Garden Room or Conservatory: Which Is Right for the Job?

Summary

Garden rooms and conservatories are both popular, relatively low-cost ways to add usable space to a house, and customers frequently ask which one they should have without understanding that they sit under completely different planning and Building Regulations regimes. A garden room is legally and physically a detached outbuilding — it sits apart from the house, has its own foundations, walls, and roof, and (if it has power at all) its own electrical supply run out from the house. A conservatory is attached to the house, sharing a wall (and often a roofline) with the main structure, and its regulatory treatment is built entirely around its relationship to the house — specifically, whether it is thermally and physically separated from it.

This difference drives almost everything else: which permitted development class applies, whether Building Regulations are triggered at all, how the space is heated, what the electrical installation looks like, how it affects the property's EPC and valuation, and even how the space is used day to day. A garden room, once past the incidental-use PD limits, becomes a genuinely separate building that can be lived in, worked in, or used for storage without directly touching the house's own systems. A conservatory, precisely because it's attached, gets special Building Regulations treatment (the "conservatory exemption") specifically because it is not expected to function like a normal habitable room — the moment it starts to (heating tied into the house system, doors removed, solid roof fitted), it loses that exemption and effectively becomes a normal extension.

For trades quoting either job, understanding which regime applies — and where the common trip-wires are that can knock a project out of its exempt status — is essential to pricing accurately and avoiding a customer ending up with an unlawful or non-compliant structure.

Key Facts

• Garden room planning class — GPDO 2015 Schedule 2, Class E (outbuildings incidental to the enjoyment of a dwelling).
• Garden room size thresholds — up to 15m² floor area: fully permitted development, no Building Control notification. 15–30m²: still PD, but only if walls and roof are non-combustible and the building is not used as a bedroom.
• Garden room height limits — 2.5m eaves maximum; 3m ridge for pitched roofs (2.5m overall for flat roofs); reduced to 2.5m overall if within 2m of a boundary.
• Garden room curtilage rule — the outbuilding, combined with all existing outbuildings, must not cover more than 50% of the original dwelling's curtilage.
• Conservatory planning class — GPDO 2015 Schedule 2, Class A (extensions), using the same rear-projection limits as a single-storey extension: 3m for an attached (semi-detached/terraced) house, 4m for a detached house, subject to the 50% land-coverage rule and height limits.
• Conservatory Building Regs exemption — Schedule 2 Class VII of the Building Regulations exempts a conservatory from full Building Regs if it meets specific conditions, including thermal separation from the house by external-quality doors, independent heating (not tied into the main system), and a defined minimum proportion of glazing to roof and walls.
• Garden room electrical supply — any circuit is Part P notifiable; underground SWA cable at minimum 600mm depth (500mm under paving) is standard for the run from the house.
• Conservatory electrical supply — typically an extension of the house's existing wiring rather than a standalone supply, since the conservatory is physically attached and often not treated as a separate electrical zone in the same way a detached garden room is.
• Garden room heating — if used as habitable/incidental space, heating (electric panel heater, electric underfloor, etc.) is normal and does not affect any exemption, because garden rooms are assessed under the outbuilding PD rules, not the conservatory thermal-separation test.
• Conservatory heating — fitting a fixed heating system tied into the main house system removes the Building Regs exemption; independent, separately controlled heating (a standalone electric heater) can be compatible with staying exempt, subject to meeting the other Class VII conditions.
• Foundations — garden rooms typically sit on a concrete pad, screw piles, or shallow strip footing depending on size and construction method; conservatories typically sit on a dwarf wall over a strip or trench-fill foundation, usually deeper than a typical garden room base because they are treated as an extension for structural purposes.
• EPC/valuation treatment — a garden room is generally excluded from the main house's EPC and floor area for valuation purposes, similar to a conservatory; both are typically treated by surveyors as bonus space rather than core habitable floor area, though treatment can vary by surveyor and by how permanently the space is fitted out.
• Article 4 Directions and conservation areas — both garden rooms and conservatories can lose permitted development rights in a Conservation Area, National Park, AONB, or where a local Article 4 Direction removes specific PD rights; always check before assuming either is automatically PD.

Quick Reference Table

Detailed Guidance

Why the attached/detached distinction drives everything else

A garden room is assessed as an outbuilding under Class E of the GPDO — the planning question is about its size, height, and position relative to the boundary and the existing curtilage coverage, and the Building Regulations question is almost entirely about size and combustibility of materials, not about its relationship to the house's heating or thermal envelope, because it has none — it's a separate building. A conservatory is assessed as an extension under Class A for planning, but for Building Regulations it gets a specific, conditional exemption (Class VII) precisely because it is attached and would otherwise need to meet the same fabric standards as a normal extension. That exemption only survives if the conservatory is kept thermally and functionally separate from the house — which is the opposite design intent from a garden room, which is expected to function as its own independent space from day one.

Garden room: the permitted development mechanics

For a garden room used as incidental amenity space (office, gym, hobby room, storage), the relevant limits under Class E are largely about size and construction:

• Under 15m² — fully PD, no Building Control notification required, no restriction on combustible cladding (timber, log cabin construction, etc. are all fine).
• 15m²–30m² — still PD, but only if the walls and roof are non-combustible, and the building is not used as a bedroom. A timber-clad or log cabin structure in this size range needs a planning application, because timber cladding is combustible.
• Over 30m², or any size used as habitable sleeping accommodation, or any size within a designated area beyond the 15m² threshold — a planning application is required.

Height and boundary rules apply regardless of floor area: 2.5m eaves, 3m ridge for pitched roofs, and a reduction to 2.5m overall height if the building sits within 2m of a boundary. See garden rooms for the full detail on construction methods, electrical supply requirements, and Building Regs triggers once a garden room crosses into habitable use.

Conservatory: the Class VII exemption mechanics

A conservatory avoids full Building Regulations only if it meets the Class VII exemption conditions:

• Thermal separation — an external-quality door (or wall) between the house and the conservatory, of a standard equivalent to an external wall/door if the conservatory weren't there.
• Independent heating — the conservatory must not be heated from the main house heating system; a standalone electric heater with its own controls is the typical compliant approach.
• Glazing proportion — a defined minimum proportion of the roof and walls must be glazed (broadly, a conservatory needs to look and function like a conservatory, not a solid-roofed room), and safety glazing rules under Approved Document K apply to critical locations regardless of exemption status.

Losing any one of these conditions — most commonly, removing the door between the kitchen and conservatory for an open-plan look, running a radiator off the main heating system, or replacing a glazed roof with a solid, insulated one — converts the conservatory into a normal extension for Building Regulations purposes, requiring full compliance with Part A (structure), Part L (energy), and Part F (ventilation), typically after the fact if the change happens post-completion. See conservatory planning for full detail on the planning limits and the exemption conditions, and orangery vs conservatory for how this compares to a more solid-roofed, fully-regulated "orangery" style addition.

Electrical and services differences

A garden room's electrical supply is a standalone installation run from the house — typically underground SWA cable, with its own consumer unit, isolator, and RCD/RCBO protection at the building, and it is always Part P notifiable work regardless of the building's PD status for planning purposes. A conservatory, being attached, is far more commonly wired as an extension of the existing house circuits rather than treated as its own electrical installation zone, though the work is still Part P notifiable where new circuits are involved. This is a genuine cost and complexity difference worth flagging to customers comparing the two options on price.

Foundations and structural treatment

Garden room foundations vary by construction method and size — a small timber-frame garden room might sit on a simple concrete pad or screw piles, while a larger or heavier structure (SIPs, masonry-clad) needs a proper shallow strip footing sized to the load. A conservatory, because it is treated as an extension for structural purposes even when Building-Regs-exempt on thermal grounds, typically needs a dwarf wall on a strip or trench-fill foundation similar in principle to (though sometimes shallower than) a full extension foundation — see foundations for foundation depth and type guidance that applies to conservatories and other attached structures.

Choosing between them for a customer

The practical decision usually comes down to what the customer actually wants the space to do:

• Wants separation from the house (a dedicated home office away from household noise, a garden gym, a studio) — a garden room is the better fit, and for most incidental uses under 30m² it can be delivered without a planning application or Building Regulations involvement at all.
• Wants to extend the house itself (more dining or living space directly connected to the kitchen or lounge) — a conservatory (or, if year-round comfort matters more than cost, an orangery-style solid-roofed addition — see orangery vs conservatory) is the better fit, accepting that thermal separation conditions apply if the customer wants to keep the simpler exemption route.
• Budget-sensitive, straightforward outbuilding — garden room, generally the lower-cost and lower-regulatory-friction option for genuinely standalone use.
• Wants the space to feel like part of the house day to day — conservatory, accepting the trade-off that keeping the exemption limits how "integrated" it can be (independent heating, a door rather than open-plan access).

Frequently Asked Questions

Can I use a garden room as a bedroom instead of a home office?

Not under the standard permitted development route. Using a garden room as a bedroom or self-contained annexe removes the "incidental to the enjoyment of the dwelling" basis for Class E permitted development and is likely to trigger both a planning application and full Building Regulations approval (structure, fire, thermal performance, ventilation) as if it were a habitable annexe rather than an incidental outbuilding.

If I remove the door between my kitchen and conservatory, does that affect planning permission too?

It doesn't usually change the planning position (the conservatory's rear-projection dimensions and land coverage stay the same), but it does affect the Building Regulations exemption — removing the thermal separation between house and conservatory means the conservatory can no longer rely on the Class VII exemption and must instead meet full Building Regulations as an extension, including Part L thermal performance for the roof, walls, and glazing.

Which is cheaper, a garden room or a conservatory?

It depends heavily on size, specification, and finish, but a simple timber-frame garden room under the 15m² PD threshold is often the lower-cost, lower-friction option because it avoids both a planning application and Building Regulations involvement entirely for incidental use. A conservatory of a comparable footprint can cost more once foundations, glazing, and compliant thermal separation detailing are accounted for, though a very basic polycarbonate-roofed conservatory can sometimes undercut a well-specified garden room — get comparable specifications quoted before assuming either is automatically cheaper.

Does either a garden room or a conservatory add more value to a property?

Both are generally treated by surveyors as bonus space rather than core habitable floor area, and neither typically adds value on a like-for-like basis with genuine internal floor area added to the main house. A well-built, properly serviced garden room used as a functional home office can be a strong selling point in a market with high remote-working demand; a conservatory that functions as genuine extra living space year-round (rather than being too hot or cold to use) can similarly appeal, but exact valuation impact varies by local market and surveyor judgement rather than a fixed uplift figure.

Can I convert a garden room into a fully habitable annexe later?

Yes, but it requires a planning application (since incidental-use PD rights don't cover habitable annexe use) and full Building Regulations approval covering structure, fire safety, thermal performance, and ventilation as if it were a new small dwelling or granny annexe — plus, potentially, a council tax reassessment. This is a materially bigger and more expensive step than building the original garden room, so it's worth discussing with customers up front if there's any chance they'll want that flexibility later.

Regulations & Standards

• Town and Country Planning (General Permitted Development) Order 2015 (as amended) — Schedule 2, Part 1, Class E (outbuildings) and Class A (extensions).

• Building Regulations 2010, Schedule 2, Class VII — the conservatory exemption from full Building Regulations.

• Approved Document A (Structure) — foundation and structural requirements once an outbuilding or conservatory falls outside its respective exemption.

• Approved Document K (Protection from falling, collision and impact) — critical location glazing safety requirements, applicable to both garden rooms and conservatories.

• Approved Document P (Electrical safety) — Part P notification requirements for any new electrical circuit to a garden room or conservatory.

• BS 7671:2018+A2:2022 — Requirements for Electrical Installations (18th Edition Wiring Regulations), relevant to garden room and conservatory electrical supplies.

• Planning Portal — Outbuildings — official PD guidance for garden rooms and outbuildings

• Planning Portal — Conservatories — official PD guidance for conservatories

• GOV.UK — Approved Document L — Part L requirements relevant when a conservatory loses its exemption

• LABC — Local Authority Building Control — Building Control guidance on outbuildings, conservatories, and the Class VII exemption

• garden rooms — full detail on garden room construction, electrical supply, and Building Regs triggers

• conservatory planning — conservatory planning permission rules and the Part L thermal separation exemption in detail

• orangery vs conservatory — comparison with a more solid-roofed, fully-regulated addition

• permitted development rights — general permitted development rights for extensions

• foundations — foundation types and depths relevant to attached structures like conservatories