Does a garden room need building regulations approval?

Not normally if your garden room is under 15 square metres with no sleeping accommodation. Between 15 and 30 square metres it is also normally exempt, provided there is no sleeping accommodation, and it is either at least a metre from every boundary or built substantially of non-combustible materials. If you’re creating an insulated garden room, garden office room or another heated living space, you’ll still want good insulation and construction standards even where formal approval isn’t required.