How Much Does It Cost to Extend a House in Kew, Richmond, Brentford & Ealing?

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. Here’s what a comprehensive extension budget typically covers:

• Design & surveys: measured survey, concept design, planning drawings, structural calculations.
• Permissions: planning application (if required), building regulations, party wall notices/awards.
• Construction: foundations, structure/steels, walls, roof, insulation, plastering, glazing, external doors.
• Services (MEP): electrics, plumbing, heating/UFH, ventilation and controls.
• Fit-out: flooring, joinery, kitchen/bathroom supply & install (where included), decorations.
• External works: drainage adjustments, steps, patio make-good, basic landscaping allowances.
• Project overheads: site setup, scaffolding, waste removal, health & safety, insurances, management.

Important: clarify whether a quote is shell-only (structure watertight, limited finishes) or a turn-key finish (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/complexity with a good quality finish. Your final total may be lower or higher depending on design ambition, access, conservation constraints and specification.

• Single-story rear extension: £60,000 to £100,000
• Two-story extension: £80,000 to £150,000+
• Loft conversion: £50,000 to £90,000+
• Kitchen extension: £50,000 to £90,000
• Conservatory: £20,000 to £40,000
• Garage conversion: £10,000 to £25,000

Add typical allowances for professional/statutory fees and a prudent 10–15% contingency. VAT treatment varies by scope; most extensions attract standard-rate VAT—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:

• Family kitchen-diner, garden access (rear extension): £70,000–£110,000
• Open-plan living with rooflights & sliders: £95,000–£135,000
• Wrap-around with utility & WC (steelwork + façade changes): £120,000–£170,000
• Two storeys (living below, bedroom/en-suite above): £160,000–£220,000
• Selective basement room (excavation + tanking + MEP): £140,000–£220,000+

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 & logistics: narrow streets, parking controls, limited storage and crane/hoist needs can increase prelims.
• Planning & conservation: parts of Kew and Richmond are conservation-sensitive; expect extra design/detail coordination.
• Ground conditions: clay, tree roots and legacy drains may dictate deeper or piled foundations.
• Structure & spans: large openings for open-plan layouts often need steels and temporary works.
• Glazing & roof design: sliders, roof lanterns and big rooflights elevate experience—and cost.
• Fit-out level: kitchens, bathrooms, bespoke joinery and flooring choices are big budget levers.
• MEP scope: upgrades like UFH, MVHR or heat-pump integration add comfort and value, with added cost.

Local Tips for a Better Outcome

• Kew: early arboricultural/structural input helps where mature trees and root protection are factors.
• Richmond: conservation constraints often favour sympathetic materials and detailing—plan time for approvals.
• Brentford: mixed stock and tight access—book logistics early (skips, deliveries, hoists) to avoid delays.
• Ealing: semi-detached/terraces may trigger party wall procedures—serve notices early to keep momentum.

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.

1. Initial consultation & site review: goals, constraints, budget guardrails.
2. Measured survey & feasibility: options, layouts and outline totals for comparison.
3. Planning/regs strategy: drawings, submissions and building control coordination.
4. Itemised proposal: crystal-clear inclusions/exclusions, realistic allowances, contingency planning.
5. Delivery & QA: programme, quality control, weekly updates and cost transparency.

Prefer to phase? 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

• Freeze the layout early. Design drift is the #1 budget creep.
• Decide the glazing package up front. It shapes structure, programme and cost.
• Confirm kitchen/bathroom specs pre-tender. Big-ticket items drive totals.
• Be realistic on access. Allow for skips, permits, deliveries and cranage if needed.
• Don’t under-allow MEP. Heating, ventilation and electrics make the space liveable.
• Keep a 10–15% contingency. It protects momentum (and sleep).
• Plan decisions weekly. Faster answers = fewer delays and prelims.

Frequently Asked Questions

Can I 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.

How much contingency should I allow?
We recommend 10–15% of the build total to cover unforeseen ground conditions or client-led changes.

Do I need a structural engineer?
Yes—large openings, steelwork and foundation design require calculations and sign-off. We coordinate this as standard.

When is VAT payable?
Most extensions attract standard-rate VAT. We’ll clarify VAT on each line so you can budget accurately.

How long will construction take?
A typical single-storey extension takes around 3-4 months to complete, while a double-storey extension or loft conversion can take 4-6 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.

Form more information, take a look at our Ultimate Guide To Home Extensions In North London and also our A Complete Guide to House Extension Costs in the UK: Everything You Need to Know.