The solar laws, which came into effect in 2013, govern the building of all new homes and are designed to promote solar access while preventing the blocking of sun to neighbouring homes.

The housing and construction industry has blamed "Variation 306" rules on poor house design in new suburbs, particularly in knock-down rebuild projects and extensions in established areas.

The ACT government has flagged that it wants to rezone and sub-divide all Mr Fluffy blocks of more than 700 square metres – about 771 of the 1021 affected properties.

Chief Minister Katy Gallagher expects to net an extra $90 million or $100 million through the re-zoning, but the government will still be at least $300 million to $400 million out of pocket at the end of the scheme.

Australian Property Institute ACT president Paul Powderly said chopping Mr Fluffy blocks in half to build a home on each wouldn't work in the majority of cases under the solar rules.

"The current blocks are not designed in a sense that they're the right shape to be cut in two," he said.

"Variation 306 will certainly govern a lot of the blocks; a lot won't be able to be sub-divided."

Mr Powderly, who is heading the valuations side of the buyback scheme, said the only way to be able to build on the blocks would be to unit title them.

But he said this would require a change to the unit titles act and the solar access rules, while slightly more flexible, would still apply.

"It has a bigger impact on smaller blocks and that's why if you're starting to cut up blocks that weren't designed to be cut up then you're going to run into that issue," Mr Powderly said.

He will write to the ACT government this week about the issue and other problems that had arisen in the first week of valuations, including how the blocks will be valued after remediation.

Master Builders Association of the ACT deputy executive director Jerry Howard said the association had lobbied strongly against the solar rules applying to established suburbs because of the problems with block orientation.

"If you build in a greenfields development then the block orientations are already adjusted to get the best possible solar access," he said.

"But a lot of these houses were built at a time when block orientation wasn't really given any serious consideration."

He said to comply with the rules homes had to be built into the ground so they were beneath the solar envelope.

"It's just giving some really bad outcomes and this will be no different," Mr Howard said.

He said the stringent solar rules could affect the salability of the sub-divided blocks after remediation as it would limit what could be built and make projects more expensive.

Architect and Housing Industry Association vice-president Glen Dowse said only corner blocks should be considered for sub-division because there would be dual street frontage.

He said splitting many standard residential blocks would leave them "almost undevelopable" particularly when trying to maximise the size of the home and meet the solar access requirements.

"In the short term these people are going to have a lot of pain when they try to meet these rules," Mr Dowse said.