Does a 5x4m (20m²) garden room need building regulations?

A 20m² garden room is exempt from building regulations provided it does not contain sleeping accommodation and is at least 1m from any boundary. If it is less than 1m from a boundary (but the 15–30m² size band applies), it must be constructed of non-combustible materials to remain exempt. Mains electrics still require Part P compliance.

Do I need building regulations for a garden room with a toilet?

Yes. A garden room with WC or bathroom facilities is not a straightforward outbuilding — it requires building regulations approval for Part G (sanitation), Part H (drainage) and potentially Part P. Adding a toilet also changes the PD classification (no longer purely incidental) and may require planning permission.

What is a Part P certificate for a garden room?

A Part P Electrical Installation Certificate is issued by a Part P registered electrician after installing and testing the electrics in a garden room. It confirms the installation complies with BS 7671 (18th Edition) wiring regulations. The certificate is required regardless of garden room size and should be retained for future sales, remortgages and insurance purposes.

Can I regularise a garden room that was built without building regs?

If the room required building regulations and they were not obtained, you can apply for a Regularisation Certificate from LABC. The inspector will visit, assess the structure, and may require opening up of floors or walls to check insulation and foundations. A Regularisation Certificate is required by solicitors when selling a property where an outbuilding required regs but none were obtained.

Garden Room Building Regs London 2025 | Builderr

Do Garden Rooms Need Building Regulations in London?

Garden rooms under 15m² are fully exempt from building regulations in England. Between 15m² and 30m² they are exempt if they do not contain sleeping accommodation and are sited at least 1m from any boundary. Over 30m² building regulations always apply. Structures with mains electrics always require a Part P electrical certificate regardless of size.

Building regulations exemptions for garden rooms

The Building Regulations 2010 (Schedule 2, Class VI) exempt certain detached outbuildings from the regulations. A garden room is exempt from building regulations if it: is less than 15m² floor area (no other conditions apply); OR is between 15–30m² AND does not contain sleeping accommodation AND is at least 1m from the boundary; OR is between 15–30m² AND does not contain sleeping accommodation AND is constructed substantially of non-combustible material. Garden rooms over 30m² always require building regulations approval — you must either give a building notice or submit full plans to your local authority building control (LABC) or an approved inspector.

Electrical installation (Part P) requirements

Regardless of garden room size, any new electrical installation in England must comply with Part P of the Building Regulations. This means: the electrical work must be carried out by a Part P registered electrician (or notified to LABC by a non-registered contractor); a BS 7671 Electrical Installation Certificate must be issued on completion; the new consumer unit or sub-panel in the main house where the garden room circuit originates must be appropriate. Electrics are the most common compliance gap in off-the-shelf garden room packages. Always ask your supplier for confirmation that the electrical installation will be Part P certified — some modular suppliers pass the electrical responsibility to the client. Builderr only installs garden room electrics using NICEIC-registered contractors, and we issue the Part P certificate as standard.

When do building regulations add value?

Even where a garden room is technically exempt from building regulations, voluntarily seeking approval (via a Regularisation Certificate for a completed structure or a Building Notice before starting) has two benefits. First, it gives you a formal record that the structure is structurally sound, thermally efficient and electrically safe — useful when selling or remortgaging. Second, if the room is used as a home office and you want to claim capital allowances or business rates relief, a building regulations certificate helps evidence the standard of construction. For garden rooms over £20,000 construction value, we recommend seeking building regulations approval even where exempt, as the cost (£400–£900 LABC fee) is minor compared to the documentation benefit.

Structural and thermal requirements if building regs apply

Where building regulations do apply (rooms over 30m² or sleeping accommodation), the structure must meet: Part A (structure) — foundations sized for ground conditions; Part B (fire safety) — fire-rated materials within 1m of boundary; Part C (moisture resistance) — damp-proof membrane, vapour control layer; Part F (ventilation) — openable windows and mechanical ventilation if highly airtight; Part L (energy efficiency) — U-values for walls (0.28 W/m²K), floor (0.22 W/m²K), roof (0.16 W/m²K) and glazing (1.4 W/m²K); Part P (electrics) — as above. Achieving Part L standards typically requires: 100mm+ PIR floor insulation, 140mm+ wall insulation, 200mm+ roof insulation, and thermally broken bifold or aluminium windows.