How are base buildings emissions calculated?

This article summarises the key parameters used in the model to calculate emissions from base buildings.

Base Buildings
Base building energy consumption occurs in the shared spaces of office buildings and includes energy consumed for the operation of lifts, lighting in lobby's, equipment, hot water, and building heating and cooling. Base building energy consumption is in addition to electricity used in an office space. Generally, tenants will only pay for the electricity consumed within the office area that they occupy.  

The proportion of electricity, natural gas, and diesel attributed from base building energy to your organisation is calculated using the building NABERS Rating, your net lettable area, and the hours per week your office is occupied greater than 20%. 

The Calculation Method (Australia) 
Base building emissions are calculated using a model developed by the National Australian Built Environment Rating System (NABERS). NABERS measures the environmental performance of existing buildings using actual building data.
The NABERS rating system for base buildings measures building performance on a six-star scale. Zero stars indicates that a building is performing below average and has lots of scope for improvements. A six star rating indicates that the building is leading in its performance. NABERS ratings for buildings in Australia can be found here
The Calculation Method (International)
The average energy intensity of buildings (measured in MJ/m2) is used to determine base building emissions for international offices. Standard values have been used depending on the overall energy efficiency of the building occupied. Base building energy consumption is dependent on the floor area occupied by your organisation.