The Short Answer
A garden room costs 40–60% less than an equivalent extension, doesn't require planning permission in most cases, is built in days rather than months, and causes almost no disruption to your home. A house extension gives you internal connected space — but at significantly higher cost, complexity and disruption.
If you need a dedicated home office, studio, gym or relaxation space — a garden room will almost always be the better choice. If you need a new bedroom, kitchen extension or permanently connected living space, an extension may be necessary.
Head-to-Head Comparison
| Garden Room | House Extension | |
|---|---|---|
| Cost (5×3m equivalent) | From £25,460 inc VAT | £60,000 – £90,000+ |
| Planning permission | Usually not required | Often required (8–13 weeks) |
| Build time on site | 3–5 days | 6–16 weeks |
| Disruption to home | Minimal — built entirely outside | Significant — walls opened, trades inside |
| Structural foundations | Ground screws — no concrete, no dig | Concrete strip or raft foundations |
| Building regulations | Electrical cert only (Part P) | Full building control sign-off required |
| Insulation quality | SIPs — U-value 0.18 or better | Varies — often standard cavity wall |
| Year-round usability | Yes — designed for all seasons | Yes |
| Adds property value | 5–15% typically | 10–20% typically (higher cost, lower ROI) |
| Reversible / relocatable | Ground screws can be removed | Permanent |
| VAT | Standard rate (20%) — included in price | Standard rate on labour and materials |
| Typical timeline start to finish | 6–12 weeks | 6–18 months |
Why Extensions Cost So Much More
✓ Garden Room — what's included
From £25,460 inc VAT
5×3m Garden Room, fully installed
£ Extension — typical additional costs
£60,000 – £90,000+ typically
Equivalent footprint, Surrey, 2024 prices
When to Choose Each
Choose a Garden Room if…
Consider an Extension if…
Common Questions
Does a garden room add as much value as an extension?
The absolute value added by an extension is typically higher, but the return on investment from a garden room is often better — you're spending significantly less to achieve a meaningful uplift. A quality garden room from The Green Rooms typically adds 5–15% to property value. Many buyers now specifically look for a garden office or studio as part of the purchase.
Can a garden room replace a home office extension?
For most people, yes — and often better. A garden room gives you complete separation from the house, which many people find improves focus and work-life balance. Our rooms include Cat 6a internet cabling, dedicated electrical circuits, year-round heating and insulation, and can be fitted out exactly to your specification.
Will a garden room affect my council tax?
A garden room used as a private space ancillary to the house doesn't affect council tax. Only structures that could be used as self-contained dwellings would be assessed separately, which doesn't apply to garden rooms.
Is a garden room permanent?
Our ground screw foundations are permanent but removable — unlike concrete, the screws can be extracted with no damage to the garden. The structure itself is permanent, but it's not the same kind of irreversible commitment as knocking down a wall for an extension.
See What a Garden Room Would Cost
Get an instant guide price for your size and specification — or book a free site visit and we'll talk through what's possible in your garden.