Demolishing a domestic garage is usually exempted development in most cases, as removing a small ancillary structure typically does not require planning permission on its own. However, if the garage is attached to or forms part of a protected structure, or its demolition is linked to other works needing permission, separate rules can apply, so it is worth checking with the local authority first.
Demolishing a standalone or attached domestic garage is generally low-impact development and, in most ordinary cases, does not require separate planning permission, because removing a small ancillary structure does not usually raise the same planning concerns as demolishing a house. This is consistent with the general approach under the Planning and Development Regulations 2001 (as amended), which treats many minor and ancillary works around a dwelling as exempted development, subject to conditions.
The position changes where the garage forms part of, or is attached to, a protected structure or a structure within an Architectural Conservation Area, in which case demolition can require planning permission because any alteration affecting the character of a protected structure is treated more strictly. It can also change if the demolition is one element of a larger development, such as clearing a garage to build a new extension or dwelling, where the overall project may need permission even if the demolition step alone would not.
Because exemptions depend on the specific circumstances of the site, including whether the property is protected, in a conservation area, or subject to a planning condition restricting works, it's sensible to check with the local authority's planning department, or apply for a Section 5 declaration of exemption if there is genuine doubt, before demolishing a garage.