Extensions

Extend your home.
Transform your life.

A well-designed extension doesn’t just add space — it changes how you live. Hutch delivers every type of residential extension across London on a fixed fee, with free structural drawings, complex steel expertise and a dedicated project manager.

Get an instant quote →How it works

At a glance

£2,200

Starting per m²

+£95k

Avg. value added

10wks

Fastest programme

Free

Structural drawings

All extensions include: fixed fee · structural drawings · building regs · planning advice · dedicated PM · 10-year warranty

Types of extension

Which extension
suits your home?

The extension type determines structural approach, planning requirements and cost per m². Here’s a clear breakdown of each option.

What sets us
apart.

⚙️

Complex steel expertise

Large wall removals in a property requires complex steel arrangements, sometimes a box steel (two RSJs welded together) rated for the combined loads above. We’ve installed dozens across London. Our structural engineer sizes the steel precisely — so you’re never over-specified (expensive) or under-specified (dangerous).

🔒

Fixed price — including every add-on

Extensions are where budget surprises hurt most. Bifold doors, rooflights, manhole relocations, demolition of outbuildings — we price everything before we start. The number in your scope is the number on your invoice.

⚠️

Manhole relocation managed

A manhole in the extension footprint is one of the most common surprises on extension projects. We check for manholes at the survey stage, design the solution into the fixed price, and manage the Thames Water process where relevant.

🚪

Glazing specialists — bifolds to slimline

From standard doors to full-width aluminium bifolds to slimline Crittall-style framing — we’ve installed them all and know which systems work in London’s Victorian stock. We advise honestly on specs that deliver value.

🏠

Permitted development advice from day one

Many rear and side return extensions fall under PD — no planning needed. We tell you upfront, apply for an LDC where needed, and manage full planning applications where required. Planning never delays a project we’ve scoped properly.

📐

Free structural drawings on every extension

Extensions always require structural calculations. We include full structural drawings, foundation details and steel specifications — free, on every project. The typical market rate elsewhere is £2,000–£3,000.

Pricing

What does an extension
actually cost?

All London extension prices at standard spec. Final cost depends on size, glazing spec, structural complexity and access.

Extension type	Best for	Programme	Typical cost
Rear — single storey	All house types, most common	10–14 weeks	£2,200 – £2,650/m²
Rear — double storey	Adding bedroom above ground floor ext.	14–20 weeks	£2,600 – £3,100/m²
Side return	Terraces with narrow side alley	10–13 weeks	£2,400 – £2,900/m²
Wraparound	Maximum ground floor footprint	14–18 weeks	£2,700 – £3,200/m²
Basement / lower ground	Where garden space is limited	20–30 weeks	£4,500 – £5,500/m²
Prices at standard spec. All include structural drawings, building regs, project management, party wall if required, and 10-year warranty.

Common add-ons

Bifold doors (3–4 panel)

Aluminium bifold system with full thermal break and hardware.

+£6,000 – £9,000

Slimline aluminium glazing

Crittall-style or Kawneer system — luxury slim-profile frames.

+£10,000 – £15,000

Flat roof rooflights

Fixed or opening Velux rooflights to flat roof extension.

+£3,500 – £6,000

Pitched or lantern roof

Pitched roof to match house or feature lantern over flat roof.

+£4,000 – £8,000

Manhole relocation

Manhole within footprint — relocation or purpose-built chamber.

+£3,500 – £6,000

Demolition of existing structure

Outbuilding, conservatory or garage within the footprint.

+£4,000 – £7,000

The process

From first conversation
to completion.

A typical single-storey rear extension takes 20–26 weeks from first contact to handover. Here’s how each phase breaks down.

Week 1

Free site visit & fixed price confirmed

PM attends site, assesses structural condition, confirms PD eligibility or planning requirement, checks for manholes in footprint, reviews access for materials and waste. Fixed price confirmed within 48 hours of visit.

Weeks 2–4

Structural drawings & scope of works

Structural engineer calculates foundation depths, steel beam specification, and produces drawings for BCO. Detailed scope of works produced — every trade, every material. You sign off before work starts.

Weeks 4–8

Planning / LDC & pre-construction

Planning application or LDC submitted if required. Party wall notices served. Steels, bifolds and long-lead materials ordered. Trades sequenced and booked. Skip permits arranged.

Weeks 8–14

Groundworks & structural frame

Existing structure demolished. Foundations dug and poured. Blockwork walls, steel beam installed over opening, flat roof structure and GRP waterproofing. BCO inspection at structural stage. Roof made weathertight.

Weeks 14–20

First & second fix, finishes

Glazing installed. First fix electrics and plumbing. Insulation, boarding, plastering. Second fix electrics, joinery, tiling, flooring and decoration. Kitchen relocated or redesigned if in scope.

Weeks 20–24

Snagging, BCO sign-off & warranty

Snagging walkthrough with your PM. Building regs completion certificate obtained. 10-year workmanship warranty issued. Full handover pack provided including all certificates and as-built drawings.

Featured project

Double-storey rear extension,
Forest Hill SE23.

£98k

Fixed fee

14 wks

Programme

26 m²

Added area

+£95k

Value added

The project

Victorian mid-terrace in Forest Hill. A double-storey rear extension adding 16m² on the ground floor (kitchen-diner with 2.6m aluminium bifold doors) and 10m² on the first floor (bedroom with en-suite). Box steel over 3.8m rear wall opening. Manhole relocated within the slab. Party wall with both neighbours agreed. Kitchen redesigned as part of the works. Family remained in the property throughout.

Fixed fee: £98,000. Final invoice: £98,000. Completed on schedule.

Key challenges resolved within the fixed price

Box steel over 3.8m opening: Mid-terrace carrying two floors above required a purpose-fabricated box steel. Structural engineer sized it precisely — correct first time.

Manhole in footprint: Found at survey. Designed purpose-built inspection chamber within the extension slab — no Thames Water adoption, no programme delay.

Party wall — two neighbours: Both required formal party wall awards. We managed notices, correspondence and surveyor appointments. Both awards agreed before work started.

Family in residence: Sequenced works to keep kitchen and bathrooms live. Internal hoarding erected. Zero complaints from family or neighbours.

We’d been quoted by three builders before Hutch. Two gave us estimates that felt deliberately low. Hutch gave us a fixed price, a detailed scope, and managed the party wall with both neighbours without us doing a thing. We moved back in on the date they said we would.

Rachel & Paul D.

Double-storey extension · Forest Hill, SE23

FAQ

Extension questions
answered.

Many rear extensions fall under Permitted Development — no planning application needed. For a terrace or semi, you can extend up to 3m under PD (or 6m under the prior approval neighbour consultation scheme). Detached houses get up to 4m (8m under consultation scheme). Double-storey extensions, wraparounds, and any work in a conservation area typically require full planning permission. We advise upfront and apply for a Lawful Development Certificate where needed.

Opening up the full rear wall of your home — typically 5m–7m — requires a box steel: two RSJs welded together to carry the combined load of the floors above. Our structural engineer calculates the exact specification, designs the padstones and bearings, and produces drawings for building control. We’ve installed dozens of box steels across London. This is included in your fixed price.

Manholes in the extension footprint are common on SE London terraces and are one of the most frequent budget surprises with other builders. We check for manholes at the survey stage and design the solution into your fixed price before we start. The most common solution is a purpose-built inspection chamber with access cover within the extension slab — keeping the manhole accessible without Thames Water involvement.

For extensions that build within 3m of a neighbouring foundation or work on a shared wall, the Party Wall Act 1996 applies and formal notices must be served. Hutch manages the entire party wall process — notices, correspondence and surveyor appointments if a neighbour dissents. The cost of your own surveyor is included in your fixed price. A dissenting neighbour’s separately appointed surveyor costs an additional £600–£1,500 which we add transparently.

Standard uPVC or timber doors and windows — included at base price
Aluminium bifold doors (3–4 panels) — adds £6,000–£9,000
Slimline aluminium (Crittall-style) — adds £10,000–£15,000
Flat roof rooflights — adds £3,500–£6,000
Roof lantern — adds £5,000–£8,000

We advise on what’s achievable within your budget and what delivers the best light and space impact for the money.

Yes, most clients live in their property throughout an extension. The main disruption points are: demolition of the existing rear wall (typically 1–2 days), and the final kitchen connection (a few days if the kitchen is being relocated). We plan the sequence to minimise disruption, keep essential services live, and erect internal hoarding to manage dust. The rear of the house is always made weathertight before internal works begin.

Extend your home.Transform your life.

Which extensionsuits your home?

What sets usapart.

What does an extensionactually cost?

From first conversationto completion.

Double-storey rear extension,Forest Hill SE23.

Extension questionsanswered.

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