The redevelopment of the city was planned by Sir Patrick Abercrombie in his 1943 Plan for Plymouth whilst simultaneously working on the reconstruction plan for London. Between 1951 and 1957 over 1000 homes were completed every year mostly using innovative prefabricated systems of just three main types; by 1964 over 20,000 new homes had been built transforming the dense overcrowded and unsanitary slums of the pre-war city into a low density, dispersed suburbia. Most of the city centre shops had been destroyed and those that remained were cleared to enable a zoned reconstruction according to his plan. In 1962 the modernist high rise of the Civic Centre was constructed, an architecturally significant example of mid twentieth century civic slab-and-tower set piece allowed to fall into disrepair by its owner Plymouth City Council but recently grade II listed by English Heritage to prevent its demolition.

Answer this question, if possible (if impossible, reply "unanswerable"): In the postwar period to 1964, how many houses were built in Plymouth?
over 20,000