Extensions & Projects · Essex & East London
A garden annexe or outbuilding can be a home office, a gym, a guest suite, or space for an older relative to live independently while staying close. Done right, it works within permitted development in many cases and doesn't touch your house's own extension allowance.
Types
Which one suits you depends on how the space will be used, how much garden you're happy to give up, and whether it needs to work as independent accommodation.
The simplest outbuilding use - no sleeping accommodation, minimal services, and the most straightforward route through permitted development.
Similar scope to an office, fitted out for exercise or creative use instead.
A bedroom and shower room for visiting family, kept ancillary to the main house rather than fully independent.
Fuller accommodation for a relative, with its own kitchenette and more day-to-day independence.
A detached garage or store - the least involved option, with no habitable use at all.
| Extension type | Build cost | Time on site | Planning | Best suited to |
|---|---|---|---|---|
| Home office / studio | £1,600–£2,400 /m² | 6–10 weeks on site | Usually permitted development | Most gardens |
| Garden gym or studio | £1,600–£2,400 /m² | 6–10 weeks on site | Usually permitted development | Most gardens |
| Guest annexe | £1,900–£2,800 /m² | 10–14 weeks on site | Usually permitted development | Larger gardens |
| Independent living annexe | £2,000–£3,000 /m² | 12–18 weeks on site | Often needs planning permission | Larger gardens |
| Storage / garage building | £1,000–£1,700 /m² | 5–8 weeks on site | Usually permitted development | Any garden |
Costs
We don't build, and we take no margin on the build, so we've no reason to flatter these numbers. They are what Essex builders are quoting our clients in 2026.
Typical garden annexe
£1,500–£3,000 /m²
Around £30,000–£60,000 for a typical 20 m² annexe, built to a good standard.
These figures are build cost only.
Ask three builders and you'll get three numbers. What matters is they're pricing the same specification. That is exactly what a proper technical package gives you.
Costs reviewed August 2026 · next review February 2027
What kind of home is it?
Detached
Semi-detached
Terraced
Bungalow
Our design fee
Not an hourly rate and not a percentage of the build. One figure covering survey, concept design, the planning application and the Building Regulations package, quoted after our first conversation.
Use the design cost calculatorWe price-check builders' quotes against the drawn specification and inspect work as it progresses. You don't have to take our drawings and go it alone.
Stage 5 · construction supportPlanning
Often not, provided the building stays within outbuilding size and height limits and is used for something ancillary to the main house rather than as an independent home.
The maximum garden coverage. All the outbuildings and extensions your house has ever had, combined, can't cover more than half the garden's original area if you want to stay within permitted development - we check this at feasibility, before you commit to a design.
Building Regulations
The difference between a shed and a genuinely usable room is almost entirely down to what's specified here.
Sized for the ground conditions and, where used habitably, insulated to the same standard as the house.
Roof and wall structure specified for the spans involved, especially with vaulted or glazed designs.
Full Part L insulation, unlike a simple garden shed - this is what makes it usable year-round, not just in summer.
Power, water, heating and drainage runs coordinated between the annexe and the main house.
The NSP Stages
Click into any stage for what happens, what you receive, and what comes next.
We look at the garden, the house and your budget, and tell you honestly what's achievable before you spend anything.
We measure the property and garden properly. Everything after this depends on the existing drawings being right.
Options on the table: position in the garden, layout, and how services connect back to the house.
Only where needed - many annexes and outbuildings stay within permitted development.
The package your builder actually prices and builds from, coordinated with the structural engineer.
Quote checking, contractor queries and progress inspections, as much or as little as you want.
Our work
Every project starts as a drawing. These are ours: the plans, elevations and approvals behind the finished rooms.
Add gallery items to show project photos and drawing sheets here.
The stages
Click into any stage for what happens, what you receive, and what comes next.
Honest, early advice on what's realistic for your property, budget and how you want to live.
Options on the table exploring layout, light and flow, so you can react to real ideas.
We prepare and submit the right application, designed to give your scheme its best chance.
The approved concept is developed into a coordinated, buildable set of drawings.
FAQs
Yes, but there's a distinction that matters: an annexe used by a relative while remaining ancillary to the main house is more straightforward under permitted development than one built and used as a fully independent, separate dwelling, which is more likely to need planning permission.
Often not, provided it stays single storey, within the height limits, behind the front of the house, and doesn't take total garden coverage over 50% when added to any existing extensions.
Typically £1,600 to £2,800 per m² depending on how it's used - a simple office costs less than a fully-serviced guest annexe with a kitchenette and shower room.
This gets into planning use and, potentially, mortgage and council tax questions beyond just permitted development - worth a specific conversation with us before you commit to that as the plan.
Yes - any structure intended for habitable use, rather than simple storage, needs full Building Regulations sign-off, covering insulation, electrics, drainage and structure.
You can build close to or on the boundary, though height drops to 2.5m within 2m of a boundary under permitted development, and party wall or party fence wall rules may apply if you're building on the line itself.
Typically 6 to 10 weeks for design and approvals, then a similar period on site depending on size and specification.
We add up everything that's been built since the house was originally constructed, since permitted development coverage limits apply cumulatively, not just to the new building alone.