The Extension Company designs and builds these programmes across London and the Hertfordshire border from our Cockfosters base: architectural design, planning, structure and build under one fixed price, with one project lead from first sketch to handover. This page explains what a transformation involves, when it beats a simple extension, what it costs and how to plan one.
What a whole-house transformation actually is
Most substantial houses do not need more space so much as better space in the right places. A transformation treats the whole building as one design problem:
- The extension provides the new volume: a wide glazed rear, a wrap-around, a double-storey addition or a basement level
- The remodel reorganises what already exists: walls opened, stairs moved, layouts redrawn around light and the garden
- The systems are brought up together: heating, wiring, glazing and insulation done once, properly, while the building is open
The result reads as one coherent house rather than an old house with a new room attached, and pound for pound it is how the biggest value uplift gets made: our builders' recent London work includes a family home taken from 120m² to 360m² in exactly this way.
When a transformation beats a simple extension
- The layout is the real problem. If the kitchen is in the wrong place, an extension alone just moves the squeeze. Reorganising while you extend fixes the house once.
- You plan to stay. Serial small projects cost more in total, and each one disrupts the house again. One programme, one disruption, one warranty position.
- The house is dated throughout. When wiring, heating and finishes all need work anyway, doing them inside one programme is dramatically cheaper than doing them twice.
- The plot deserves it. On London’s finest streets, where detached averages run past £1.3 million, a designed transformation is what the plot value has been waiting for, which is why this service anchors our luxury extensions offer.
What a transformation costs in 2026
Every programme is priced on its design, but honest planning bands help before we meet:
| Scope | What it typically includes | Realistic band |
|---|---|---|
| Extension + ground-floor remodel | Glazed rear or wrap-around, kitchen relocated, ground floor opened | £150,000 to £250,000 |
| Double-storey extension + remodel | New rooms up and down, stairs or landings reworked, systems renewed | £250,000 to £500,000 |
| Full transformation | Major extension, every floor reworked, basement where the plot suits | £500,000 + |
Figures exclude VAT, professional fees and kitchen fit-out, consistent with every band on this site; the drivers behind them are unpacked in the luxury extension cost guide. Your quote itself is fixed and itemised, line by line, and the signed figure is the paid figure.
Planning and building control, in one strategy
Transformations usually combine consents: the extension may need a full householder application (double-storey and wrap-around schemes generally do) while some elements sit under permitted development, and internal reconfiguration alone is mostly a building regulations matter rather than planning. We design the consent strategy alongside the architecture: what goes in which application, what gets a Lawful Development Certificate, and how green belt, conservation or estate rules on your specific plot shape the massing. One structural engineer, one party wall strategy, one building control sign-off at the end.
How we run the programme
- Design visit. We walk the whole house, not just the back wall, and talk honestly about how you want to live in it, budget included.
- Whole-house design. One drawing set covering extension, remodel and systems, refined with you until it is right.
- Consents, together. Planning, certificates, structure and party wall handled as one strategy, managed to decision.
- One fixed-price build. A single programme with phased milestones, one project lead, weekly communication, building control closed out and the house handed back finished.