Having the Beams team on hand to manage the project and provide extra reassurance on build decisions was incredibly helpful and made the whole experience stress free.
Kerry
London
They have been extremely efficient and reassuring. It was a complex project but they took it all in their stride. They recommended very good contractors who were all punctual, polite and capable.
Andrew
London
All about trust. I felt comfortable with my money, my project, and my home knowing that the outcome would be to my satisfaction or would be made good.
Chris
London
Westminster extension builders who design and build
Westminster is one of the most tightly packed parts of central London, from the mansion blocks of Marylebone and the garden squares of Belgravia to the stucco terraces of Pimlico. Extending a home here usually means working with limited access, shared party walls, and a design that has to sit comfortably within a conservation streetscape.
A joined-up design and build approach means the same team that draws up your extension also understands what Westminster City Council will and won't approve, and how to sequence a build around narrow streets and restricted parking. With Beams, one team handles design, planning and build for your Westminster extension, so decisions made at the drawing board are decisions your builder can actually deliver on site, for one fixed price agreed before work starts.
Types of house extension we build
Beams designs and builds every common type of house extension, matched to your property and the space you want to gain:
Rear extension: extending into the garden to enlarge a kitchen or living space, one of the most common and straightforward types of extension.
Side-return extension: filling in the alley beside a terraced or semi-detached house, often combined with a rear extension to open up the ground floor.
Wraparound extension: combining side-return and rear extensions into a single L-shaped space, giving the largest possible ground floor footprint.
Double-storey extension: adding space on both the ground and first floor, often used to add a bedroom or bathroom above a new kitchen or living area.
What a house extension costs in Westminster
Westminster is one of the most expensive parts of London to build in, so extension costs here often sit toward the higher end of London ranges. Party wall agreements with neighbours, restricted access for skips and deliveries, and the higher specification expected in much of the borough all tend to push costs up compared with the wider London average.
The figures below are general estimate ranges to help with early budgeting, not fixed quotes. Your actual cost will depend on the size and specification of the extension, the condition of your property, and the access available on your street. We'll agree a fixed price once we understand your project.
Project scope | Estimated cost range |
|---|---|
Single-storey side-return extension | £45,000 - £75,000 |
Single-storey rear extension | £50,000 - £90,000 |
Wraparound extension | £80,000 - £140,000 |
Double-storey extension | £100,000 - £180,000 |
Planning permission for extensions in Westminster
Westminster City Council has designated 56 conservation areas, which together cover much of the borough. Many of these conservation areas, and some individual streets within them, also carry an Article 4 Direction. This removes some of the permitted development rights that would otherwise let homeowners build certain extensions without planning permission.
In practice, this means a house extension in Westminster more often needs full planning permission from Westminster City Council than would be the case in many other parts of London, even for extensions that might qualify as permitted development elsewhere. Because the position varies street by street, it's worth checking your specific property's conservation area and Article 4 status before finalising your design. Our designers factor this into the planning strategy for your project from the outset.
Our design and build process
Our process is designed to take the stress out of extending your home:
1. Free estimate and design call: we talk through your project, budget and ideas, and give you an initial estimate at no cost.
2. Design and planning: our in-house designers draw up your extension and manage the planning application on your behalf.
3. Fixed-price build: we match you with a vetted builder, agree a fixed price and milestone payments, and your build is completed with design support throughout.
Why an extension is worth it
An extension lets you gain the space you need without the cost and disruption of moving home, from stamp duty and estate agent fees to the hassle of finding a new property in the same area. For many homeowners, extending is a more straightforward way to get the extra bedroom, larger kitchen or additional living space their family needs.
In a location like Westminster, where suitable larger homes can be hard to find and expensive to buy, extending the home you already have is often the more practical option, while keeping you in the area, schools and community you know.
Extending a home in Westminster
The average house price in Westminster was £877,000, according to provisional ONS and HM Land Registry data for July 2026. That reflects a borough built up largely of period housing, from Georgian and Victorian terraces in Pimlico and Marylebone to the mansion blocks of Maida Vale, much of which was never designed with modern family life in mind. Extending carefully within this stock, while respecting the surrounding streetscape, is often how homeowners in Westminster get the space they need without leaving the area.
Other services in Westminster
We also help Westminster homeowners with:
If you already have a design and simply need a reliable team to build it, we work with vetted Builders in Westminster.
Once the structural work is done, our team can help style the finished space through Interior design in Westminster.
For homes where extending outward isn't possible, a Basement conversion in Westminster can be a good alternative source of space.
Many Westminster homes have unused roof space, and a Loft conversion in Westminster is often a practical way to add a bedroom without altering the footprint.
If your project goes beyond a single extension, our Home renovation in Westminster service covers wider updates across the property.
We also handle Bathroom renovation in Westminster projects, whether as part of a wider extension or on their own.
A Kitchen renovation in Westminster is one of the most popular additions to pair with a rear or side-return extension.
House extensions in nearby areas
We also design and build House extensions in Hammersmith.
And we support homeowners with House extensions in Fulham.
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