The Department of the Enviroment has described as "disingenuous and inaccurate" comments made by the RIAI about new apartment size guidelines.
In a statement, the department said the new apartment guidelines are designed to match affordability levels under the new mortgage lending rules.
It said the guidelines are "minimum quality standards...rather than a template for the roll out of minimum standard apartments."
Earlier, the Royal Institute of the Architects of Ireland said that the new minimum apartment sizes proposed by the department cannot be built.
Smaller apartments were to be permitted under new planning guidelines published by the department in December last year.
The guidelines on design standards for apartments set the minimum size of one-bedroom units at 45 sq.m, two beds at 73 sq.m and three beds at 90 sq.m.
Speaking on RTÉ's Morning Ireland, RIAI Vice President John O'Mahony said plans by Minister for Environment Alan Kelly to reduce the overall size of one, two and three bed apartments was not possible.
He said this was because regulations include minimum floor areas but also include minimum sizes for living rooms, dining rooms etc.
Mr O’Mahony said when these are combined they generally work out at around 10% larger than the sizes specified.
He said there is an idea that storage can be put in the basement, but effectively storage should be provided with the units.
He added that in many places storage cannot be put in the basement.
Mr O'Mahony said the RIAI tested the new plans when they were outlined and when it applied the new guidelines, they could not make them work.
Speaking on RTÉ's News at One, Dr Lorcan Sirr, from the School of Real Estate and Construction at Dublin Institute of Technology echoed Mr O'Mahony's comments, saying the new rules for smaller apartments would be like "trying to put a round peg into a square hole."
Dr Sirr said the Department of the Environment has managed to create mandatory rules for the construction and development industry where A does not go into B.
He said the Department has not released any research underpinning its rules and he questioned whether there was "any decent research underpinning this".