Garden room or garden home: which rules apply?

The short answer

If nobody will sleep or live in it, you are building a garden room under Class 3. If someone will live in it, you are building a garden home under Class 3A. You cannot build a garden room and later move someone into it: a garden room is not for living in.

Garden room (Class 3)

• Home office, gym, studio or store
• Up to 30 m² in total with other sheds and garden rooms (it was 25 m²)
• Up to 4 m high with a tiled or slated pitched roof, or 3 m otherwise
• Not forward of the front wall of the house; to the side, the finishes must match the house
• At least 25 m² of private open space kept
• Not for human habitation
• Building Regulations still apply; no Commencement Notice needed when it is planning-exempt

Garden home (Class 3A)

• A detached house in the rear garden
• At least 32 m², and no more than 45 m² together with existing sheds
• Up to 4 m high with a tiled or slated pitched roof, or 3 m otherwise
• Occupied in conjunction with the main house; cannot be sold or subdivided; no short-term letting
• Main house is the owner's only or main residence when work starts
• At least 0.6 m from boundaries, windows 0.6 m from the boundary they face, and 25 m² of open space kept
• No separate utility connections and no new road access
• Council notified at least 14 days before starting; started and finished by 31 December 2030
• Building Regulations apply as for a new dwelling, with a Commencement Notice

Attached family flat

A third option is accommodation joined to the house. It always needs planning permission, the size is set by the county plan (Fingal, for example, allows up to 75 m²), and it is usually occupied by a family member under a planning condition, with internal access and reversion to the main house. Meath requires it to be attached.

Does my shed count?

Yes, for both. Existing sheds count towards the 30 m² garden room total and towards the 45 m² garden home limit. If you want to keep a large shed, it reduces what you can build. Measure what is already there before you plan.

Why Building Regulations make the biggest difference

Building Regulations apply to both, but a garden home is treated as a new dwelling: fire safety, energy, ventilation, drainage and access all apply as they would to a new house, and a Commencement Notice is needed. That changes the insulation, the services, the bathroom and kitchen, and the cost per square metre.

Services are different too. A garden room can be as simple as a power supply. A garden home needs water, power and drainage, and all of it must run through the main house, because separate utility connections are not allowed.

Which one should you build?

Ask who will use it and how. An office, gym or studio for the household is a garden room. A place for someone to live, occupied in conjunction with the main house, is a garden home. If you want a separate property to sell or to let short-term, neither exemption fits, and you need planning permission.

Both may be exempt if they meet all the conditions. We check your site first, and a Section 5 declaration from the council gives certainty.

What it costs

We price both by floor area, with groundworks, trenching and service connections shown separately, because they depend on your garden and how far services need to run. For a garden home, the service runs from the main house are always part of the cost.