This decision may be made for you depending on how you wish to lay the oak flooring. If you have underfloor heating or want to float your floor over an underlay, engineered hardwood is the way to go. The kind and thickness of the flooring are sometimes determined by the subfloor. If you have joists, for example, your wooden flooring must be at least 18mm thick. For more details, take a look at How to Install Wood Flooring on Different Subfloors.