Subdividing

How can I know if a house can be left on a property when it is a duplex block  R20 maybe the house is too far back , hard to tell ,have taken measurements approx , and seems may only be just be allowing enough for the rear subdivide block to happen and keep existing house .
 Have asked the shire but they don't allow plans info to be released to a prospective buyer . maybe I should just not buy it as it is risky that subdivision cannot happen without a demolition .
It is in Wanneroo , Perth W.A . I have copy of the block plans purchased throuh RPDATA  .so have actual block dimensions
to help compare my rough tape measurements .  Any feed back appreciated.

If it is R20, then you need a minimum lot size of 450sqm and you must have at least 3m width to allow for an access leg.

You could always ask the agent for the information you are after or engage a town planner or surveyor to do preliminary work to get the facts and see if it will stack in your favour.

RHPlanning.com
Town Planning and Property Development (Western Australia)