New minimum apartment sizes introduced by the Environment Minister Alan Kelly last month cannot actually be built, according to the Royal Institute of the Architects of Ireland.
The body says the smallest permissible rooms would not fit inside.
In December, Minister Kelly issued the new planning and design guidelines which reduced the overall size of one-, two- and three-bedroom apartments.
However, they did not cut the minimum size of bedrooms, living rooms and kitchens.
RIAI Vice President and Housing Spokesman John O'Mahoney, says the anomaly probably occurred because the new regulations were not road-tested.
He said: "If you take all these and you blend them together in the design of an apartment, what we are finding is that the space, the minimum floor areas don't work. In fact they are 10% bigger.
"I think it may be unintended consequences. The regulations came out in 2007 and then we crashed, and so we never really had a chance to road-test them.
"I suspect that had they been road-tested, this little anomaly would have come to light."