National housing requirements are ‘top-down’ and target-driven. The Government sets the national requirements, informed, and supported by the National Housing and Planning Advice Unit (NHPAU) and regional planning bodies. The NHPAU was set up to produce consistent housing supply targets at the regional level. It provides independent advice on affordability matters to the government, regions, and other stakeholders. It makes an input into new housing policies in (RSS). There is a two-tiered planning system made up of RSS and local development frameworks (LDFs). The regions allocate regional housing targets between local planning authorities. The RSS contains housing targets for each local authority district or sub-regional housing market area. At the local level, planning authorities must develop their own policies for the location of new homes and the proportion that will be affordable. The LDF is a folder of documents prepared by local authorities that outlines these policies and provides additional details such as the size and type of housing required, with individual planning briefs for large or strategic sites. Strategic Housing Market Assessments and Strategic Housing Land Availability Assessments provide the evidence base for policies and affordable housing targets.