Quick answer — at equal premium quality, a NOOK Double costs the same or less than a high-spec UK extension, and installs in 2–3 hours instead of 12–18 months.
NOOK Double: £2,600/m² turnkey, fixed price before manufacturing. A premium-spec UK extension starts at £2,800–£4,500/m² base, but once you add architect and project management (+10–12%), 20% VAT, planning fees and the typical 30–40% cost overrun (Houzz UK Renovation Study), the real total lands at £4,200–£6,500/m².
In real terms, NOOK is 35–60% cheaper than a comparable premium extension — with a closed price, a 3-year structural warranty, and installation in a single day.
- Real cost compared: NOOK Double ~£2,600/m² fixed, vs. premium UK extension £4,200–£6,500/m² real (base + architect + VAT + overrun).
- Installation: 2–3 hours with a crane, versus 12–18 months of construction.
- Reversibility: Demountability & Moveability Certificate — officially a moveable asset. If you move, it moves with you.
- Factory-grade build: 14 cm walls with rock wool, 19.7 cm roof with double insulation layer, 12.3 cm floor with XPS. Officially Energy A certified.
- Zero risk: price fixed before manufacturing, 3-year structural warranty, industrial timeline.
1. The two options, defined
What we mean by a traditional extension
An extension built on-site by an architect and builder team: excavation, concrete foundations, structural work, trades in sequence (plumbing, electrics, joinery), finishes and snagging. The result is permanent and valued as an integrated part of the main house. It typically requires full planning permission (or Permitted Development approval), building regulations sign-off, and is subject to the variability inherent in any on-site build: weather, trade availability, on-the-fly decisions, and the well-documented 30–40% cost overrun rate.
What a NOOK prefab garden room is
A modular envelope built entirely in a factory to permanent-building standards, delivered in 10 m² modules and anchored on reversible helical-pile screws. The unit is configured online, leaves the factory fully finished and is installed in 2–3 hours. In the UK, it typically falls under Permitted Development Rights (no full planning application required) because the foundation is reversible and the structure is detached from the main dwelling, with NOOK supplying the full demountability certification pack.
2. The price, in real numbers (UK, 2026)
Comparing prices "per square metre" carelessly is misleading. What matters is comparing equivalent quality tiers and real total cost — not the headline base estimate.
NOOK is premium-spec prefab. The honest comparison is therefore against a premium / high-spec UK extension, not against the market average.
Premium UK extension: £2,800–£4,500/m² base
2026 benchmarks from MyJobQuote, MyBuilder, Rightmove's extension calculator and Homebuilding & Renovating put UK extension ranges at:
- Basic build: £1,400–£1,800/m²
- Mid-range finishes: £1,800–£2,850/m²
- Premium / London spec (comparable to NOOK): £2,800–£4,500/m²
These figures are just the starting point. On top of the base you'll add:
- Architect + project management: +10–12% of the construction budget.
- 20% VAT on labour and materials (most builder quotes are VAT-exclusive).
- Planning / building regulations fees: variable by council.
- Typical cost overrun during construction: +30–40% (Houzz UK Renovation Study).
The real total for a premium single-storey extension in the UK in 2026 typically lands between £4,200 and £6,500/m², with a 30–40% variance above the initial estimate and a 12–18 month timeline.
NOOK Double: £50,740 / 19.5 m² = £2,600/m² turnkey
A NOOK Double is configured online and priced before factory production begins. The £50,740 (from) includes the full structure, premium insulation, double-glazed safety-tempered joinery, waterproof roof, electrical and plumbing pre-installation, helical-pile foundation, transport, crane and installation labour. There are no hidden on-site extras. What you configure is what you pay.
At equal premium quality, NOOK Double is between 35% and 60% cheaper than a comparable premium UK extension once architect, VAT, planning and overrun are stacked on. And it's cheaper with three material differences:
- It's a closed price, not an open-ended estimate.
- It's an officially moveable asset: if you move, it moves with you.
- It's installed in 2–3 hours, not 12–18 months.
What each price includes
| Item | NOOK Double turnkey | Premium UK extension |
|---|---|---|
| Base price per m² | £2,600 fixed | £2,800–£4,500 (estimate) |
| Architect + project management | Not required | +10–12% |
| Planning / building regs | Permitted Development (usually) | Full planning + building regs fees |
| VAT | Included | +20% (on most line items) |
| Transport + crane + install | Included | N/A (on-site build) |
| Typical cost overrun | 0% (fixed price) | +30–40% (Houzz UK) |
| Real total estimated cost | ~£2,600/m² | £4,200–£6,500/m² |
| Real difference | NOOK is 35–60% cheaper at equal quality | |
| Total timeline | 12–16 weeks + 2–3 h install | 12–18 months |
| Reversibility | Dismantle and take it with you | Permanent |
| Structural warranty | 3 years | Depends on contractor |
3. Time, properly understood: peace of mind
Traditional extension: 12–18 months of near-daily decisions
Most clients tell us they're "not in a rush". And for a traditional extension, the raw timeline — 12 to 18 months — isn't usually the problem. The problem is what has to happen during that timeline:
- Get and compare quotes from multiple builders.
- Sign a contract with a chosen firm.
- Engage (or coordinate) an architect and project manager.
- Apply for planning permission and building regs.
- Choose finishes (flooring, joinery, bathroom fittings, kitchen, paint, services).
- Manage suppliers, staged payments, site visits, variations and change-orders.
- Resolve on-site surprises — weekly.
It's a project with work almost every week for the full duration. Every decision counts. Every surprise costs.
NOOK: one decision, 2–3 hours of installation, zero site work
With a NOOK, the process is deliberately different:
- Configure online (15–30 minutes) — model, dimensions, finishes, extras.
- Confirm and pay a deposit.
- Then forget about it. We manufacture for 12–16 weeks.
- Be present on installation day (2–3 hours with a crane).
- Keys and use.
No daily work, no rolling decisions, no on-site surprises. It should be as simple as buying a sofa or any other garden furniture piece: pick it, pay for it, wait for delivery, watch it go into place.
Why the factory beats the weather
On-site construction depends on weather, trade availability, and site logistics. Each is a potential source of delay and cost overrun. A NOOK is built in a controlled environment on an industrial schedule — when we say 12 weeks, it's 12 weeks.
4. Quality, measured in centimetres
"Premium" is often a hollow word. At NOOK we define it with numbers — the actual thicknesses and materials of the envelope:
Walls: 14 cm
- Exterior: thermally-treated Zenwood timber cladding on battens, with a ventilated cavity.
- Insulation core: rock wool in a 70 mm metal-stud profile.
- Technical board: Glassrock or Aquapanel with a breathable membrane.
- Interior: double plasterboard (12 mm + 12.5 mm) ready for paint or wallpaper.
Roof: 19.7 cm
- Exterior: thermally-treated Zenwood on a ventilated batten layer.
- Waterproofing: bituminous membrane.
- Technical board: Glassrock/Aquapanel.
- Double layer of rock wool insulation (48 mm + 70 mm) separated by an air gap — a thermal sandwich impossible to replicate on a conventional site build.
- Interior: double plasterboard (12 mm + 9 mm).
Floor: 12.3 cm
- Finish: parquet over an acoustic foam underlay.
- Base: birch plywood with PVC film.
- Metal-framed structure + XPS insulation (80–110 mm).
- Fibre cement outer layer for protection and thermal inertia.
In some jurisdictions, building regulations require a specific insulation composition; in those cases we substitute rock wool with XPS (or other equivalent materials) without compromising performance. The result is the same: officially Energy A certified across all models, year-round comfort and low running costs.
5. Modularity: not custom, smart
"Prefab" is sometimes confused with "bespoke". NOOK is the opposite. We've designed a 10 m² base module that combines predictably:
- NOOK Base: 1 module = 9.75 m².
- NOOK Double: 2 modules = 19.5 m².
- NOOK Sauna: 1 adapted module = 9.75 m² outdoor Finnish sauna.
Standardisation delivers three concrete advantages:
- Efficient logistics: up to 3 units per lorry, reducing transport cost and carbon footprint.
- Consistent quality: every module is built through the same validated process. No site variability.
- Fixed timeline: we don't depend on bespoke design per client; we build from proven templates.
If you need a fully custom unit with unique geometry, there are studios for that — at a different cost and a different timeline. NOOK is for people who want premium quality without the risk or the price tag of custom.
6. Reversibility: the unit is yours, not tied to the plot
Every NOOK is delivered with a Demountability & Moveability Certificate (in Spanish: Certificado de Movilidad y Desmontabilidad) issued by our technical team. This document confirms that the structure:
- Sits on a reversible foundation (helical-pile screws, no concrete).
- Can be dismantled, transported and reinstalled at another location.
- Is technically a moveable asset (more like a vehicle or equipment than a bricks-and-mortar extension).
Practical implications:
- Planning: in most UK councils, garden buildings on reversible foundations fall under Permitted Development Rights, subject to height, coverage and boundary limits.
- Council tax and valuation: because it isn't permanent construction, it typically doesn't alter the property's rateable band (always confirm locally).
- Moving house: if you sell or relocate, you can take it with you. A NOOK is recoverable capex; a traditional extension is not.
7. What people actually do with a NOOK
"Will I use it enough to justify the price?" is a fair question. These are the most common applications, in rough order of demand:
- Garden office: the most popular use. Hybrid remote work has made the garden office a natural extension of the home. 9.75 m² with acoustic insulation is enough for a full professional workstation.
- Guest room or standalone suite: with optional bathroom and kitchenette, NOOK Double functions as a self-contained dwelling for family or guests.
- Pool house: changing room, shaded lounge area, storage for loungers and accessories, a mini-bar and direct access to a shower. A NOOK Base or Double next to the pool extends the garden's usable season.
- Short-let / Airbnb: self-contained unit with private en-suite; premium glamping rates of £350–£500/night in strong markets (AirDNA comparable listings; actual results vary).
- Private gym or studio: 9.75 m² of clear floor with acoustic insulation — enough for functional training, yoga, pilates or a creative studio.
- Outdoor Finnish sauna: NOOK Sauna with a smart HUUM stove and changing area.
- Personal retreat: a quiet space for reading, meditation or focused work away from the main house.
8. ROI: a worked example with numbers
Scenario: NOOK Double as short-let accommodation
Consider a NOOK Double configured with full bathroom and kitchen, installed on a property with a view and good access. You rent it as a short-let for 50 nights per year at £450/night.
| Item | Amount |
|---|---|
| Initial investment (NOOK Double, configured, average estimate) | £55,000 |
| Booked nights per year | 50 |
| Average nightly rate | £450 |
| Gross annual revenue | £22,500 |
| Operating costs (~25%: cleaning, platform fees, consumables) | –£5,625 |
| Net annual income | £16,875 |
| Payback period | 3–4 years |
| Recurring net income after payback | ~£16,875/year |
This calculation doesn't guarantee results — it depends on location, seasonality, marketing and management — but it illustrates the order of magnitude for anyone with land looking to diversify income. For premium hospitality or glamping markets with rates of £550–£700/night, the same NOOK Double can pay back in 2.5–3 years.
9. Planning, regulations and resale value (UK)
Planning permission
Garden buildings under 30 m² on helical-pile foundations typically fall under Permitted Development Rights, meaning no full planning application is required. The NOOK Demountability & Moveability Certificate is the key document: by certifying the moveable-asset status, the structure is not classified as a permanent extension.
Rules vary by council, and additional constraints apply in conservation areas, listed properties and areas subject to Article 4 directions. NOOK supplies the complete technical pack (drawings, dimensions, loads, materials, certifications) to speed up any paperwork. We recommend checking with your local council before confirming purchase.
Property uplift
Homes with garden offices, pool houses or quality outdoor amenities command a premium on the market. UK listings highlighting "garden office" have grown 1,046% in a decade (Rightmove). Reports from Resi and Rightmove cite 5–15% uplift in sale value when the garden room is well-integrated and maintained.
10. When traditional construction still makes sense
There are scenarios where a traditional extension remains the right answer:
- Structural integration with the main home — extended kitchen, connected living space, internal staircase.
- Modifying the thermal envelope of the main house (converting an enclosed garage to habitable space).
- Facade or roof modifications to the existing house that can't be resolved with a standalone unit.
- No crane access to the garden, making modular delivery logistically impractical.
For everything else — offices, guest suites, pool houses, short-lets, gyms, saunas and retreats — a NOOK wins on time, cost certainty, reversibility and peace of mind.
11. Why NOOK, specifically
"Premium prefab" is a growing category. You can find anything from £700/m² timber kits to £3,500/m² modular builders. NOOK sits at a specific point in the market:
- Online configuration with a closed price. Choose dimensions, finishes and extras; see the price in real time; reserve production with a small deposit. No open-ended quotes.
- Three considered models, not infinite modules. NOOK Base, NOOK Double and NOOK Sauna. Three formats, one quality standard.
- Premium spec as standard on every model. Steel + rock wool + double glazing + Zenwood are the baseline, not an upcharge.
- Installation in 2–3 hours on delivery day, once the foundation is ready (prepared in a prior half-day visit).
- Demountability & Moveability Certificate issued with every unit — officially moveable, reversible, transportable.
- Factory-built across Spain, Germany and Florida, delivered throughout the UK and internationally with optimised logistics.
- 3-year structural warranty plus long-term manufacturer warranties on key components (EPDM, joinery, HUUM stoves).
We're not the cheapest per m², and we don't try to be. We're the prefab you pick when you don't want surprises — not in price, not in timeline, not in quality.
12. Frequently asked questions
What's the difference between a NOOK prefab garden room and a traditional extension?
A NOOK is factory-built and installed in 2–3 hours on a reversible foundation (officially a moveable asset). A traditional extension is built on-site on concrete and is permanent, takes 12–18 months and sees a typical 30–40% cost overrun. At a similar real price per m² (once architect, VAT and overrun are stacked on), NOOK offers total price certainty, a guaranteed timeline and the ability to take it with you if you move.
How much does a NOOK Double cost in the UK?
From £50,740 for 19.5 m² turnkey — approximately £2,600/m². The price includes structure, insulation, double-glazed joinery, waterproof roof, electrical and plumbing pre-installation, helical-pile foundation, transport, crane and installation labour. It's a fixed price, agreed before manufacturing begins.
How much does a premium UK extension cost?
The base price for a premium or London-spec single-storey extension (comparable to NOOK) is £2,800–£4,500/m². On top, add architect and project management (+10–12%), 20% VAT, planning and building regs fees, and the typical 30–40% cost overrun. Real total cost usually lands between £4,200 and £6,500/m², with a 12–18 month timeline. At equal quality, NOOK Double (~£2,600/m² fixed) is 35–60% cheaper in real terms.
Do I need planning permission for a NOOK?
In most UK cases, no. A demountable garden building under 30 m² on helical-pile screws — backed by the NOOK Demountability & Moveability Certificate — typically falls under Permitted Development Rights. NOOK supplies the full technical pack; we recommend confirming with your local council before purchase, especially in conservation areas or properties with Article 4 directions.
How long does it take to install a NOOK?
On-site installation takes 2–3 hours on delivery day: we arrive with the module, crane it into position on the foundation, and connect services. The foundation (helical-pile screws) is prepared in a prior half-day visit. Factory manufacturing takes 12–16 weeks from confirmed order.
Is it insulated well enough for year-round use?
Yes. Walls are 14 cm with rock wool in a 70 mm profile, the roof is 19.7 cm with a double insulation layer (48 mm + 70 mm) and an air cavity, and the floor is 12.3 cm with 80–110 mm of XPS. Every model carries official Energy A certification, confirming four-season thermal performance without costly climate control.
How long does a premium prefab garden room last?
25 years or more. The steel frame doesn't rot, rock wool retains its thermal properties for decades, and the waterproofing membrane carries a long-term manufacturer warranty. The Zenwood thermally-treated exterior needs re-lacquering every 5 years to keep it pristine.
Does it add value to my house?
Yes, when it's well-integrated and maintained. Market estimates place the property uplift at 5–15% of the unit's value. And because it's officially a moveable asset, a NOOK is recoverable capex: if you move house, it can be dismantled and taken with you — something a traditional extension can't offer.
What foundation does a NOOK need?
Helical-pile screws — steel piles wound into the ground. They're reversible, require no concrete, install in half a day and don't damage the garden. They adapt to moderate slopes and preserve natural drainage. This foundation is why most councils don't require full planning permission and why the NOOK can legally be a moveable asset.
Can I customise a NOOK?
Yes, within the modular system. Every NOOK is based on a standard 10 m² module (NOOK Base = 1 module; NOOK Double = 2 modules). You choose interior finishes, joinery, door and window positions, bathroom fit-out, kitchen fit-out and other extras in the configurator. It isn't fully bespoke design — and that's precisely why we can keep timeline and price fixed.
Can I take the NOOK with me if I move house?
Yes. Thanks to the Demountability & Moveability Certificate, a NOOK can be dismantled, transported and reinstalled at another property. It's a key advantage over a traditional extension: the investment isn't tied to the property.
Can I put a bathroom and kitchen in a NOOK?
Yes. NOOK Double is configured with optional full bathroom and kitchenette, with plumbing, ventilation and electrical pre-installation. It becomes a self-contained unit usable as a guest room, short-let, family annexe or secondary residence.
13. Next step
Three models, one standard: premium.
- NOOK Base — 9.75 m² (1 module): office, gym, studio or retreat. From £33,540.
- NOOK Double — 19.5 m² (2 modules): self-contained unit, pool house or short-let with optional bathroom and kitchen. From £50,740.
- NOOK Sauna — 9.75 m² (1 module): outdoor Finnish sauna with smart HUUM stove.
Choose where to start:
- Configure your NOOK online — closed price in 3 minutes, no details required.
- Book a private consultation — 30 minutes with our team, no commitment.
- Download the brochure — technical specifications, finishes and customisation options.
Comparison prepared by the NOOK team in 2026 using UK extension cost benchmarks (MyJobQuote, MyBuilder, Rightmove's extension calculator, Homebuilding & Renovating), the Houzz UK Renovation Study (residential renovation cost overruns), Rightmove and Resi (property uplift with garden office), AirDNA (premium short-let rates) and internal NOOK specifications. Actual results vary by location, execution and market.