EC is actually considered private property. But in order for the government to cater to a specific sandwiched group, they sell the land to private developers who develop and carry out the marketing of the project themselves.
The only difference is during initial launch, only Singapore citizens with a family nucleus and a combined income of not more than $12,000 are able to purchase this project. Hence, the entry levels during the initial phase is comparable to public housing.
You can consider this form of housing as a form of benefit the government gives the citizens. More information available on hdb website at www.hdb.gov.sg.
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