responds to it, and where it deliberately differs. The design-led approach to capacity in policy D3 is the companion argument, as our note on optimising site capacity sets out.

A planning statement structured that way does the work, and PlanScope can produce an AI-assisted draft of one structured to UK planning policy with the site-specific facts flagged for completion.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.