The changes have reintroduced the site area per dwelling calculation, which will reduce the number of apartments that can be built on blocks zoned R30 and R35.
Parking will also be increased to ensure every apartment is allocated at least one bay.
"It will have clear benefits for people, especially in the Mt Hawthorn area," Mr Carey said.
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READ NOW"It does apply to nearly all of Mt Hawthorn, we welcome it. We are still likely to continue with our ban on multiple dwelling in Mt Hawthorn."
The City of Vincent's Town Planning Scheme amendment to ban multiple dwellings in Mt Hawthorn was passed at council and is yet to be approved by the WA Planning Commission.
Planning Minister John Day said the R-Code changes were in response to community and local government feedback.
"The R-Codes and local government planning schemes govern what can and can't be built on a residential block of land," Mr Day said.
"Since 2010, the number of apartments allowed on a block has been subject to a different calculation (plot ratio) to other infill developments such as units or townhouses.
"This has seen an increase in apartments being built in established suburbs with predominantly single homes."
R40 blocks remain the same.