Apartment Unit Calculator

Start with the site area and the FSR and height limit from your local environmental plan. Site area multiplied by FSR is the maximum gross floor area (GFA). That is the ceiling, but it is not always what you can build.

The calculator then asks whether the building fits. Height divided by 3.1 metres a floor (a 2.7 metre ADG ceiling plus the slab) gives the number of storeys. The ADG separation for that many storeys comes off the frontage and the depth, the front setback comes off the front, and the result is a buildable footprint. Footprint multiplied by storeys, less balconies and voids, is the GFA the site can actually hold. The smaller of the FSR limit and the envelope limit is your achieved GFA, and the calculator tells you which one is binding.

From there, net saleable area (typically 80 to 85 percent of GFA) is divided by your average apartment size to get the number of apartments. Apartment sizes start from the ADG minimums and scale with your mix. Car spaces follow from the parking rate, and the basement is priced per space. Revenue is the saleable area times your price per square metre, and the cost stack adds land, stamp duty, construction, consultants, contributions, contingency, selling costs, finance and GST. The result is net profit, return on cost, and the residual land value for your target return.

The Housing SEPP's in-fill affordable housing provisions give residential flat buildings and shop top housing extra floor space and height in return for affordable housing. The scale is simple: the affordable share of GFA is half the FSR bonus. Ten percent affordable earns a 20 percent bonus, twelve percent earns about 24, and fifteen percent earns the full 30 percent. The height bonus is the same percentage. The bonus is applied on top of the FSR and height your LEP already allows, including other bonuses, and it does not apply to commercial floor space.

The catch is the cost. The affordable apartments must be kept for at least 15 years and managed by a registered community housing provider, so they are worth less than market apartments. And the extra floor space only helps if it fits: on a site where the ADG envelope is already the limit, the bonus adds nothing. Turn the bonus on in the calculator and the comparison panel shows the extra floor space, the extra apartments and the change in profit against standard controls. Read the Department's page on in-fill affordable housing for the eligibility rules.

The Apartment Design Guide applies to apartment buildings of three or more storeys in NSW. The rules that most often cap yield are building separation, deep soil (7 percent of the site), communal open space (25 percent of the site), solar access (two hours of midwinter sun for 70 percent of apartments), cross ventilation (60 percent of apartments) and a limit of about eight apartments per lift core on each floor. The calculator applies separation directly, because it shapes the envelope, and shows the rest as design targets for the building it has sized.

These are targets to design to, not a compliance assessment. A real scheme also depends on orientation, neighbours, overshadowing, flooding, bushfire, heritage and the council's own DCP. Where you are inside the Low and Mid-Rise Housing policy areas, the non-discretionary standards can lift the FSR and height above your LEP, and the affordable housing bonus can then apply on top.