01 — We always do this
Foundations
The difficult part is already done.
- Site set out
- Ground screws installed
- Steel ring beam levelled and set
Self-build garden annexe kits — UK
The engineering is ours.
The build is yours.
A self-build garden annexe with the difficult part already finished. We set out the site, drive the ground screws and level the steel ring beam. You take it from there — on a foundation that is already dead level, already load-tested, and already signed off.
Who does what
- Foundations We always do this
- Shell We can, you can, or your builder can do this
- Fit-out We can, you can, or your builder can do this
Where this sits
The permanence of conventional construction. The speed people associate with factory-built annexes. A price between the two.
- Solid
-
A real building, not a frame with a skin.
Insulated formwork, reinforced and filled with concrete. Doors and windows are hung in a poured wall, not a panel. It is built to read as a small house, not a pod, a cabin or a garden room.
- Fast
-
Built at the pace of a drop-in unit, without dropping the standard.
Ground screws go in without excavation and take load immediately — no dig, no muck away, no slab curing before you can start. The wall system goes up dry and is poured once, so the wet trades are few and short.
- Sensibly priced
-
Between a bare self-build shell and a turnkey factory annex.
You are not paying a factory margin on every visible finish. Neither are you buying a pile of components with the difficult engineering left unresolved. The hard part is settled; the part you have opinions about is still yours.
- Yours to finish
-
Specified by you, not by a production line.
You choose the kitchen, the bathroom, the cladding and the layout of the last 20%. Nobody hands you a fixed specification because it suits their production line. Spend where you want to spend, save where you want to save.
Finishes
The fit-out is yours to specify, not ours to supply. Try a few options on the model.
Cladding
Roof
Windows & doors
Floor
02 — We can, you can, or your builder can do this
Shell
From level steel to weatherproof.
- Build the Creo block walls
- Concrete pour
- Lay roof frame and insulated deck
- Fit EPDM membrane
- Install windows and doors
03 — We can, you can, or your builder can do this
Fit-out
Specify it how you want to live in it.
- External cladding
- Electrics
- Plumbing and drainage
- Heating
- Kitchen
- Bathroom
- Decoration
How it works
Three stages. One handover.
-
01
We always do this
Foundations
The difficult part is already done.
- Site set out
- Ground screws installed
- Steel ring beam levelled and set
-
02
We can, you can, or your builder can do this
Shell
From level steel to weatherproof.
- Build the Creo block walls
- Concrete pour
- Lay roof frame and insulated deck
- Fit EPDM membrane
- Install windows and doors
-
03
We can, you can, or your builder can do this
Fit-out
Specify it how you want to live in it.
- External cladding
- Electrics
- Plumbing and drainage
- Heating
- Kitchen
- Bathroom
- Decoration
Drainage and utility routes need planning before anyone turns a screw. We will walk the site with you first.
On site
Not a visualisation.
A garden annexe first, photographed through its own build. The two sets after it are houses, not garden buildings — the same block and the same pour on a larger job, which is where most of our photography comes from. Every group says which it is.
One already built
A single-storey annexe at the end of a back garden: poured shell, roof deck on, battened out, first fix.
-
Shell up, at the end of the garden -
Battened out, ready to clad -
Rooflight in, roof insulated -
First fix, before lining
Set out and levelled
The perimeter goes down to the drawing before a single course is laid. Photographed on a house build — a garden job is the same sequence at a fraction of the size.
-
Perimeter set out on the cleared plot -
First course, boundary side -
Steel landed onto the wall line -
Guided in by hand
Formwork, then concrete
Dry-stacked and poured once. What sets is a solid reinforced wall. These are house walls — the same block and the same pour, on a bigger building.
-
Interlock — the blocks key together dry -
The core the concrete fills -
Pouring the wall -
Openings formed in the pour, not cut after
Sizes
Three footprints, drawn to scale.
One scale across all three, so the difference between them is the thing you are actually looking at. The internal layout is yours to settle with the drawings.
-
Studio, home office, or a compact one-bed annexe.
28 m²
£54,000 kit, inc VAT
-
A comfortable one or two-bed annexe.
35 m²
£72,000 kit, inc VAT
-
A genuine two-bed annexe with room to breathe.
45 m²
£90,000 kit, inc VAT
Kit prices include VAT and cover the shell as specified under what the kit includes. A fully managed build is priced separately.
Specification
What is in the kit, and what is not.
A shell built to a genuinely high standard. The finishing touches are yours to choose, not ours to impose.
Included in every kit
- Ground screw foundation and precision steel ring beam — screws installed by our approved installer
- Insulated beam and block floor system
- Full ICF wall system, Building Regulations compliant
- Windows and doors, fitted openings, precast lintels
- Roof structure, insulation and EPDM weatherproof covering
- Soffit, fascia and guttering
- Internal partition walls and plasterboard, ready for your own finish
- Full drawings, staged build sequence and wait periods
- Video instruction library
Not included — yours to specify
- External cladding or render
- Electrics, plumbing and heating
- Kitchen and bathroom
- Decoration
- Drainage and utilities connections
Drainage and utilities connections are genuinely site-specific and are quoted separately once your site has been assessed.
- Wall system
- BBA Agrément 21/5850, NHBC and LABC accredited
- Components
- One principal block and one end closure piece — a deliberately small range, so there is less to learn on site and less to get wrong.
Pricing
Two routes. The same foundation under both.
Every price on this page includes VAT. We install the ground screws and the steel ring beam either way — the difference is who takes it from there.
Route one
Self-build kit
Everything you need to build a permanent, fully compliant structure yourself, or with your own trusted builder.
Route two
Fully managed build
Do not want to build it yourself, and do not have a builder of your own? Solvere, our sister company, will build and manage the whole thing — professionally installed, start to finish.
28 days target programme, typically faster
| Size | Self-build kit | Managed build by Solvere |
|---|---|---|
| 28 m² Studio, home office, or a compact one-bed annexe. | £54,000 | Price on application |
| 35 m² A comfortable one or two-bed annexe. | £72,000 | Price on application |
| 45 m² A genuine two-bed annexe with room to breathe. | £90,000 | £129,995 |
All prices include VAT. Managed builds are carried out by Solvere, our sister company. Drainage, utilities and heating are quoted separately once your site has been assessed.
On any size
Staged delivery +£5,000
Materials arrive matched to your build sequence rather than all at once, so you are not storing a whole annexe in the garden from day one.
Optional extras
- Ground and lawn protection £850 – £950 Trackway and sheeting for the duration of the build.
- Underfloor heating upgrade from £4,300 Approximately £4,300 – £4,500 installed.
Speed record scheme
Build it faster than anyone has, and we will pay you for it.
Self-build kits only — Solvere-managed builds are not eligible.
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£1,000
Cashback for any self-build unit completed within 21 days, evidenced.
-
£1,000
Monthly recognition for the fastest verified build each calendar month.
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£5,000
For an outright new national record.
Before you start
An annex someone lives in needs planning permission.
Outbuildings can often go up under permitted development. A self-contained annex — its own bedroom, kitchen and bathroom — cannot. It needs full planning permission, building control sign-off, and it may change your council tax banding.
That is not a reason to walk away. It is a reason to get it right first. We supply the drawings and the technical pack your application needs.
Planning, building control, drainage, cost and warranty — sixteen questions answered
Enquiries
Tell us about the garden.
Email is the quickest way to reach us, and it means you can attach photographs of the spot — which is the first thing we would ask for.
info@rapidannex.comOr call 020 3422 1262
Every job starts the same way: we walk the site with you before anyone turns a screw.
What to put in it
- Roughly where in the garden it would go
- The space you have for it, even approximately
- How a steel beam would reach it — side access, driveway width, overhead cables
- What it is for, and who would be using it