Garden rooms have become one of the most popular home improvements in the UK, used as offices, studios, gyms, and extra living space. But one of the most common questions homeowners ask is:
“When does a garden room require Building Regulations approval?”
The answer depends on size, use, location, and how the building is constructed, not simply what you call it. This article explains the rules clearly, including the often-misunderstood 1-metre boundary rule. I’ve been working on garden building construction now for over 10 years, and this question is an essential part of the planning stage for any garden room build.
If you’re thinking of building your own garden room, this guide will help you decide whether you need to involve building control or if you’re good to start building.
This guidance applies to England and Wales. Scotland and Northern Ireland have different regulations.
Table of Contents
- What are Building Regulations?
- When a Garden Room Does Not Require Building Regulations
- Garden Rooms Between 15 m² and 30 m²
- Garden Rooms Over 30 m²
- Sleeping Accommodation: The Automatic Trigger
- Plumbing, Toilets, and Kitchens
- What Still Applies Even If the Garden Room Is Exempt
- Quick Summary
- Need Advice on Your Specific Garden Room?
- Garden Room Building Regs FAQs
What are Building Regulations?
Building Regulations, or building control, are national standards designed to ensure buildings are:
- Structurally safe
- Fire safe
- Energy efficient
- Accessible and hygienic
Unlike planning permission, Building Regulations focus on how a building is constructed and used, not how it looks. If you need to understand if your garden room is permitted, my other article describes all the requirements and restrictions for planning permission for your garden room.
When a Garden Room Does Not Require Building Regulations
A garden room is normally exempt from Building Regulations if all of the following conditions are met.
1. It is single storey and detached
The exemption only applies to detached outbuildings, not extensions or attached structures.
2. It contains no sleeping accommodation
This is critical.
If the building is used, or intended to be used, for sleeping (including guest rooms, annexes, or Airbnb use), Building Regulations will be required regardless of size.
3. The internal floor area is 15 m² or less
If the internal floor area is 15 m² or under, the building is fully exempt from Building Regulations, even if:
- It is right up against a boundary
- It is timber-built
- It is insulated and heated
The 1-metre boundary rule does NOT apply to garden rooms under 15 m².
This point is frequently misunderstood.
Garden Rooms Between 15 m² and 30 m²
Garden rooms with an internal floor area between 15 m² and 30 m² can still be exempt, but extra conditions apply.
To remain exempt, the building must:
- Be single storey
- Contain no sleeping accommodation
- And either:
- Be at least 1 metre from any boundary, OR
- Be constructed substantially of non-combustible materials (e.g. masonry)
The 1-Metre Boundary Rule Explained
The 1-metre boundary rule exists for fire safety reasons and only applies to garden rooms between 15 m² and 30 m².
If a garden room in this size range is:
- Less than 1 metre from a boundary and
- Built from combustible materials (such as timber)
Building Regulations approval will be required.
Garden Rooms Over 30 m²
Any garden room with an internal floor area over 30 m² will require full Building Regulations approval, regardless of:
- Distance to boundary
- Construction type
- Intended use
Sleeping Accommodation: The Automatic Trigger
If a garden room includes sleeping accommodation, it always requires Building Regulations approval, no matter how small it is.
This includes:
- Bedrooms
- Guest rooms
- “Occasional” sleeping use
- Granny annexes
- Holiday lets or short-term rentals
Calling it an “office” does not override its actual or intended use.
Plumbing, Toilets, and Kitchens
Adding plumbing can also trigger Building Regulations, especially if the garden room includes:
- A toilet
- A shower
- A kitchen connected to mains drainage
Some off-grid solutions (e.g. composting toilets) sit in a grey area and should always be checked with local Building Control.
What Still Applies Even If the Garden Room Is Exempt
Even where Building Regulations approval is not required:
- Electrical work must comply with Part P
All fixed electrics must be installed and certified by a qualified electrician. - Planning permission rules still apply
Height limits, boundary positioning, and permitted development rules are separate from Building Regulations. - Fire safety and neighbour considerations still matter
Particularly where buildings are close to boundaries.
Quick Summary
- ≤ 15 m², no sleeping → ❌ No Building Regulations (boundary distance irrelevant)
- 15–30 m², no sleeping → ❌ No Building Regulations if 1 m from boundary or non-combustible
- Over 30 m² → ✅ Building Regulations required
- Any size with sleeping accommodation → ✅ Building Regulations required
Need Advice on Your Specific Garden Room?
Every project is slightly different. If you’re unsure whether your garden room requires Building Regulations approval, factors like size, use, boundary distance, and construction method all matter. This Case Study Garden Room with shower and toilet will help you understand the process in more detail.
A quick professional check at the design stage can save time, cost, and problems later.
Garden Room Building Regs FAQs
Does a 20m² garden room with a toilet and shower need Building Regulations approval?
Yes. Adding a toilet and shower normally brings the project within scope of Building Regulations (particularly for drainage, ventilation, electrics and hygiene), and your proposed size (around 20m²) plus location near a boundary also affects exemption status.
Is a garden room between 15m² and 30m² ever exempt from Building Regulations?
Sometimes. A detached, single-storey outbuilding between 15m² and 30m² can be exempt if it contains no sleeping accommodation and is either at least 1 metre from any boundary or constructed substantially of non-combustible materials. If those conditions aren’t met, approval is usually required.
What if my garden room is within 1 metre of the boundary and built from timber?
Timber is a combustible material. If your detached garden room is between 15m² and 30m² and it is within 1 metre of the boundary, you’ll typically need Building Regulations approval because the usual exemption condition (1 metre from boundary or substantially non-combustible construction) won’t be satisfied.
Who do I notify to get Building Regulations approval?
You notify Building Control. You can apply either to your local council’s Building Control team (Local Authority Building Control) or use an Approved Inspector (private building control). Either route can lead to a Completion Certificate if the work complies.
Should I use a Full Plans application or a Building Notice?
For a garden room with a WC and shower, a Full Plans application is usually recommended because it allows Building Control to check your drawings and specifications before work starts (helpful for drainage, fire safety near boundaries, insulation and ventilation). A Building Notice can be quicker but carries more risk of changes mid-build.
What drawings and information will Building Control typically want?
Common requirements include a site plan showing boundary distances, floor plans and elevations, foundation and structural details, wall/roof/floor build-ups (including insulation), drainage layout for the WC and shower, ventilation approach (extract fans), and notes on the electrical installation/certification route.
Which parts of the build are checked under Building Regulations?
Building Control typically checks structure (foundations and framing), fire safety (especially near boundaries), drainage and plumbing for the WC/shower, ventilation, insulation and energy efficiency, and electrics. Depending on the design, they may also look at access/threshold details and moisture protection.
How does fire safety affect a timber garden room close to a boundary?
Fire spread risk is a key issue near boundaries. Building Control may require fire-resisting construction to the boundary-facing wall, restrictions on openings (such as windows) facing the boundary, and specific lining/cladding solutions to reduce the risk of fire spreading to neighbouring land.
What Building Regulations topics apply to the toilet and shower?
Expect checks on foul drainage layout, pipework gradients, traps and ventilation, and suitable inspection access where required. Ventilation for the shower/WC (extract fans) is also important, along with water safety/hygiene requirements and electrical safety in bathroom zones.
Do the electrics still need to comply even if a garden room is “exempt”?
Yes. Fixed electrical installations must comply with Building Regulations (Part P). In practice this usually means using a suitably qualified electrician who can test and certify the work, with paperwork provided at the end of the job.
What inspections should I expect during the build?
Typical inspection stages include foundations (before pouring concrete), drainage (before backfilling), structural frame, insulation (before closing up walls/ceilings), and a final inspection at completion. Your Building Control body will confirm the exact stages for your project.
What certificate do I get at the end and why does it matter?
Once the work passes the final inspection, Building Control issues a Completion Certificate (or equivalent). This is important for resale, mortgages, insurance, and proving the work was carried out legally and to the required standard.
Is Building Regulations approval the same as planning permission?
No. Planning permission and Building Regulations are separate systems. Planning controls things like location, height, appearance and permitted development rules. Building Regulations cover how the building is constructed (structure, fire safety, drainage, electrics, insulation, ventilation, etc.). You may need one, both, or neither depending on the design.
What information should I confirm before starting work?
Confirm your internal floor area, exact distance to all boundaries, whether the building will ever be used for sleeping, and your drainage connection route. If you’re close to a boundary and building in timber, it’s especially important to agree the fire-safety approach with Building Control before starting.
Official Government & Planning Portal Guidance
- Planning Portal – Building Regulations for Outbuildings (Official)
Covers exemptions for detached buildings under 15 m², conditions for 15–30 m², and boundary requirements:
https://www.planningportal.co.uk/permission/common-projects/outbuildings/is-building-regulations-approval-needed-for-an-outbuilding - Planning Portal – Outbuildings & Permitted Development Overview
Useful context on permitted development and planning rules for garden buildings:
https://www.planningportal.co.uk/permission/common-projects/outbuildings/planning-permission - UK Gov – Building Regulations Approval Overview
Government page explaining what building regulations approval is and when it’s needed (general reference on scope, separate from planning permission):
https://www.gov.uk/building-regulations-approval - Gov.uk Technical Guidance on Permitted Development Rights
Official guidance to understand planning permissions and permitted development criteria, which often accompanies outbuildings guidance:
https://www.gov.uk/government/publications/permitted-development-rights-for-householders-technical-guidance/permitted-development-rights-for-householders-technical-guidance - Building Regulations – Wales Government (if your audience covers Wales)
Official Welsh Government guidance on building regulations exemptions for outbuildings too:
https://www.gov.wales/building-regulations-outbuildings
