Eryri’s Supplementary Planning Guidance 11 says annexe accommodation should remain ancillary to the main dwelling in design, size, and function and be within its curtilage. It says an annexe must not become a self-contained dwelling separate from the main house. For a new-build annexe, the guidance describes a physical attachment and horizontal link to the main home.
The guidance is local planning material for Eryri/Snowdonia National Park in Wales. It is not a universal rule for Wales or the UK, and it does not determine whether a particular proposal needs permission or will receive it. The design and use of the accommodation, its relationship to the main dwelling, and the exact wording of planning conditions matter.
What to confirm with the authority
Provide the planning history, plans, access and facilities, intended occupants, and proposed use when asking the National Park Authority how the guidance applies. If the unit is already built, confirm what the original permission authorized and whether a condition restricts independent occupation, rental, or sale. A physically self-contained layout does not alone resolve its planning classification.
Planning status is separate from building regulations, title, lawful occupancy, rental permission, and any private agreement. Obtain the authority’s current written advice for the property before relying on the annexe label. This summary describes the local guidance, not a property-specific planning determination.