Robert Jenrick, the secretary of state for housing, communities and local government was speaking at a Conservative Party Conference fringe event on Tuesday organised by the free market Institute of Economic Affairs think tank.
Planning asked Jenrick about the government's impending review of how PD rights have impacted on housing quality, which was announced by his predecessor James Brokenshire in the Spring Statement.
The Coalition government introduced PD rights for office-to-residential conversions and larger single-storey home extensions in 2013, both of which are considered by councils under a light-touch prior approval process.
Since then, a number of other PD rights for residential conversions have been introduced, including for agricultural and light industrial buildings.
Jenrick said: "It's difficult for me to tell you what we are going to conclude at the end of the piece of work that we've done.
"But it is very much looking at the first wave of permitted development, office-to-residential, and assessing the evidence.
"There are obviously examples of poorly-constructed homes that have come out of that, homes that are very small.
"There are even examples of homes without any windows or only [a] very small number. There are some very bad examples."
But Jenrick said the policy has also produced "many good examples" and it had helped "bring a large number of properties onto the market that just wouldn't have been there".
Commercial-to-residential PD rights, he said, "has brought over 20,000 additional properties into the marketplace and that's a really significant contribution to the homes we need to build".
He added that "lots of young people" might "choose to have a small home as their first property".
The review, Jenrick said, would "look at whether there is evidence on the material level of poor-quality properties", such as those not built to last and that "will cause problems for future generations".
On Monday, Jenrick announced that the government would push ahead with proposals to ease planning rules to allow the upwards extensions of properties and the demolition of commercial buildings to make way for new homes.
On the "freedom to demolish", Jenrick said the government has "learned from some of the concerns about the first permitted development by saying that's it's 'in principle'".
Permission in principle (PiP) was introduced via the Housing and Planning Act 2016, and aims to offer developers a fast-track route through planning for housing-led schemes.
It splits the permission process in two, allowing residential proposals to secure PiP first and achieve full consent later through a further technical details consent.
Ministers are "giving the freedom for a developer to demolish", said Jenrick, but applicants "will still have to work productively with the local community and authority as to what that replacement actually looks like".
Issues of quality, the size of homes, parking provision and the appearance of the facade, would be considered by authorities, he said.
Councils and communities would still have the power to "challenge" the replacement building, but the government does not want authorities "gumming up the system and unnecessarily preventing developments from happening", he added.
The MHCLG has said the department would "make more information" on the PD housing quality review "available later in the autumn".
On Monday, housing minister Esther McVey said the government would be "changing the rules" around PD rights for new housing to improve standards.