A Winning Design

Design and Appearance

Bearing in mind that each location has its own distinctive character, often at micro as well as macro levels, try and look at your area carefully and decide what it is that makes up its character. For example, what design details make your house and its neighbours individually and collectively distinctive.

It is usual for Urban Character Studies and Village Design Statements to identify key local area characteristics and you may find these in your Local Authority’s Statement of Planning Policy.  This can help you decide whether what you have in mind is likely to be acceptable, or not.  Maybe you can even find some, or all of this information on their website.

Bear in mind that your house extension design needs to be in sympathy with:-

It is a good idea to try and replicate the style and design of your original house in your building extension proposals.  Where possible, make the basic shape of your extension proportional to and subservient gives you the t to the original house.

Although your local planning office are likely to understand that this is not always possible, or appropriate to do this, the size, scale, etc. (depth, width, height) of your extension will be critical in how they determine whether or not your project will be in proportion to the existing building.

Overlarge, disproportionate extensions do not generally find favour with Local Planning Authorities.

Also bear in mind that the roof pitch, style and shape will be a significantly influence an appropriate design. Consider repeating some building features in your extension to help integrate this with the existing structure. However, take care that copying such features does not detract from the original building.

Examples of subservient extensions of a proportionate size

Subserviant extensions of a proportionate size

Rear extensions

Unless in a Conservation Area, or a Listed Building, rear extensions are least likely to have a major impact on neighbours, or the house itself.

If you are intending to extend a terraced or semi–detached property try and follow the pattern of any previous extension/s. In terraced houses, for instance, try and match your proposals to any similar extensions to neighbouring properties, such that they appear to be part of the original design. This can also help to increase privacy and give it to you so it is not all n back gardens.

Sympathetic rear extension

Sympathetic rear extension

Traditional paired outward extension to rear of terraced houses

Traditional terraced paired extension

Extensions with flat roofs seldom seem to blend in with existing dwellings.  They also have a tendency to create long term maintenance issues.  Many local planners seem to prefer pitched roofs, especially if these have the same pitch as the main roof. If this is not possible then this can be an indication that the size of your proposed extension is not in keeping with the scale of the original dwelling. In the main, try and ensure that your two storey extension has a pitched roof.


Avoid flat roofed extensions

Avoid flat roofed extensions


Side extensions

As a general rule, an acceptable side extension will have been designed to be sympathetic and subservient to the main building. Often the appearance can be improved by setting the extension back from the main house. Two storey extensions should not be higher than the existing eaves level.

Sometimes it may be most acceptable to make the extension roof height the same as the existing property.

Set back and lowered - extensions will appear more sympathetic

Set back and lowered extension

With side extensions it is particularly important to make sure that the design takes account of how close any neighbouring property is in relation to the height of the new extension.


Design porches so that they complement the house character

, generally making sure that they are subservient to the original house and avoid the porch visually dominating the street. Porch roofs should reflect the main buildings roof design and pitch. If you porch will be close to your neighbour’s property, design it so that it has least impact on their amenities and appearance of their home..

Choose the materials for your extension so that they match in with the original
building. Not only should their tones and colours match, but also their textures and sizes, e.g. of bricks and roof tiles.

Extensions to older properties may benefit from using carefully selected second-hand materials, especially if their source can be verified as legitimate.

However, there are some exceptional circumstances where the use of different or even contrasting materials may be appropriate. This might be true if their selection could enhance the original building and help the extension to appear subservient.

As the mentioned the Police now provide ‘Secured by Design’ guidance including for doors and windows.  Some manufacturers now also offer doors and windows that conform to these guidelines. Following this guidance may not only help your application, but also result in lower house insurance premiums.  For more information contact the Architectural Liaison Officer in your local Constabulary.  

When designing an extension it is important to consider the following:

Size and Proportion

Overlarge windows may not be seen as appropriate for your extension. Aim to keep these in proportion with the existing building and to keep some continuity between this and your extension.

Extension Size and proportion


Match the style of the windows with those in your existing house

Extension window style

Ratio of Wall to Openings

Make sure that the ‘solid to void ratio’, i.e. the amount of openings to solid walls, reflects the character of your existing building.  Try and avoid large, inappropriate areas of glass or brickwork.

extension ratio of wall to openings


Vertical Rhythm

Give special attention to the arrangement of vertical features along the façade of the extension, particularly if these are regular.

extension vertical rythm

Dormer windows are often feature very prominently and can dominate a building. These could be considered as inappropriate if other properties in the area have plain, simple roofs. Subject to available headroom, using roof-lights could be less obtrusive. Conservation roof-lights are now available which reduce the way these intrude on the roof profile.  

Where it is decided to use dormer windows in the design of your extension, try to keep them a low down on the slope of the roof and minimise their size. Dormers should follow the design of the main roof, with windows matching the general rhythm and style of those in the main building.

As previously noted, it is generally best to avoid flat roofed dormers, although sometimes an unobtrusive flat dormer can be better suited to an historic building.

Take care to avoid dormer windows on the side of an extension interfering with the symmetry of the house, terrace, or pair of semi-detached houses. This could also interfere with a neighbours privacy.

matching extension dormer and window positions

If you can use similar detailing to those in your present house, this is likely to result in a more sympathetic and attractive design for your extension. Consider the following details in particular:


It is often easier to integrate you new extension with the old building if you can replicate the head and cill details of windows and doors. Copying details like brick
arches and lintels, or brick ‘soldier’ courses can greatly improve the quality of the final buildings appearance. Most skilled builders can copy even the most complex details. However, be careful to ensure that such detailing is only used if it is already apparent in the existing building.  Introducing new detailing for an extension if it is not already part of the existing building may seem alien and is best avoided.


replicate opening details in your extension

Roof detail

Aim to replicate the eaves, verge, and ridge detail of the existing building. Such elements can really help create continuity between this and your extension.


Brickwork details

In properties built since the 1940’s the brickwork will probably be laid as ‘stretcher bond’. If not it may not be built with cavity walls.

If you have read the ‘Design and Appearance b) Materials’ section above and chosen bricks to match the original house, you should also consider the bonding so as to match this on the extension as well. It is easy to be disappointed if your new extension seems to look different, texturally and visually, especially when you’ve possibly gone to a great deal of time, trouble and even expense the match the bricks. Most often this ‘mismatch’ is due to using the wrong brick bond.

Likewise take care to use the same type and colour of mortar and thickness of joints.  In this way you can make sure the new brickwork blends in properly with the old brickwork. If it is difficult or impossible to match the bricks and/or brickwork, the use of different materials should be considered.



Soldier courses and quoins (corners) should carry through into a new extension so as to integrate this.  Take care when copying these details to make sure they do not detract from the existing house.




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