Utilising equity in an investment property to assist a home purchase

Looking at building a new home within the next 6-12mnth(have engaged an architect).

The new home may cost $500,000 to build.

–– Have an investment property loan for $20,000 and property worth $300,000)

What I would like to know, am I able to access the equity in our Investment Property to assist with the new home cost?

For example, increase the investment loan from the present $20,000 to $200,000 and the $180,000 made available from this can be put against my eventual increased home loan.  

For ATO are we able to realise equity in our investment property to assist in what I have described above and still negative gear the property at the new amount.

Thanks in advance for any suggestions.