Architectural Ecology will undertake a detailed costing of building the library as a second extension to the Waitati Hall, rather than demolishing the existing library and rebuilding there.
Deputy chairwoman Geraldine Tait, who opposes demolition, said she was pleased but had little hope of a change, as the architect's preference was the status quo.
At Wednesday night's board meeting, a petition containing about 80 local residents' signatures was presented.
Opponents want the existing library, which is just 18 years old, to be retained as a community meeting room.
Architect Tim Heath said he believed the investigation would show the present plan, with a price tag of about $850,000, was the cheapest.
If converted to a community facility, the library would need extra work to bring it up to standard, and building on the south side would mean altering the hall, entailing extra cost.
However, the architects were approaching the costing request with the utmost professional integrity, and would not advocate an option unless it was the best one for the community.
The new facility, to be built on the existing north-facing site, is to use natural lighting, solar glazing, ventilation and insulation to make it energy-efficient.
Community board chairman Alasdair Morrison said the delay was not holding up construction, which was some time away yet.
The community needs to raise about $350,000 for the library, for which the Dunedin City Council has pledged $500,000.
Waitati resident Rosemary Penwarden was pleased the community board had not "rubber-stamped" the plan at Wednesday's "intense" meeting.
She believed some community board members initially underestimated the strength of feeling on the issue.
Ms Penwarden was keeping an open mind about the proposal, and was open to changing her stance if she could be shown why getting rid of the existing library was the better option.
