Housing New Zealand has been retro-fitting for 13 years but can't say how many of its 70,000 homes are still uninsulated in cold zones like Canterbury.
This was despite the Government spending $30 million on its Energy Efficiency Retrofit programme in the past six years.
Housing New Zealand (HNZ) is the country's biggest owner and manager of homes but by one new estimate New Zealand still needs modern insulation for half a million houses.
The retrofit is aimed at all its properties built before 2000, when a modern building code raised home insulation standards.
A total 48,030 properties had been insulated "wherever practicable" at December 31, 2013, HNZ said. But the agency couldn't say how many of its homes were still uninsulated, including Christchurch where its stock had been laid bare by the earthquakes.
"The way we have collected information throughout the lifetime of this programme means Housing New Zealand does not hold a central record of uninsulated properties - instead this data is in some cases held on individual files," general manager of property services Marcus Bosch said.
HNZ did have "numerous databases that we check manually, and we also have information obtained from regional teams", he said.
This information had been audited during the 14-year lifecycle of the programme.
Some HNZ properties built before 2000 could not be insulated because of their construction or design. Apartment units might be within a complex, have concrete floors or inaccessible floor and roof cavities, Bosch said.
In May last year Housing Minister Nick Smith announced a "Warrant of Fitness" applying to the 69,000 HNZ properties.
The warrant, one of the recommendations of an expert advisory panel on child poverty, was to complement the government project that had insulated about 215,000 homes since 2009.
Smith expected that by this year HNZ would have insulated "all of its homes capable" of being either retrofitted or modernised.
The Green Party had since asked Smith how many homes the Government was not able to insulate by the end of 2013, given his pledge to insulate every state house possible.
Just over 48,000 homes had been insulated under the retrofit programme but some properties couldn't be upgraded because of their design, he replied to written questions.
HNZ had advised that in these cases it provided "other energy efficient interventions" such as improved heating, fixing draughts, and insulating hot water and pipes.
Since the 2008/09 financial year the agency had spent $30m on the retrofit. This included a "source of heating" in about 10,000 homes, including heat pumps, log fires, electric heaters and closing off fireplaces, Smith said.
Community Energy Action (CEA) chief executive Caroline Shone estimated half a million homes still needed insulation.
A range of insulation providers had insulated about 250,000 houses through insulation schemes, including CEA which had insulated more than 20,000 homes during 20 years.
Owners or managers of homes built before the turn of the century should be aware the property's insulation may need "topping up or a complete upgrade", Shone said.
- The Press