Middle-income families looking to buy a four-room flat for the first time will be eligible for a housing grant that was previously eligible only for buying two-room or three-room flats, said Prime Minister Lee Hsien Loong on Sunday.

Announcing the extension of the Special Housing Grant (SHG), Mr Lee reiterated in his National Day Rally that the Government was committed to making HDB flats more affordable, especially for the less well-off.

The SHG started out in 2011 as a special subsidy for households earning $2,250 or less, and buyers were limited to two-room or three-room flats.

With the extension, and the income ceiling raised, these first-time buyers can now opt for a four-room flat, and still qualify for up to $20,000 more in subsidies.

"I will make sure every Singaporean family who is working can afford their home," said Mr Lee.

But he outlined competing concerns that emerged from the Our Singapore Conversation. Though many wanted to make sure their children had affordable housing, they wanted the own properties to appreciate in value as well.

To this end, PM Lee said the Government would keep built-to-order (BTO) flat prices stable, while increasing support for lower- and middle-income families, he added.

Mr Lee also acknowledged that maintaining equity had become harder as Singapore's income gap widens, and said the Government had to intervene more to keep "ours a fair and just society".

In the past two years, the Housing Board had built record number of flats to clear first-timer backlog, de-linked new flat prices from the resale flat prices to stabilise built-to-order flat prices, and raised income ceilings to relieve the "sandwich class" among other measures.

He promised that the Government would continue to monitor housing affordability closely, saying that housing "has been and will continue to be an important way to share the fruits of our progress with all Singaporeans, and level up poorer households".

But Mr Lee asked that Singaporeans treat their HDB flats as a "home where we sink roots, raise families and build emotional bonds with fellow Singaporeans", and not see it as just a roof over their heads or a valuable nest egg.