Unequal area facility layout problem (UA-FLP) is one of the active research areas in the manufacturing domain. UA-FLPs can be solved using various techniques such as exact and approximation methods. A problem arises when these methods are used for solving UA-FLPs which have additional empty spaces. Several researchers have proposed different methods to address this issue, but unfortunately their performances have not been compared. Therefore, this article is aimed to compare those techniques used for dealing with empty spaces in UA-FLPs. Since a fair comparison was expected, all the techniques were implemented along with ant system using slicing tree structure representation. They were tested using problem instances taken from the literature. In general, the results showed that the bounding curve is the most encouraging technique for dealing with empty spaces in UA-FLPs.