There are no specific provisions or recommendations in planning legislation or guidelines related to the size of basements.
However, the Sustainable Urban Housing: Design Standards for New Apartments Guidelines for Planning Authorities (2018), issued under section 28 of the Planning and Development Act 2000, allow for some internal storage space at basement level. Planning authorities and An Bord Pleanála, as appropriate, are required to have regard to the guidelines in the performance of their functions.
The Guidelines recommend, in section 3.32, that apartment schemes should provide storage for bulky items outside individual units (i.e. at ground or basement level). Secure, ground floor storage space allocated to individual apartments and located close to the entrance to the apartment block or building is particularly useful and planning authorities should encourage the provision of such space in addition to minimum apartment storage requirements. This form of storage may be used for equipment such as, for example, bicycles or bicycle equipment, children’s outdoor toys or buggies. However, such storage does not satisfy bicycle parking requirements.
The Guidelines further recommend, in section 3.33, that where secure, allocated ground or basement level storage is provided, it may be used to satisfy up to half of the minimum storage requirement for individual apartment units, but shall not serve to reduce the minimum floor area required to be provided within each individual apartment unit, as set out in these guidelines. This is intended to enable greater flexibility in apartment design, whereby more living or bedroom space may be provided within the apartment unit in lieu of a portion of required internal storage space where such storage space has been provided elsewhere in the building.
The 2018 Guidelines are available to view on my Department's website at the following link: