They believe a new planning variation replacing two previous changes dumped by the ACT Government has led to odd shaped homes, tiny single rooms, huge excavations, flooding, steep driveways and homes chopped off to meet setback rules.

When housing spreads into Molonglo's steeper slopes, the problems will worsen.

An architect among industry representatives trying to fix the problem for more than two years, Glen Dowse, is appalled at what is confronting builders and owners of new homes.

"Those people are having a go, doing the best they can with what they've got," he said.

"And they are expensive blocks of land, you are paying $100,000, $150,000 more for a house at Wright than you are at Gungahlin."

Mr Dowse said the changes stemmed from the previous Labor-Greens alliance and the current Government's reluctance to adjust rules, mainly on solar access.

He said shortcomings were put forcefully to the planning authority last Friday, including the fact changes were made as late as February 22.

Mr Dowse said the planning authority didn't appreciate architects could not apply the new codes in residential zones near shops (RZ2) because they were unsure of what they were.

"The impact is pretty major in all the other zones and in RZ 2. My response was, there was no way as a responsible designer we would design to that code until we knew what the final make up of it was."

ACT Master Builders Association spokesman Jerry Howard said outcomes at Wright, the first suburb to adopt the new rules, were horrendous.

When applied later to older suburbs, the solar access rules would restrict extensions and additions.

Draft Variation 306 to the ACT's key planning document, the Territory Plan, passes its disallowance period on Thursday.

"It is the most complex, confusing thing on earth.

"When they (the planning authority) see the results on the ground, we'll spend another two years trying to iron all this out."

Building Designers Association ACT region president Adam Hobill said the variation did not mean mere tinkering.

"It is whole lumps of houses that need to get chopped off.

"The amount of time they (ACT Government) have had to consider this variation and amount of industry feedback they have had, they would have to know these are the implications it is going to have."

Industry spokesmen say aspects of DV 306 are a step forward, but warn people who have bought small blocks of land will not fit their new homes on them because of solar access rules.

Major impacts will be felt in all residential zones on units and homes in brownfield and greenfield areas.

Environment and Sustainable Development Minister Simon Corbell said the legislation would be applied to development application at some point, after previous ones "prepared in good faith under the previous rules " had been approved under the old rules.

Mr Corbell said solar access rules gave people buying land confidence their access to sunlight would not be compromised by their northern neighbour.

He said his department would monitor the new rules, which had so far attracted wide community support.