The government this month said more than 8000 New Zealand homes had been retrofitted in the first eight weeks of its Heat Smart insulation scheme.
Mr Scott declined to name the businesses or products he was concerned about, but said he did not believe they were Heat Smart-registered providers.
While it was good more homes were being insulated, Mr Scott, who has 30 years' building experience and is a former registered Master Builder, said he had become concerned after conversations with several homeowners, most of them elderly, who had agreed to insulation that he considered might not be effective or might even damage their houses.
"There are some legitimate concerns I have as a builder about some insulation products," Mr Scott said.
"Elderly people should be able to get good advice rather than grief and huge expense later on."
He said there were some basic questions homeowners should ask before they retrofitted insulation.
"Has the product been Branz-tested?" he asked.
"Does it have adverse effects on electrical wiring and cables?"How durable is the product?"Will moisture be added to the timber framing during installation? "What happens if the air cavity is blocked?"Is it fireproof? Under the Building Code, you are not allowed to cover downlights because the heat can build up and cause a fire.
"What happens to their insurance if it's installed by someone who is not an approved installer?"Mr Scott said homeowners should check with the Dunedin City Council before retrofitting insulation to see whether a building consent was required.
"People should take all manufacturers' claims that aren't independently verified with a grain of salt.
"I think people can be swayed by advertising images and guarantees offered. They should check and then check again before going ahead with a product."
Dunedin City Council chief building control officer Neil McLeod said he believed some insulation retrofitted to housing was building work and so required a building consent.
Dunedin City Council energy manager Neville Auton said the Heat Smart scheme had "checks and audits" to help ensure insulation was installed properly and would be effective.
Insulation installers did not have a members' association such as the Master Builders to help ensure the quality of the industry, Mr Auton said.
"So there can be some cowboys out there," he said.
