A home extension is one of the most significant investments a homeowner in Kent or South London can make. Done well, it adds space that genuinely becomes part of the fabric of the house: a room people use every day and cannot imagine being without. Done without adequate design attention, it adds floor area that never quite becomes a room. Awkward proportions, poor light, a sense that the new space sits apart from the rest of the house rather than belonging to it.
The difference, consistently, is the degree to which interior design was considered from the beginning. An extension is not simply a construction project with a room inside it. It is an opportunity to create one of the most used and loved spaces in the home, and that opportunity is most fully realised when a designer is involved before the structural decisions are made.
This guide covers how BD Interiors approaches extension projects for clients across Kent, South London, and Surrey, and what the key decisions are that determine whether an extension adds lasting value to the life of a home.
Involve the Designer Before the Builder
The most consistent mistake in extension projects is treating interior design as something that happens once the structure is complete. In practice, many of the decisions that define the quality of the finished space are structural. The direction and size of glazing determines where natural light falls and at what times of day. The position of the internal opening between extension and existing house determines how the spaces connect and whether the flow feels natural. The height of the ceiling determines what is spatially possible.
A designer involved before planning permission is submitted can ensure these structural decisions are made with the interior in mind. At BD Interiors, this is how we prefer to work on extension projects: not as decorators handed a completed shell, but as designers who help shape the conditions that make a great interior possible in the first place.
The Relationship Between Old and New
How the extension relates to the existing building is one of the most consequential design decisions in the whole project.
One approach is continuity: designing the extension so that it reads as a natural part of the original house, using materials, proportions, and a spatial language that are sympathetic to what already exists. This works well in period properties across Bromley, Chislehurst, and Kent, where the character of the original building is worth honouring.
The other approach is contrast: designing the extension as a clearly contemporary addition that sits in deliberate dialogue with the original structure. A glazed rear addition to a Victorian terrace in Beckenham or a Kent farmhouse, when the proportions and materials are resolved with real care, can be genuinely exceptional. The contrast itself becomes the design statement.
What does not work is a muddled middle ground: neither clearly sympathetic nor clearly contemporary. Clarity of intent is what makes the connection between old and new feel considered rather than accidental.
Getting the Light Right
Light is the most valuable resource in any extension, and it requires deliberate design to make the most of it. South and west facing rear extensions in the properties we work on across South London and Kent have significant potential for natural light throughout the day. North facing extensions require more care: thoughtful roof light placement, generous window proportions, and a material palette that performs well without direct sunlight.
The most common extension types we encounter are single storey rear extensions opening onto kitchen and living areas, and wrap around configurations that combine rear and side return space. Both have distinct light characteristics that require distinct design responses.
In a rear extension with substantial west facing glazing, the challenge in summer is managing heat gain and glare as much as celebrating the light. Roof overhangs, solar control glazing, or well considered planting can all be part of the answer. These decisions are far better made at design stage than resolved retrospectively with blinds that obscure beautifully specified glazing for months at a time.
Designing the Kitchen and Living Extension
The most common use of a single storey rear extension across South London and Kent remains the open plan kitchen, dining, and living space: a rear addition that brings cooking, dining, and relaxing together in one well lit, garden facing room. When designed well, this is the room that changes how a family inhabits their home.
The quality of the design depends on how clearly the zones within the space have been understood and resolved. A kitchen pushed into one corner, a sofa in another, a dining table floating between them: this is not an open plan room. It is three rooms without walls, and it rarely works as well as it should.
Zoning is the key: using changes of ceiling height, flooring material, lighting circuits, and furniture arrangement to create distinct areas within the continuous space, each with their own character and purpose, while remaining connected to each other. This is a design challenge that requires spatial thinking from the earliest stages of the project, not a decision left until the furniture arrives.
Materials That Belong
The material palette of an extension has an outsized impact on how the finished space feels, both within itself and in relation to the rest of the house.
In extension projects across Kent and South London, the most successful approaches establish a clear material logic early: a primary flooring material that runs through the extension and connects to the existing house, a secondary material for the kitchen and joinery zone, and a palette of wall finishes that works in both natural and artificial light.
Natural materials respond particularly well in garden facing extensions. Stone floors warm in afternoon light. Limewashed walls shift in quality through the day. Timber joinery ages well and develops character with use. These are the materials that make a new space feel at home in an old house.
Planning and Permitted Development
Many single storey rear extensions in South London and Kent fall within permitted development rights and do not require planning permission, though the rules vary depending on the property, its location, and whether it falls within a conservation area or article 4 direction zone.
BD Interiors works alongside planning consultants and architects on extension projects where planning consent is required, and we are familiar with the planning landscape across Bromley, Bexley, and the wider Kent boroughs. We can advise on what is likely to be achievable within permitted development and where a planning application is likely to be necessary, before any design work begins.
Working With BD Interiors on Your Extension
BD Interiors works with clients across Bromley, Beckenham, Chislehurst, and throughout Kent, South London, and Surrey on home extension projects at every stage. Whether you are at the early planning stage and want a designer involved in the structural decisions, or you have a completed shell that needs a considered interior design, we would be glad to talk.
Get in touch to arrange an initial conversation with the BD Interiors team.
