Side Extensions

Policy EM1 - Extensions and Alterations Policy

Many homes within Welwyn Garden City have been designed to carefully balance the architectural appearance of individual properties where side extensions can disrupt or unbalance these carefully considered elevations.  The appearance of the wider street frontage includes a formal planned layout with deliberate gaps between both terrace and detached properties offering generous open spaces with views through to trees beyond, providing a verdant and sylvan setting. Inappropriate side extensions at first floor have the potential to disrupt this rhythm and important visual appearance of the street, having a detrimental impact on the overall values and amenities of the property and the street scene.

In order to retain these core principles it is important to keep appropriate distances between neighbouring homes to retain this open feel, rhythm and character of the street scene while maintaining the amenities and values of the property and the area.

A side extension is to be deemed acceptable if it meets the following principles.

• Design and detailing of side extensions should be consistent with the character of the original property. Materials, scale, proportions and detailing, including fenestration should be mirrored from the existing property within the proposed extension.
• Design of the side extension must be subservient to and in proportion with the existing house and plot. This can be achieved through the allowance for a building set back and a reduced ridge height.
• Varying footprints between ground floor and first floor extensions can create poorly designed proportions and imbalanced buildings and should be avoided unless it can be demonstrated that it would not have any detrimental impact on the character of the existing property or its surrounding context.
• Side extensions to an end of terraced dwelling are not permitted unless it can be demonstrated that the extension would enhance and respond to the group value of the properties within the terrace and its overall context.
• The extension should not cause loss of day/sun/skylight or be unduly dominant from adjoining properties as a result of the size and location of the extension.
• Window positions must not result in a loss of privacy to neighbouring properties
• Crowned roofs must be avoided. Typically crown roof structures are not supported as they do not reflect the original style of a Garden City property and often indicate an extension that is too large.
• Proposed structures, including roofs or gutters, should not overhang property boundaries. Should works extend beyond the property’s boundary, a separate EMS application will be required to be submitted from the owner of the neighbouring property. Applications can only be submitted for the land owned by the applicant.

Ground Floor Extension (Single Storey)

Ground floor side extensions must be designed to accommodate a flat roof system unless individual circumstances indicate otherwise. Parapet roof detailing is deemed acceptable. 

Building heights should be designed in line with Building Regulation guidance.

Any roof lights or lanterns must not be visible from a public vantage point.

Roof lights and lanterns on side extensions at ground levels should not be visible from public vantage points.  A parapet wall can be proposed to obscure these, however their height should be kept to a minimum and not exceed that required by Building Regulations.

Ground floor side extensions to bungalows will only be acceptable where the scale and proportion is sympathetic to the existing dwelling.

Two Storey Side Extensions

Two storey side extensions require greater levels of sensitivity to take into regard the proximity of neighbouring properties. All applications should demonstrate how any likely impact on neighbouring properties is minimised including loss of day/sun/sky light.

To ensure that detached and semi-detached dwellings retain open and detached character; a two storey extension must maintain sufficient space around the dwelling and should reflect the spacing in the street scene.

Two storey side extensions should be designed to appear subordinate to the original property by being set back from the front elevation and with a reduced ridge height, unless the design of the property indicates otherwise.

Upper floor roof pitches should be consistent with the original design of the property where the extended roof is designed to merge with the existing roof structure. Typically crown roof structures are not supported as they do not reflect the original style of a Garden City property and often indicate an extension that is too large. However these could be considered should strong justification be provided in where it can be demonstrated that impact on the character and value of the property would be limited.