Previously planning permission legislation you had to leave a one metre gap between your building and any garden boundary if the internal floor area of your studio exceeded 15 sq metres. That is no longer the case
Provided your building is less than 2.5 m in overall height, then you can now go up to 50% of the area of all your garden. The area of your garden is all your land except the part the house stands on, so the area includes the front garden, side gardens and back garden, less the area of any other buildings, fuel tanks etc.
No buildings are to go in front of the front elevation of the house, same as before.
The 30 sq m max size rule, no longer applies either, the 50% rule replaces it so garden rooms, provided they are single storey, can now be a lot bigger, depending on your garden size.
If you are in a conservation area, then you cannot have anything at the front or side but now, no longer need permission to place a garden room in the back garden within a conservation area. Before you had to ask for permission wherever it was sited, if you were in a conservation area.
Studios within the garden of Listed buildings, you need full planning as before. Within Areas of Outstanding Natural Beauty etc, the rules are the same as before, max size of 10sq metres at least 20 metres away from the house.
You must go for planning permission if it is being used for overnight accommodation whatever area you are in.
This is our understanding at present of the national rules, but some councils have local waivers and variations, always check with your local planners first.
In all cases, building regulations do not apply ONLY if the building does not contain any sleeping accommodation.
Whilst we accept that some people do occasionally use garden rooms from time to time as occasional sleeping accommodation e.g. sleepovers, we would suggest that it is not illegal due to pedantic bureaucrats but because garden rooms are generally far easier to catch fire. This is why they are only exempt from regulations, including fire regulations, provided they are not used overnight.
It is suggested therefore that if they are used for this, no matter how occasionally, then they must be fitted with house regulation compliant mains powered smoke detectors with battery back ups. Your electrician will happily fit one as he connects the studio to your house electrically, furthermore, we suggest you may take the opportunity of having them installed in your house at the same time.
If you intend using your extra room for sleepovers, we will be happy to make the building comply with fire regulations for your safety for an additional charge.
NB. Do always check planning permission with your local authority before you commision any building - Extra Rooms cannot be responsible for any disputes or legal sanctions.