Greens MLA Shane Rattenbury.

SUPPORT: the changes are backed by Shane Rattenbury. Photo: Jeffrey Chan

Canberra's builders have welcomed a forthcoming debate in the ACT Legislative Assembly about contentious new planning laws, which they believe will add tens of thousands of dollars to the price of a new home and make it harder to upgrade houses in older suburbs.

Draft Variation 306 to the Territory Plan, Canberra's key planing document, has been delayed after the ACT Liberals' move last week to disallow the legislation.

While this will trigger a debate in the Assembly in either April or May, the legislation is almost assured of being adopted, with the support of ACT Greens Shane Rattenbury.

Mr Rattenbury said the variation contained long-awaited improvements to residential and estate development codes.

"The changes in the Territory Plan are a culmination of years of work, stemming from the 2008 Labor-Greens parliamentary agreement, which required mandatory passive solar orientation and increased solar rights for residential homes and subdivisions,'' he said.

"Many of Canberra's existing suburbs were built long ago, without consideration of important design principles that allow for energy efficient homes and good public transport. Put simply, these changes will mean that new areas of Canberra are better designed, with attention given to issues such as solar orientation and sustainable transport,'' Mr Rattenbury said.

The Housing Industry Association's ACT division said the new rules were confusing, complicated and would cause extensive excavation of building blocks.

Master Builders Association ACT spokesman Jerry Howard said the debate was badly needed. ''This is the democratic process working as it was intended to, as this draft variation requires far more scrutiny.

''There's a disconnect between agencies within the government. They don't understand what the impacts of these rules are on the ground.''

He said the building sector would continue lobbying for ''sensible amendments to the proposals''.

''If, at the end of the day, we lose, that's fine; at least we've given it a fair crack,'' Mr Howard said.

Opposition planning spokesman Alistair Coe is on leave and the Liberals are not commenting on the variation.

Environment and Sustainable Development Minister Simon Corbell said the key to the new solar policies was to limit overshadowing of neighbouring blocks.

Mr Corbell said the new rules would encourage innovative and individual home design that contributed to the character of the suburb and provided a more appealing built form in the city.