Forsyth Barr broker Suzanne Kinnaird said Chorus' guidance as to what it cost to actually connect homes to fibre would be at the upper end of the guidance range of $900 to $1100 per premises in 2011 dollars.
The guidance update reflected a combination of tight labour supply, faster take-up of services, quality pressures and Chorus' experience as it increased its focus on hard-to-connect homes.
''While Chorus is well progressed on its communal down-the-street build, it is in the early stages of its connection programme.''
Forsyth Barr had increased its connection costs forecast to $1000, nearly at the $1100 top range, she said.
Chorus had been deferring many of the hard-to-connect homes, while it waited on consents and other issues, and the increasing visibility around the quality of connections.
''We believe there is a risk of further cost surprises and the top end of that guidance range is the appropriate point to use rather than the midpoint.''
Chorus was also assessing its capitalisation policies in relation to fibre-related activities, Ms Kinnaird said.
There were at present activities supporting fibre connections it had previously expensed. It had noted other local fibre companies (LFCs) capitalised those costs and as part of a review, due to changes in accounting standards, it would consider its treatment of some of those costs.
Chorus had noted the impact in any given year would not be material although any change in capitalisation policy would increase future asset base values, which was positive, she said.
Higher-than-anticipated demand for fibre was increasing costs for Chorus.
While Chorus' future was fibre, its revenues remained heavily dependent upon its copper network.
''The signal today is Chorus expects this higher level of demand for fibre to continue for longer. In our view, this means losses of copper lines in those other LFC areas will also be higher over time.''
Forsyth Barr assumed by 2025, 90% of residential premises able to get fibre would do so, up from 85%. That reduced the valuation of Chorus by 20c per share, Ms Kinnaird said.
Forsyth Barr's share target price had fallen to $3.90 from $4.30. The shares last traded at $3.73.
