Everything that makes a garden room easy, the outbuilding rights and the building regulations exemptions, rests on the building being incidental to the house and not being used as sleeping accommodation. Put a bed in it and the exemptions fall away, and what you have is a separate dwelling or an annexe, judged as such.
What sleeping accommodation changes
The building regulations exemption commonly relied on for a small detached outbuilding depends on it containing no sleeping accommodation. Once it does, the building has to meet the full standard for a habitable building: insulation, ventilation, escape in case of fire, protected routes where they apply, and drainage. It is not that a garden bedroom is forbidden, it is that it has to be built properly as one and approved.
Annexe or separate dwelling
Planning then asks a second question: is this an annexe used with the house, or a separate dwelling in the garden. The answer turns on whether it has independent living accommodation, its own access, and whether it could be occupied by someone unconnected with the household. An annexe can often be permitted; a new dwelling in a back garden is a much harder case and has consequences for council tax and for any future sale.
Fire, escape and the distance to the house
A detached building with someone sleeping in it needs an escape route and needs to be considered against the boundary and the house for fire spread. That is why proximity to boundaries matters more once the building is habitable, and it is why the smoke alarm, the door and the window sizes stop being optional details. This is the part most ordinary garden room suppliers do not cover.
A utility room stops short of the line
A garden utility room with a sink, a washing machine and storage stays incidental to the house, so the outbuilding route usually still works. What it needs is a water supply, a drainage route, often pumped back to the house system, and ventilation sized for the moisture a tumble dryer or a washing machine produces. Get the drainage agreed first, because it is the part that decides where the building can stand.
Questions people ask about garden bedroom with ensuite
Can I sleep in a garden room?
Only if it is built and approved as habitable accommodation. The common building regulations exemption for a small outbuilding depends on there being no sleeping accommodation in it.
Is a garden annexe allowed?
Often, where it is genuinely used with the main house. A self contained dwelling in the garden is a separate and much harder planning case.
Does a garden bedroom affect council tax?
A separate dwelling can be banded separately. An annexe used with the house is treated differently, so establish which you are creating.
What does a garden utility room need?
Water in, waste out, usually pumped, and ventilation sized for the moisture. The drainage route normally decides where it can go.