A well-designed garden room extends a London home without the disruption of a main-house renovation. Here is what the planning position looks like and what a quality installation involves.
The garden room — a detached structure in the garden used as a studio, office, gym, treatment room, or additional living space — has become one of the most sought-after residential additions in London. The combination of post-pandemic demand for dedicated working-from-home space and the premium on main-house square footage has driven significant growth in the quality and ambition of garden room installations.
Here is what a quality garden room involves and what the planning position looks like.
What a garden room is (and is not)
A garden room is a habitable structure in a residential garden — insulated, heated, connected to power and data, and finished to a standard suitable for regular occupation. It is not a garden shed or a greenhouse.
The distinction matters because garden rooms are subject to different planning rules and require different construction standards to sheds. A shed sits on the ground and is uninsulated. A garden room requires foundations, a structural floor, insulated walls and roof, and services.
Planning permission: the key rules
Most garden rooms in residential gardens fall within permitted development (PD) rights. Under the Town and Country Planning (General Permitted Development) (England) Order 2015, an outbuilding in a garden is permitted development if:
- —It is within the curtilage of the dwelling (within the garden, not on land beyond the boundary)
- —It is single storey with a maximum eaves height of 2.5m and maximum overall height of 4m (pitched roof) or 3m (flat or other roof)
- —The total area of all outbuildings does not exceed 50% of the total area of the curtilage (excluding the area of the original house)
- —It is not used as a separate dwelling (self-contained living accommodation with sleeping and bathroom facilities specifically described as a separate dwelling in planning terms)
- —The property is not listed and not on designated land where outbuilding PD rights are restricted
Conservation areas: In a conservation area, permitted development rights for outbuildings within 2m of the boundary are restricted — the structure must be no more than 2.5m in height. Larger structures or those closer to the principal elevation require planning permission.
Garden within 2m of the boundary: Any part of the structure within 2m of the property boundary has a maximum height of 2.5m under PD rights. For a typical London terrace with a narrow garden and party fences on two sides, this constraint can limit the achievable internal height.
The principal elevation rule: An outbuilding forward of the principal elevation of the house cannot be built under PD rights — it must be behind or to the side.
For any garden room where the planning position is not straightforward, a Lawful Development Certificate from the LPA provides legal certainty.
Design: what makes a quality garden room
Foundations: The foundation system must be appropriate for the ground conditions and the structure. Options: - Concrete pad or strip foundations: suitable for most London garden conditions; requires excavation - Screw pile foundations: fast to install, no excavation, minimal ground disturbance; suitable for light timber frame structures - Ground screws: proprietary metal screws driven into the ground; similar to screw piles, minimal disturbance
The foundation choice affects the cost, the installation time, and the ground disturbance. For a garden with established planting or a mature lawn, minimally invasive foundations are worth the premium.
Structure: Most quality garden rooms use a timber frame structure — either SIP (structurally insulated panel) or a conventional timber stud frame with separate insulation. SIP construction is faster and achieves very good thermal performance; timber stud is more familiar to most contractors and allows greater flexibility in layout and services routing.
Insulation: A garden room used as a home office or studio should be insulated to a standard that allows year-round use without expensive heating. Target U-values: walls 0.18–0.28 W/m²K, roof 0.13–0.18 W/m²K, floor 0.18–0.25 W/m²K. This level of performance requires 100–150mm of insulation in the walls and roof.
Glazing: The character of the garden room is largely determined by its glazing. Full-height glazed panels on the garden-facing elevation, a roof lantern, or frameless corner glazing all create a very different experience from a standard window. Large-format glazing increases cost but transforms the space.
Services: A garden room requires at minimum a power supply from the house (armoured cable buried in the garden at adequate depth — minimum 450mm under a lawn, 600mm under a path or driveway). Power and data for multiple outlets, lighting, and heating. For a high-specification garden room, a separate electricity sub-meter is worth installing.
Heating: Options for a garden room include electric panel heaters (low installation cost, higher running cost), electric underfloor heating (comfortable and invisible), infrared heating panels (fast response, efficient for intermittently used spaces), or an extension of the main house heating system (more complex to install but most cost-effective for heavily used spaces).
High-specification garden rooms
At the top of the market, a garden room is a piece of architecture — designed by an architect to complement the house and garden, built to a high standard of craft, and finished to a specification that matches the main house.
Features at this level include: - Bespoke exterior cladding in timber, zinc, or standing-seam copper - Full-height frameless glazing with automated blinds - Polished concrete or hardwood floor - Built-in joinery (desk, shelving, storage) - MVHR or heat pump heating - Cat6 cabling and dedicated AV installation - Integrated external lighting
A garden room at this specification is a significant addition to the property value — particularly in prime London postcodes where garden size is limited and premium buyers actively seek outdoor studio space.
Cost benchmarks
| Specification | Installed cost |
|---|---|
| Quality timber frame, insulated, basic services, standard cladding | £25,000–45,000 |
| Mid-specification with large-format glazing, hardwood floor | £45,000–80,000 |
| High-specification bespoke garden room | £80,000–150,000+ |
These figures include foundations, structure, services, and finishing. They exclude architect fees where applicable.
ASAAN's approach
ASAAN designs and builds garden rooms as standalone projects and as part of wider garden and renovation programmes. We manage planning, foundations, structure, and services as an integrated project.
If you are considering a garden room, contact us to discuss design options and feasibility for your site.
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