# Dual occupancy

If you are building one new dwelling on a site with an existing dwelling (creating a dual occupancy arrangement):

• In the "Start new project" popup, select "1 dwelling"
• If the dwelling has shared facilities (such as a shared garden, rainwater tank, swimming pool, etc), refer to the apportionment guidelines below to determine the apportionment of these shared facilities.

If you are building two new dwellings:

• In the "Start new project" popup, select "more than 1 dwelling"
• Enter the details of all your shared facilities as common areas and central systems

### Apportionment guidelines

This guideline will help you to complete a BASIX assessment using the BASIX tool if the dwelling for which you are completing a BASIX assessment is part of a dual occupancy arrangement. The guideline applies to attached or detached dual occupancy dwellings that share the same site.

### Determining the inputs for your dual occupancy BASIX assessments

If the dwellings share any of the following:

• landscaping
• rainwater tank
• stormwater tank
• swimming pool or spa
• alternative energy supply

it is necessary to apportion these shared features before you enter inputs, that is details, for each dwelling into BASIX. This is done by selecting the appropriate INPUT FACTOR from Table 1 below and multiplying this by the area, volume or power supply of the item to determine the value to be entered for that item in BASIX. An example is given on the next page. The figures at the end of this guideline illustrate scenarios related to shared and separate roof and landscaped areas.

Input factors for selected bedroom numbers

### Example

You are proposing a dual occupancy consisting of a 3-bedroom dwelling (Dwelling 1) and a 4- bedroom dwelling (Dwelling 2) with a shared 7000-litre rainwater tank.

• The INPUT FACTOR for Dwelling 1 = 0.44
• The INPUT FACTOR for Dwelling 2 = 0.56
• The rainwater tank volume for Dwelling 1 = 0.44 x 7000 = 3080 litres
• The rainwater tank volume for Dwelling 2 = 0.56 x 7000 = 3920 litres

Page of BASIX toolTopic on pageWhat applicant needs to enter
Project details Site area Enter the site area of the whole site
Project details Roof area 1. If the dwellings do not share any roof area, enter the roof area of each separate dwelling. (See Figure 1.)
2. If the dwellings share a roof area, add the shared or common roof area (eg. garage roof areas) to the roof area of each separate dwelling. (See Figure 2.)
3. Enter each calculated roof area into the BASIX tool for each separate dwelling.
Landscaping Landscaping 1. If the dwellings do not share any landscape area, enter the total area of vegetation and area of indigenous species of each separate dwelling. (See Figure 3.)
2. If the dwellings share a landscape area, multiply the shared landscaped areas by the appropriate INPUT FACTOR from Table 1. (See Figure 4.)
3. Enter each calculated total area of vegetation and area of indigenous species area into the BASIX tool for each separate dwelling.
Stormwater Rainwater tank 1. If the dwellings do not share a rainwater tank, enter the individual roof areas that collect water for each rainwater tank and the rainwater tank size of each tank for each separate dwelling.
2. If the dwellings share a rainwater tank:
a) Multiply the roof that collects rainwater for the rainwater tank by the appropriate INPUT FACTOR from table 1.
b) Multiply the rainwater tank size by the appropriate INPUT FACTOR from table 1.
c) Enter each calculated roof area and rainwater tank size into the BASIX tool for each separate dwelling.
Stormwater Stormwater
tank
1. If the dwellings do not share a stormwater tank, enter the individual run-off areas (roof area, impervious area, landscape area) that collect water for the stormwater tank and the stormwater tank size of each tank for each separate dwelling.
2. If the dwellings share a storm water tank:
a) Multiply the runoff-areas (roof area, impervious area, landscape area) that collect storm water for the storm water tank by the appropriate INPUT FACTOR from Table 1.
b) Multiply the stormwater tank size by the appropriate INPUT FACTOR from Table 1.
c) Enter each calculated runoff area and stormwater tank size into the BASIX tool for each separate dwelling.
Stormwater Swimming pool & spa 1. If the dwellings share a swimming pool or spa, multiply the
volume of the swimming pool or he spa by the appropriate
INPUT FACTOR from Table 1.
2. Enter the calculated volume of the swimming pool or spa
into the BASIX tool for each separate dwelling.
Thermal comfort

Each dwelling can be separately described in Thermal
Comfort without using any INPUT FACTOR

Energy Hotwater system

If sharing a hot water system, both dwellings must enter the
type of hot water system separately.

Energy Swimming pool & spa

If sharing a swimming pool and/or spa, both dwellings must
heating separately.

Energy Alternative energy supply

1. If the dwellings share a photovoltaic (PV) system, multiply
the kW of the PV system by the appropriate INPUT
FACTOR from Table 1.
2. Enter the calculated kW of the PV system into the BASIX
tool for each separate dwelling.

 Figure 2 - dwellings share roof Figure 1 - dwellings do not share roof
 Figure 3 - dwellings do not share landscape Figure 4 - dwellings share landscape