Lewisham architects | Residential architect projects

Summary planning and design guide | Lewisham residential architect advice

General principles and good practice

45 degree guide – This test should be used where the proposed development is at right angles to
the affected window of the neighbouring property:

• Draw a line at 45 degrees upwards from the centre of the affected window.
• Draw a line at 45 degrees sideways from the centre of the affected window.

If the proposed development is both higher and wider than these 45 degree lines, there may be an unacceptable loss of daylight to the affected window.

25 degree guide – This test should be used where the proposed development faces the affected window of the neighbouring property:

Draw a line at 25 degrees upwards from the centre of the affected window.

If the proposed development is higher than this 25 degree line, there may be an unacceptable loss of daylight to the affected window.

Scale and form – All extensions and alterations must not be excessive in scale and should be subordinate to the original dwelling and immediate neighbours. Its form should, in general, be consistent with the host property.

High quality design – Innovative, high quality and creative contemporary design solutions are welcomed by the Council, as long as the design carefully considers the architectural language and integrity of the original building and avoids any awkward jarring of building forms.

Respecting the original building and its setting – The architectural character and setting of the original building must be respected. This includes the scale, mass, rhythm, plot size, eaves line and building line of the building and its neighbours. This does not mean that original buildings need to be replicated, however, if this is the proposed approach then the works will need to be carried out to a very high quality like in every other occasion.

Considering neighbours – You should have regard to the fact that a proposed extension or alteration could have an impact on the light, outlook or general amenities of adjoining properties. You should therefore have regard to the size, scale and location of the extension to sensitive parts of adjoining properties such as existing windows in the rear or side elevations. Extensions / alterations should not result in a harmful sense of enclosure or have an overbearing or overly dominant impact on adjoining properties.

Materials – Materials for extensions and alterations can either match the building materials of the original building or be of a contrasting, modern aesthetic. Either way materials should be of the highest quality, be durable and should weather well.

The detail of materials is integral to the scheme as a whole. Quality of materials, samples and detailed, larger scaled plans will be required.

Design principles for rear extensions

Rear extensions should generally not be more than 3m deep for terraced or semidetached properties. Deeper extensions may be acceptable for detached properties or on large plots. Under no circumstances should the extension take up more than half the depth of the original rear garden/yard to avoid the overdevelopment of sites.

The acceptable height on the boundary will depend upon a number of factors specific to its context: including the length of the extension; adjacencies; width of the neighbouring garden etc.

This should also be informed by the daylighting test described above and should avoid being overbearing on neighbouring properties.

However as a general rule, extensions extending up to 3m in length should be no more than 3m in height on the boundary.

Extensions which exceed this length and exceed a height of 2.5m on the boundary are unlikely to be supported.

Where a pitched roof is proposed, the ridge height should be visibly lower than the sill of any first floor windows (minimum of 2 or 3 brick courses)

Extensions should not overlook or have an overbearing or enclosing effect on adjacent properties by way of their height, position or depth.

It is unlikely to be possible to use the roof of your extension as a terrace unless it can be demonstrated that there would be no unacceptable impact to any neighbouring properties’ privacy.

On semi-detached properties extensions should not extend beyond the main side walls of the host building except where an L shape form is proposed.

L-shaped extensions which combine a single storey rear extension and a single storey side extension should not overdominate the original building. It is recommended that a path of at least 1m is maintained to provide access to the rear garden.

Proposals of this nature should adhere to the guidance for both rear extensions and side extensions.

Two storey rear extensions

The extra height and bulk of a two or more storey extension compared to a single storey structure can exacerbate problems of: overlooking; overshadowing; loss of light; and a general sense of enclosure to neighbouring properties. The additional height also gives the extension greater visual prominence.

These can be difficult to achieve in a sensitive manner and will only be considered where the applicant can demonstrate exceptional design quality.

In these cases the onus is on the applicant to demonstrate that the characteristics and integrity of the host property is maintained/enhanced and that the impact on neighbouring properties is not significant.

For these types of application you are advised to seek pre-application advice. Details can be found on the Council’s website.

A single storey extension built on top of a ground floor extension is likely to have the same impact and sensitivities as a two storey rear extension. Again you are advised to seek pre-application advice.

Design principles for single storey side extensions

A single storey side extension should be subordinate to the host property and should not dominate the original house footprint. In cases of exceptional quality design, different options may be considered.

Single storey side extensions must sit comfortably with the original building and respect the proportions of the existing building. In the case of corner properties, side elevations can be read as the principle elevation and the design needs to reflect this.

The extension should not project forward of the front facade and should normally be set back by a minimum of 150 mm – or the distance set by good quality precedent. This helps to make a clear distinction between old and new. In the case of corner properties, the building line may be defined by the side road.

The width of a side extension (in the majority of cases) should be no more than half the frontage width of the original property.

In terms of height, there may be instances where there is sufficient distance between neighbouring properties or the land is sloping so an extension could be taller than its neighbour(s). However the application would have to demonstrate that there is no harm to the neighbouring properties or to the appearance of the house or harm to the significance of either a designated or non designated heritage asset.

The roof form should complement the character of the original building.

Side windows will not normally be permitted unless it can be demonstrated that no overlooking of neighbouring properties would occur and that they do not prejudice the development of adjoining land. Otherwise, they may be acceptable if the windows are high level/ obscured and designed not to be opened.

Design principles for two storey side extensions

The guidance for one storey extensions applies to two storey extensions along with the following.

Not only should two storey side extensions be set back from the front facade, where relevant, the proposed roof of the extension should be set down from the main ridge line.

Side extensions of more than one storey can significantly harm the openness that forms the character of much of the borough.

Two or more storey side extensions should be set in at least 1m from the boundary and set back at least 1m from the front elevation to reduce this harm. Where it is appropriate to build to the boundary, the setback from the front elevation should be at least 2m.

Side extensions should be accessed from the main property and normally should not have an additional front door.

Design principles for single storey infill extensions

The design of the extension should be high quality and should either match or, if a contemporary design approach is taken, should complement the host property. The extension should always remain subordinate to the host property.

Pitched roofs should not wrap around first floor windows and there should be at least the height of 2 to 3 bricks between the highest point of the roof of the extension and any first floor window in the host property.

Single storey infill extensions can, if too high have a detrimental impact on neighbouring amenity, particularly in terms of sense of enclosure, daylight and outlook. Therefore it is important to ensure that the height proposed is justified and causes no or minimum impact.

The height of infill or wrap around extensions will be dependent on the scale of the outrigger, width of the garden and depth of the proposed extension. As a general rule, extensions extending up to 3m in length should be no more than 3m in height, beyond that the height needs to be considerate of the impact of the adjacent property.

Extensions which exceed 3m in length and exceed a height of 2.5m on the boundary are unlikely to be supported. Lower height may be required depending on special circumstances, eg ground level differences.

Design principles for wrap around extension

The design principles for infill extensions set out above also apply to wrap around extensions.

Wrap around extensions should be clearly readable as additions and respect existing building form.

These extensions are generally in excess of 3m in length and therefore the height on the boundary is a key consideration.

The height of infill or wrap around extensions will be dependent on the scale of the outrigger, width of the garden and depth of the proposed extension. As a general rule, extensions extending up to 3m in length should be no more than 3m in height, beyond that the height needs to be considerate of the impact of the adjacent property.

Extensions which exceed 3m in length and exceed a height of 2.5m on the boundary are unlikely to be supported.