How is it affordable?
The houses are affordable as they are sold at below the market value. The discount to market value will vary between locations and developments, but we would aim to sell a 3 bed house that might be worth in the region of £180,000 for less than £120,000, or less than 66% of its market value.

How do the houses remain affordable?
Either by a legal agreement or restrictive covenants the houses will never be able to be resold at more than their original percentage of the market value, so a house purchased new at £120,000 which would be worth £180,000 on the open market would never be sold for more than 66% of market value.

If the house on the open market was later valued at £240,000 it could be sold for 66% of this value at £160,000.