Not in conservation areas: the maximum area covered by garden structures located more than 20m from any dwelling wall is limited to 10m2. If you choose, you can still have a garden structure larger than 10m2 in your garden. You would just need to seek planning clearance to do so. In most cases, this means applying for a development consent order (DCO). Maximum area of gardens with permanent buildings: including sheds, garages, greenhouses, etc. But not including parking spaces or other non-garden features. Applying this limit to garden rooms means that you cannot have a room that is larger than 10m x 10m. However, there are ways around this limitation. For example, if you were to build a semi-detached house then the front portion could be much larger than 10m2 while the back section is smaller. Or alternatively, you could look at planning permission exemptions which allow for larger gardens with DCOs. There are three main types of exemption: temporary, permanent and permanent residential. Temporary exemptions are only valid for a specified period of time such as one year or until the building receives planning permission. Permanent exemptions are valid forever once granted. Finally, a DCO allowing for a larger garden room than the official limit requires formal approval from an inspector of plans. Such approvals are not common but they can be obtained by paying a fee and providing evidence of funding for local improvements such as new paths or street lighting.