Garden rooms
Usually no application
A detached garden building used for purposes incidental to the house, such as an office, studio, gym or hobby room, is permitted development in England if it keeps within the size and position limits below. No application is needed, though a lawful development certificate is worth having for a later sale.
Modular homes
Always full planning permission
A house, an annexe someone will sleep in, or a holiday let is a new dwelling, and permitted development does not cover it. The application is made to your local planning authority and judged on the local plan. We provide planning support and work with your architect or planning consultant.
Guide last reviewed: . Rules are summarised for England; Scotland, Wales and Northern Ireland have their own, and your council can confirm what applies to your plot.
When is a garden room permitted development?
These are the limits for outbuildings under Class E of the General Permitted Development Order in England, as published by the Planning Portal. Every one of them must be met.
Single storey, with a height limit
Maximum eaves height 2.5 m. Overall height no more than 4 m with a dual-pitched roof, or 3 m for any other roof. Within 2 m of a boundary the whole building must be no taller than 2.5 m.
Behind the front of the house
No outbuilding forward of the principal elevation, meaning the wall that faces the road. On designated land (National Parks, the Broads, Areas of Outstanding Natural Beauty, World Heritage Sites) nothing at the side of the house either.
Half the garden stays open
Outbuildings and extensions together may cover no more than 50 per cent of the land around the original house. Pre-existing sheds and extensions count towards the total.
No balconies or raised platforms
No verandas, balconies or platforms more than 30 cm above ground level. A deck at that height or below is fine.
Incidental use only
Offices, studios, gyms, playrooms and stores are incidental. Sleeping accommodation is not: a garden room used as a bedroom or a self-contained annexe needs planning permission.
Not for every property
Permitted development applies to houses, not flats or maisonettes, and not to listed buildings. Councils can remove it locally with an Article 4 direction, and new estates sometimes carry conditions, so check the deeds and the council’s website.
Do garden rooms need Building Regulations approval?
Separately from planning: a detached building under 15 m² of floor area with no sleeping accommodation is exempt from the Building Regulations. Between 15 m² and 30 m² it is exempt if it has no sleeping accommodation and is either at least 1 m from every boundary or built substantially of non-combustible materials. Anything larger, or anything slept in, needs an application. Electrical work must still meet Part P. The Building Regulations guide covers the full house.
Which Trident buildings sit inside the limits?
Floor areas below are from the price guide. Height depends on the roof and base specified for your site, so confirm it on the model page and with your council before ordering.
| Model | Floor area | Usual route |
|---|---|---|
| Garden Base | 4.4–12.2 m² | Permitted development for incidental use, subject to the limits above |
| Garden Premium | 6.5–12.2 m² | Permitted development for incidental use, subject to the limits above |
| Garden Cafe | 14 m² | Permitted development for incidental use, subject to the limits above |
| Garden studio | 15.6–19.2 m² | Permitted development for incidental use, subject to the limits above |
| Part | 54 m² | Full planning permission: a dwelling |
| Riva | 54 m² | Full planning permission: a dwelling |
| Mediterranean Single House | 35.5 m² | Full planning permission: a dwelling |
| Family House | 46.2 m² | Full planning permission: a dwelling |
All garden rooms and the full range of homes.
How does a planning application for a modular home work?
A factory-built house is assessed exactly as a site-built one: on its size, siting, appearance and effect on neighbours, not on how it is made. The application needs location and block plans, elevations and floor plans, and a design statement. The council has eight weeks to decide a householder or minor application once it is validated.
Trident supplies the drawings of the chosen model and the technical description of the building system, and works with your architect or planning consultant on the site-specific parts. Where a plot is tight, the compact houses in the range help: the smallest full home in the catalogue is 35.5 m².
Planning fees, consultants and surveys sit outside every purchase option; see what is excluded on the price guide.
What about an annexe for a relative?
A garden annexe with a bedroom, bathroom and kitchen is treated as residential accommodation and needs planning permission, usually with a condition tying it to the main house. Councils tend to look favourably on an annexe that is ancillary to the house rather than a separate dwelling, so the application should say who will live there and why.
The single-storey homes in the bungalow range are the usual starting point. Under the Turnkey base option the foundation, fit-out and services are included, so the annexe is delivered ready to occupy.
Planning: common questions
How tall can a garden room be without planning permission?
Eaves no higher than 2.5 m, and an overall height of 4 m with a dual-pitched roof or 3 m with any other roof. Within 2 m of a boundary the whole building must be no taller than 2.5 m.
Can I sleep in a garden room built under permitted development?
No. Permitted development covers buildings incidental to the house, such as an office, studio or gym. Sleeping accommodation, a self-contained annexe or a holiday let needs planning permission.
What is a lawful development certificate and do I need one?
A certificate from the council confirming that the building was lawful without permission. It is optional, but it removes doubt when you sell the house, and it is the simplest answer to a neighbour’s query.
How long does a planning application take?
The council has eight weeks to decide a householder or minor application once it is validated, longer if it is called to committee. Pre-application advice before you submit can shorten the process.
More answers on the full FAQ page.
Not sure which route your plot needs?
Send us the address and what you want to build. We will say whether it looks like permitted development or an application, and what the next step is.