How Much Does a Double Storey Extension Cost in Essex? (2026 Guide)
A double-storey extension cost in Essex runs from £80,000 to £140,000 for a standard 4m wide project in 2026, before kitchen, bathrooms, and decoration are added. Where you land in that range comes down to width, depth, roof type, glazing spec, and what’s going on underground. This guide breaks the cost down element by element, explains why a two-storey extension in Essex actually costs less per square metre than a single-storey one, and sets out realistic budgets for the double storey formats Kirkwood builds most often.
Double Storey Extension Cost Overview
Three formats cover most double storey projects in Essex, and the cost differs meaningfully between them:
- Rear double storey extension (4m wide x 3m deep): from £80,000 to £110,000 — the most common format across Essex by some distance.
- Side double storey extension (3m wide x full depth): from £90,000 to £130,000 — typically adds a bedroom above and a garage replacement or utility room below.
- Rear and side wraparound double storey: from £120,000 to £180,000 — the largest standard double storey format Kirkwood builds.
All three figures cover the shell: the structure, steelwork, roof, window and external door frames, first fix plumbing and electrics, and plastering. None of them includes the kitchen, flooring, decoration, a new staircase, bathroom fitting, underfloor heating, or professional fees; those sit on top. For the full per-m² picture across extension types, see our house extension cost per m² guide, which puts double storey extension cost Essex-wide in context against single storey and loft conversion options.
Here’s the counterintuitive part: double storey costs less per square metre than single storey, not more. A double storey shell typically runs £1,800 to £2,400 per m², against £2,000 to £2,600 per m² for a single storey extension, because both floors share the same foundations and the same roof.
Double Storey Extension Cost Breakdown
Here’s the full element-by-element breakdown for a standard rear double-storey extension in Essex in 2026, real house extension cost examples drawn from actual Essex builds, not generic estimates. Whether you call it a double-storey or a two-storey extension Essex-wide, the same cost structure applies:
| Element | Typical Cost (2026) | Notes |
| Groundworks and foundations | £8,000 – £14,000 | Clay soil or trees may add £8,000–£20,000 for piling |
| External walls (both floors) | £18,000 – £28,000 | Brick outer leaf, block inner, cavity insulation |
| Structural steelwork | £4,000 – £9,000 | Upper floor support, wall removal beams |
| Upper floor structure | £5,000 – £8,000 | Engineered joists, deck, insulation |
| Roof structure and covering | £7,000 – £12,000 | Pitched to match existing is most common |
| Windows and external door frames | £6,000 – £14,000 | First-floor windows; bi-folds at ground floor are more |
| First fix plumbing and electrics | £5,000 – £8,000 | Includes any new bathroom rough-in on the first floor |
| Plastering (both floors) | £4,500 – £7,000 | All walls and ceilings |
| Staircase (if new) | £2,500 – £6,000 | If the project requires a new or relocated staircase |
| External works and making good | £2,000 – £4,000 | Scaffolding removal, reinstatement |
| TOTAL SHELL BUILD | £62,000 – £110,000 | Excludes kitchen, bathrooms, flooring, decoration |
| Professional fees (10–15%) | £6,000 – £16,500 | Design, structural engineering, building regs, Building Control |
| TOTAL PROJECT COST | £68,000 – £126,500 | Before kitchen fit-out, flooring, and decoration |
Kirkwood’s view
The double-storey format Kirkwood builds most often across Essex is a rear extension on a 1930s or post-war semi, typically widening the kitchen at ground floor and adding a bedroom or extending an existing one above. The cost variable clients consistently underestimate isn’t usually the headline build figure; it’s the first-floor bathroom: adding an en-suite or reworking the family bathroom layout upstairs brings extra plumbing, waste runs, and often a structural consideration for where the soil pipe needs to go, and that gets missed when people are focused on the ground floor glazing and kitchen instead.
What Affects the Cost of a Double Storey Extension
Five variables do most of the work in moving a double storey quote up or down.
1. Foundation Conditions
Clay soil paired with mature trees, common across Billericay, Brentwood, Chelmsford, and Wickford, can push the project toward piled foundations, adding £8,000 to £20,000 on top of a standard groundworks figure. Kirkwood’s structural engineers assess this before any quote goes out, not after.
2. Ground Floor Glazing Specification
This is the single widest-ranging line item on any double-storey quote. Standard bi-fold doors run £4,000 to £8,000, premium aluminium sliding doors £8,000 to £16,000, and a structural glass corner detail can add £15,000 or more on its own.
3. Roof Type
A flat roof double-storey extension at ground floor with a pitched roof above is a popular, cost-effective combination. A fully pitched roof matching the existing house costs slightly more but is very often what planning actually requires on a double-storey project, rather than being optional.
4. First Floor Bathroom
If the new upstairs space includes a bathroom or en-suite, second fix plumbing adds £3,000 to £8,000 on top of the standard first fix allowance already in the shell figure.
5. Staircase
A new or relocated staircase, where the project needs one, typically costs £2,500 to £6,000 for a standard specification.
Double Storey vs Single Storey Extension Cost — Which Is Better Value?
Pound for pound, a double storey extension is almost always the better value option. The reason comes down to what you’re actually paying for twice versus once: a double storey extension shares one set of foundations and one roof across two floors, so going from single to double storey typically adds only 60 to 80 per cent to the single storey cost, while delivering 100 per cent more usable floor area.
A concrete example: a 4m x 4m single-storey extension shell might cost around £55,000. The same 4m x 4m footprint built as a double-storey might cost around £88,000, a 60 per cent increase in cost for double the space, 32m² instead of 16m², at roughly the same cost per square metre.
The trade-off is planning. Double-storey extensions almost always need full planning permission, which adds 6 to 10 weeks to the timeline and introduces genuine planning risk that a permitted-development single-storey rear extension doesn’t carry. Which route actually applies to your property is something Kirkwood works out on the Discovery Call, not something to guess at in advance.
Double Storey Extension in Essex — What Planning Is Needed
Double storey extensions almost always need full householder planning permission; they rarely qualify as permitted development, since they typically exceed the height and depth limits that PD allows. In Essex, a double-storey planning application takes 8 to 10 weeks to be determined from submission, and approval is never automatic: councils look closely at overlooking, loss of light to neighbours, and how well the design fits the street.
Design quality genuinely matters here more than on most single-storey projects. Kirkwood designs every double-storey extension with the specific council’s planning policies in mind before anything is submitted, across Chelmsford City Council, Brentwood Borough Council, Basildon Council, Rochford District Council, and Castle Point Borough Council, the councils Kirkwood works with most for double-storey projects.
Kirkwood’s view The most common reason a double-storey planning application runs into difficulty in Essex is overlooking: a new first-floor window that looks directly into a neighbour’s garden or a habitable room next door. Councils weigh this heavily on double-storey applications specifically, because unlike a single-storey extension, there’s genuinely a new vantage point being created where none existed before. At the design stage, Kirkwood addresses this by using obscured glazing, raising sill heights, or repositioning a window entirely on the elevation that faces a neighbour, so the concern is designed out before the application is ever submitted rather than negotiated after a refusal or objection. |
A double storey extension in Essex costs £80,000 to £140,000 for the shell build in 2026, and typically £95,000 to £160,000 once professional fees are added, and pound for pound, it delivers better value per square metre than a single storey extension. The most accurate figure for your own property comes from a Discovery Call, where Kirkwood assesses the planning position, ground conditions, and design options before giving you real numbers. Kirkwood covers double storey projects across Chelmsford, Brentwood, Billericay, Wickford, Basildon, and Rayleigh.
Book a Free Discovery Call
No, you don’t need a registered professional carrying that specific title for a house extension. What you do need is proper planning drawings, structural engineering, and building regulations drawings, and Kirkwood produces all three in-house for extensions across Chelmsford, Brentwood, Billericay, Wickford, Basildon, Rayleigh, Leigh-on-Sea, Southend, and the surrounding areas of Essex.
Frequently Asked Questions
How much does a double storey extension cost in Essex?
From £80,000 to £140,000 for a standard rear or side project in 2026, covering the shell build. Add professional fees, design, structural engineering, and building regulations, typically 10 to 15 per cent, and the total comes to roughly £90,000 to £160,000. Kitchen, flooring, bathroom fitting, and decoration all sit on top of that as separate costs.
Is a double storey extension cheaper per m2 than single storey?
Yes. Going from single to double storey typically adds 60 to 80 per cent to the cost, but delivers twice the floor area. A double storey shell usually costs £1,800 to £2,400 per m², against £2,000 to £2,600 per m² for single storey, because both floors share the same foundations and roof.
Does a double storey extension need planning permission?
Yes, in almost every case. Double storey extensions rarely qualify as permitted development because they typically exceed the height and depth limits PD allows, so a full householder planning application is needed. In Essex, most applications take 8 to 10 weeks to be determined. Kirkwood manages the whole planning process as part of its design service.
What is included in a double storey extension cost?
A shell build figure covers groundworks and foundations, external walls on both floors, structural steelwork, the upper floor structure, roof structure and covering, window and external door frames, first fix plumbing and electrics, and plastering. It doesn’t cover the kitchen, bathrooms, flooring, decoration, a new staircase, underfloor heating, or professional fees.
How long does a double storey extension take in Essex?
From first consultation to completion, typically 10 to 14 months. That covers design (4 to 6 weeks), the planning application (8 to 10 weeks), structural engineering and building regulations (4 to 6 weeks), appointing a builder (2 to 4 weeks), and the build itself (14 to 20 weeks), longer than a single-storey build because there’s a second floor to construct.
What does a double storey extension add to a house?
Space on two floors at once, typically a kitchen-diner or living space at ground level and one or two bedrooms above. In Essex in 2026, a well-designed double-storey extension on a semi-detached home typically adds 10 to 25 per cent to the property’s value, depending on location and specification.
How much does a double storey extension cost on a semi-detached house in Essex?
A semi-detached house extension cost for a double-storey rear project in Essex runs from £80,000 to £120,000 for the shell build in 2026. Semi-detached homes also need a party wall notice before work starts, since the neighbour has to be formally notified and can appoint their own party wall surveyor if they choose. Kirkwood advises on party wall obligations as standard on every double-storey project. For cost comparisons across other extension types, see our house extension costs guide.
What are the planning risks for a double storey extension?
The main risks are overlooking from new first-floor windows, loss of light to a neighbouring property, a design that doesn’t fit the character of the street, and exceeding height limits. Kirkwood designs every double storey extension around the specific council’s planning policies before submission, addressing these risks at the design stage rather than finding out about them at the application stage.
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