The suburb of Chermside in northern Brisbane has been identified by National Australia Bank (NAB) as a risky investment suburb.

NAB, which blacklisted Chermside late last October, said buyers in the suburb would need a full 20% deposit to secure a home loan. While no northern suburbs have slipped into the highest risk category (which requires borrowers to have a 30% deposit), Chermside, along with Brisbane City, Spring Hill, Bowen Hills, and West End, were identified as medium risk suburbs.

According to CoreLogic RP Data, the median price for homes in Chermside this September was $560,000. The median price for units during the same period was $369,000. This means buyers would need a deposit of $112,000 for a home and $73,800 for a unit to secure a home loan with NAB.

In contrast, buyers in neighbouring Geebung would need just $25,000 for a typical 5% home loan minimum deposit on a median-priced $500,000 house, or $14,087 for a median-priced unit one suburb further out in Zillmere.

To gauge affordability, note that the average income for fulltime workers in Australia rose just 2.22% to $78,832 over the past year.

NAB said it took into account “a range of economic factors” and market indicators to determine risks.

“We recognise that no two suburbs are the same, and there are some geographic areas across Australia which have been impacted by local economic conditions,” an NAB spokesperson said. “As a responsible lender, we adopt strategies in these geographic areas that seek to reduce the risk to our customers and our business.”

Jonathan Jessup, principal at Johnson Real Estate Chermside, attributed NAB’s decision to the recent boom in apartment developments. “But units and houses are still selling quite well,” Jessup said.

NAB’s September 2016 quarter list of suburbs where a 20% deposit is required include the following postcodes:

• 4000 (Brisbane City, Petrie Terrace, and Spring Hill)

• 4006 (Bowen Hills, Fortitude Valley, Herston, and Newstead)

• 4101 (Highgate Hill, South Brisbane, and West End)

• 4102 (Dutton Park and Woolloongabba)