Does the age of the existing house affect a dual-occupancy application?

Generally, no. The age of the existing house by itself does not determine whether a dual occupancy can be approved. The application is assessed against the current planning requirements applying to the block and proposed development.

The ACT Missing Middle Housing Design Guide specifically illustrates a detached dual occupancy that retains the existing dwelling, showing that retaining an older/existing house is contemplated.

However, the age of the house may become relevant if it has heritage protection or other site-specific constraints. Heritage requirements can affect alterations, additions, new buildings, demolition, landscaping, site coverage and setbacks.

Reference: ACT Missing Middle Housing Design Guide - ACT Missing Middle Housing Design Guide