Affordable housing is defined in the practice note in the Appendix. In all cases planning applications should clearly set out proposed mechanisms for contributing to local affordable housing need. Where a proposal is fewer than 12 units but is clearly part of a phased development of a larger site which would be subject to an affordable housing requirement, an affordable element will be required at an appropriate stage in the development of the site as a whole. The affordable element should normally be provided on-site. However, provision may be acceptable on an alternative site where the total number of dwellings is below 20, or where all of the following criteria apply there are exceptional reasons to avoid on-site provision, such as the site being poorly located for affordable provision, where conversions do not lend themselves to affordable provision, or there are other advantages to the Council in accepting off-site provision such as achieving more, higher quality or better-located affordable units elsewhere; and an agreed mechanism for delivering the requisite number of affordable units (e.g. through an agreement with a Registered Social Landlord (RSL) at an alternative location elsewhere within the same area of the city is in place; and The proposed alternative site makes an equally satisfactory contribution to meeting unmet local housing needs as the principal development site.