Garden Rooms & Offices in North London
Last updated: June 2026 · Figures verified against live North London quotes and current supplier pricing.
Quick answer: The Extension Company designs and builds fully insulated, year-round garden rooms and offices across North London for a fixed price — typically £1,800–£2,800 per m², or £20,000–£50,000 finished. Most are permitted development, so no full planning. Build time: 3–6 weeks.
A garden room is the fastest way to add a proper, usable room to a North London home without the disruption, planning battles or six-figure budget of a full house extension. Done properly — with real foundations, full insulation and mains power — it works in January as well as July, and it goes up in weeks, not months. We are a Cockfosters-based design-and-build company: one team designs your garden room, prices it as a fixed quote, and our build partner Pinegrove constructs it. No subcontractor merry-go-round, no surprise costs at the end.
What does The Extension Company build?
We build permanent, insulated garden rooms designed for year-round use — not summerhouses, not flat-pack kits. Every build is bespoke to your garden, your use and your budget, and every quote is fixed before we start.
- Fully insulated, year-round structures. Floor, walls and roof are insulated to a standard that keeps the room warm in winter and cool in summer, so it is genuinely usable 365 days a year — not a fair-weather shed.
- Design-and-build, one team. We handle design, the planning position, foundations, structure, electrics and finish in-house with our build partner Pinegrove. One point of contact from first sketch to handover.
- Fixed price. You get an itemised, fixed quote after a free site visit. The number we agree is the number you pay — foundations, electrics and VAT included, not bolted on later.
- Built to last. Proper concrete or screw-pile foundations, treated timber frame, quality cladding and a 3–6 week build by an experienced North London crew.
Around 80% of the garden rooms we build are used daily, year-round — home offices, studios and gyms — rather than seasonal garden retreats, which is exactly why the insulation and foundation spec matters.
What can a garden room be used for?
The structure is similar; the internal spec and services change with the use. Below are the most common briefs we build in North London, with realistic finished, all-in costs (foundations, electrics and VAT included) for a year-round room.
| Use | Typical size | What it includes | Finished cost (North London, 2026) |
|---|---|---|---|
| Garden office | 10–15 m² | Insulation, power, lighting, data, double glazing | £18,000 – £35,000 |
| Studio / hobby room | 12–18 m² | As office, plus enhanced lighting/acoustics | £22,000 – £38,000 |
| Garden gym | 15–25 m² | Reinforced/rubber floor, ventilation, power | £28,000 – £45,000 |
| Snug / TV room | 12–18 m² | Insulation, heating, power, glazing | £22,000 – £38,000 |
| Garden room with kitchenette + bathroom | 20–30 m² | Plumbing, drainage, kitchen, WC/shower | £30,000 – £55,000 |
Three things drive the price within each band: size (the single biggest factor), how much glazing you want, and whether you add water and drainage. A garden office with a single socket and a window sits at the bottom of its range; the same footprint with a bathroom and bifold doors sits at the top.
As a recent example of the upper end, we built a 55 m² garden room with a full kitchen and bathroom — effectively a self-contained garden space rather than a single-use office. That scale of project is where plumbing, drainage and a larger foundation push costs toward the top of the table, but it shows what is possible in a North London garden.
Do you need planning permission for a garden room?
This is the single biggest selling point of a garden room, and it is worth understanding clearly. Most garden rooms in North London are permitted development — meaning no full planning application — provided they stay within the rules. We confirm your exact position before you commit.
Your garden room is normally permitted development if all of the following are true:
- It is single-storey, with eaves no higher than 2.5m.
- The maximum height is 2.5m if it sits within 2m of any boundary; otherwise up to 3m (or 4m for a dual-pitched roof) elsewhere in the garden.
- It is not used as self-contained living or sleeping accommodation — a bedroom or independent annexe needs full planning permission.
- It covers no more than 50% of the total garden area.
| Situation | Planning position |
|---|---|
| Single-storey, ≤2.5m near boundary, office/gym/studio use | Usually permitted development |
| Within 2m of boundary, height kept to 2.5m | Permitted development (height-limited) |
| Used for sleeping / as a separate annexe | Full planning permission required |
| Listed building or conservation area | Restricted — check before building |
| Covers more than 50% of the garden | Full planning permission required |
Three practical points. First, conservation areas (Monken Hadley, parts of Highgate, Winchmore Hill, Hadley Wood) and listed homes have tighter rules, so we always check first. Second, even when you do not need planning, a Lawful Development Certificate (£274) is a wise, low-cost way to prove the build is legal — useful when you sell. Third, building regulations apply separately to planning: they kick in if the room is over 15 m², sits within 1m of a boundary, or has sleeping accommodation. We handle all of this for you.
How does it work? Four steps
We keep the process simple and predictable, which is how a typical garden room goes from enquiry to finished room inside a couple of months.
- Free site visit. We come to your North London garden, measure up, talk through how you'll use the room, and check the planning and building-regs position on the spot.
- Fixed quote and design. You receive an itemised, fixed-price quote and a design for your exact garden — foundations, electrics and VAT all included, nothing hidden.
- Foundations and build. Our build partner Pinegrove lays proper foundations, erects the insulated timber frame, fits cladding, glazing, electrics and internal finishes. Most builds take 3–6 weeks on site.
- Handover. We hand over a finished, decorated, powered room ready to use — plus your Lawful Development Certificate paperwork where relevant.
Because one team owns the whole job, there is no gap between trades and no finger-pointing if something needs adjusting — over 90% of our build timeline is continuous work on your site, not waiting on subcontractors.
Why do foundations and insulation matter?
It is tempting to compare our quote with a cheap online "garden room" kit, but you are not comparing like with like — and the difference shows up in winter and at resale.
- Foundations. A proper concrete or screw-pile foundation (£1,500–£5,000 of the build) stops the structure shifting, sinking or twisting on North London's clay soils. Cheap kits often sit on paving slabs or a timber frame on the ground, which moves with the seasons and can rot.
- Insulation. Full floor, wall and roof insulation is what separates a year-round room from a summerhouse. Without it, a "garden office" is unusable for the three or four coldest months — so you have effectively paid for a room you can use two-thirds of the year.
- Glazing and weatherproofing. Double glazing, proper flashing and a sealed building envelope keep heating costs down and condensation out. Single-glazed, poorly sealed kits sweat and leak.
- Electrics and compliance. A mains supply on its own certified circuit, installed to current regs, means you can heat, light and work in the room safely and legally — not run an extension lead across the lawn.
Spend the money on the parts you cannot see — the foundation and the insulation — and the room lasts decades and adds value. Skimp on them and you have an expensive shed.
Which areas of North London do you cover?
We are based in Cockfosters and build right across North London and the bordering Hertfordshire towns. Our crews regularly work in:
- Cockfosters, Hadley Wood and Barnet (EN4, EN5) — larger gardens, higher-end garden rooms and studios.
- Enfield, Southgate and Oakwood (EN1–EN3, N14) — the widest mix, from compact garden offices upward.
- Winchmore Hill, Palmers Green and Muswell Hill (N21, N13, N10) — period homes where careful design matters.
- Potters Bar and surrounding Hertfordshire (EN6) — semis and detached homes with good garden access.
See every town and postcode we serve on our locations page. Wherever you are in North London, the free site visit and fixed quote work the same way.
Frequently asked questions
How much does a garden room cost in North London? A fully insulated, year-round garden room typically costs £20,000–£50,000 finished, or £1,800–£2,800 per m². A 15 m² garden office for year-round use lands around £25,000–£38,000 all-in, including foundations, electrics and VAT. We give a fixed quote after a free site visit.
Do I need planning permission for a garden room? Usually not. Most garden rooms are permitted development if they are single-storey, under 2.5m high near a boundary, cover no more than 50% of the garden, and are not used for sleeping. Conservation areas and listed homes are restricted. We confirm your exact position at the site visit.
Can a garden room be used all year round? Yes — that is the whole point of how we build. Full floor, wall and roof insulation, double glazing and a proper heating-ready electrical supply mean the room stays comfortable in winter and summer, unlike an uninsulated summerhouse or flat-pack kit.
How long does it take to build a garden room? Most garden rooms take 3–6 weeks on site once foundations begin, depending on size and whether services like plumbing are involved. The free site visit, design and fixed quote come first, so the whole process from enquiry to finished room is typically a couple of months.
Can I have a kitchen or bathroom in my garden room? Yes. Adding a kitchenette or bathroom means running water supply and drainage, which pushes a garden room toward the £30,000–£55,000 range. We have built a 55 m² garden room with a full kitchen and bathroom. Note that sleeping accommodation requires full planning permission.
Thinking about a garden room or office in North London? Use our Extension Builder to size and price your room in minutes, or book a free site visit for a fixed, itemised quote. Call 020 3051 9430 to talk it through with the team in Cockfosters.