NBN Co will take around 1.2 million premises out of the hybrid-fibre coaxial (HFC) footprint and move them to its fibre-to-the-node network in an effort to reduce its costs.

The network builder today revealed its new three-year corporate plan, its first to outline the rollout to expected completion in 2020.

In a marked change from previous plans, the new document reveals the HFC footprint will be cut back from a previous estimated 4 million premises to between 2.5 million and 3.2 million, with an expected final number of 2.8 million.

The 1.2 million premises to be taken out of the HFC rollout will be moved into the FTTN footprint, served either by a node, fibre-to-the-basement (FTTB), or the currently under testing fibre-to-the-distribution point (FTTdp).

It gives the combined FTTN footprint a premise count of between 5.1 million and 6.5 million, the vast majority of the total 11.9 million-premise network.

NBN Co CEO Bill Morrow said the network builder had gained greater insight into the state of its acquired Telstra and Optus HFC networks throughout the year, allowing it to make more detailed planning decisions.

"[Last year] we didn't have contracts in place with equipment suppliers and delivery partners .. and we lacked a lot of the data associated with exchange information from Telstra and Optus. We've been able to close all of that out through the year," Morrow said.

"The data that is available today changed the type of technology we should choose."

That technology allocation would likely change further as NBN Co accesses more detailed network information, the new corporate plan indicated.

NBN Co expects the cost per FTTN and HFC premise to both sit at $2300.

It had previously estimated the HFC cost per premise to be $1800, but revised that figure up this year due to "further understanding of of network planning and design" as well as the move to DOCSIS 3.1 and to a demand drop to build drop model for lead-ins.

Cost per brownfields FTTP premise is $4400 and $2100 for greenfields. Fixed wireless cost per premise is $4600, NBN Co said.

The cost per greenfields FTTP fell from $2600 thanks to the introduction of things like skinny fibre.

Time running out for extra funding

NBN Co is still yet to detail concrete plans to access more funding despite having only 12 months before its current pool of funds runs out.

The network builder will reach its $29.5 billion peak government funding cap before the end of its curent FY17 financial year.

It is expecting the rollout to cost at least $49 billion by 2020, but is planning for a maximum of $54 billion. Its latest corporate plan has revised down the peak funding amount from a previous estimated $56 billion to $54 billion.

When the current funding pool runs out at the end of FY17, NBN Co will need to raise around $10 billion within 12 months to meet its expected requirement of of $39.5 billion in funding for FY18.

Morrow today would only say that the network builder was in the process of securing external debt "as we speak right now".

"We are confident we'll be able to obtain the necessary funds," Morrow said.

"It's still in progress. We've already contacted the credit rating agencies, which is naturally the first step in raising any sort of debt. That process is underway at the moment."