Cost to Extend House in Kew, Richmond, Brentford & Ealing

Thinking about adding space with a kitchen-diner, home office or a brighter family room? You're in the right place. This friendly, professional guide from Inventive Designs London explains the realistic cost to extend house across Kew, Richmond, Brentford and Ealing—in clear average total figures, not price per square metre—plus what drives costs locally, how to budget, and how to get a reliable quote.

West London projects often face specific site and planning constraints, but with the right approach you can create spacious, light-filled rooms that feel purpose-built for modern living—without budget surprises.

What's Included in the 'Cost to Extend House'

When you see a total price to extend a house, it usually combines several parts of the journey from sketch to keys. A comprehensive extension budget typically covers design and surveys, including measured survey, concept design, planning drawings and structural calculations. Permissions are also included, such as planning application if required, building regulations, and party wall notices or awards.

The construction phase encompasses foundations, structure and steels, walls, roof, insulation, plastering, glazing and external doors. Services—often called MEP—cover electrics, plumbing, heating or underfloor heating, ventilation and controls. The fit-out includes flooring, joinery, kitchen and bathroom supply and installation where included, plus decorations.

External works such as drainage adjustments, steps, patio make-good and basic landscaping allowances are typically part of the package. Project overheads cover site setup, scaffolding, waste removal, health and safety, insurances and management.

It's important to clarify whether a quote is shell-only—meaning structure watertight with limited finishes—or a turn-key finish that's ready to use. It makes a big difference to the headline total.

Average Total Costs (West London Benchmarks)

Below are typical total ranges we see for well-specified extensions in Kew, Richmond, Brentford and Ealing. The figures are indicative and assume standard access and complexity with a good quality finish. Your final total may be lower or higher depending on design ambition, access, conservation constraints and specification.

A single-storey rear extension typically ranges from sixty thousand to one hundred thousand pounds. Two-storey extensions generally cost between eighty thousand and one hundred and fifty thousand pounds or more. Loft conversions usually fall between fifty thousand and ninety thousand pounds or higher. Kitchen extensions tend to range from fifty thousand to ninety thousand pounds, while conservatories typically cost between twenty thousand and forty thousand pounds. Garage conversions are usually at the lower end, ranging from ten thousand to twenty-five thousand pounds.

Add typical allowances for professional and statutory fees, and a prudent ten to fifteen percent contingency. VAT treatment varies by scope—most extensions attract standard-rate VAT, so plan for it from day one.

Example Scenarios (Real-World Totals)

To help you map costs to outcomes, here are sample totals we regularly see in West London. A family kitchen-diner with garden access through a rear extension typically costs between seventy thousand and one hundred and ten thousand pounds. Open-plan living with rooflights and sliders usually ranges from ninety-five thousand to one hundred and thirty-five thousand pounds.

Wrap-around extensions with utility and WC, including steelwork and façade changes, generally cost between one hundred and twenty thousand and one hundred and seventy thousand pounds. Two-storey extensions with living space below and bedroom with en-suite above typically range from one hundred and sixty thousand to two hundred and twenty thousand pounds. Selective basement rooms, including excavation, tanking and MEP work, usually cost between one hundred and forty thousand and two hundred and twenty thousand pounds or more.

Quick rule of thumb: the simpler the shape and structure, the more of your budget you can allocate to beautiful finishes and glazing.

What Drives the Cost in Kew, Richmond, Brentford & Ealing

Local context matters. These West London neighbourhoods share some common cost drivers that can nudge a project above or below the averages. Access and logistics play a significant role—narrow streets, parking controls, limited storage and crane or hoist needs can increase preliminary costs.

Planning and conservation requirements are important considerations. Parts of Kew and Richmond are conservation-sensitive, so expect extra design and detail coordination. Ground conditions such as clay, tree roots and legacy drains may dictate deeper or piled foundations. Structure and spans matter too—large openings for open-plan layouts often need steels and temporary works.

Glazing and roof design choices such as sliders, roof lanterns and big rooflights elevate the experience but also increase costs. Fit-out level is another major factor—kitchens, bathrooms, bespoke joinery and flooring choices are big budget levers. Finally, MEP scope makes a difference. Upgrades like underfloor heating, MVHR or heat-pump integration add comfort and value, with added cost.

Local Tips for a Better Outcome

Each area in West London has its own characteristics that affect extension projects. In Kew, early arboricultural and structural input helps where mature trees and root protection are factors. Richmond projects often involve conservation constraints that favour sympathetic materials and detailing—plan time for approvals.

Brentford features mixed housing stock and tight access, so it's important to book logistics early, including skips, deliveries and hoists, to avoid delays. Ealing's semi-detached and terraced properties may trigger party wall procedures—serve notices early to keep momentum. Understanding these local nuances helps ensure smoother planning and construction phases.

How We Build Your Quote (and Keep It on Track)

At Inventive Designs London we anchor costs to reality through a discovery-led pre-construction phase. That way, your cost to extend house is grounded in surveys, structure and specification—not guesswork.

Our process begins with an initial consultation and site review to understand your goals, constraints and budget guardrails. We then conduct a measured survey and feasibility study to explore options, layouts and outline totals for comparison. The planning and regulations strategy follows, covering drawings, submissions and building control coordination.

We provide an itemised proposal with crystal-clear inclusions and exclusions, realistic allowances and contingency planning. During delivery, we maintain quality assurance through programme management, quality control, weekly updates and cost transparency. Prefer to phase the work? We can deliver shell-only first and schedule fit-out later, or run a full turn-key programme—your call.

Budget Control: 7 Practical Moves

Smart budget management starts before construction begins. Here are seven practical moves to keep your extension on track financially. First, freeze the layout early—design drift is the number one cause of budget creep. Second, decide the glazing package up front, as it shapes structure, programme and cost.

Third, confirm kitchen and bathroom specifications before tender, since big-ticket items drive totals. Fourth, be realistic on access and allow for skips, permits, deliveries and cranage if needed. Fifth, don't under-allow for MEP work—heating, ventilation and electrics make the space liveable.

Sixth, keep a ten to fifteen percent contingency to protect momentum and your peace of mind. Finally, plan decisions weekly—faster answers mean fewer delays and reduced preliminary costs.

Frequently Asked Questions

One common question we hear is whether you can extend without planning permission. Sometimes smaller rear extensions may fall under permitted development, but conservation areas and design specifics often require full planning. We'll check your property and advise the best route.

Regarding contingency, we recommend ten to fifteen percent of the build total to cover unforeseen ground conditions or client-led changes. Many clients also ask whether they need a structural engineer. The answer is yes—large openings, steelwork and foundation design require calculations and sign-off. We coordinate this as standard.

VAT is another frequent concern. Most extensions attract standard-rate VAT, and we'll clarify VAT on each line so you can budget accurately. Finally, clients often ask how long construction will take. A typical single-storey extension takes around three to four months to complete, while a double-storey extension or loft conversion can take four to six months. We will provide a detailed timeline during the initial consultation.

Final Thoughts & Next Steps

The cost to extend house in Kew, Richmond, Brentford and Ealing is shaped by ambition, site conditions and finish level. With realistic total ranges, a discovery-led design phase and transparent cost control, your extension can be a confident investment.

Share your plans, photos and wish-list with Inventive Designs London. We'll prepare a tailored, itemised estimate and guide you from first sketch to final styling. For more information, take a look at our Ultimate Guide To Home Extensions In North London and also our Complete Guide to House Extension Costs in the UK.