in the USA are likely to call it a parking structure since their work is all about structures and since that term is the vernacular in the United States. When constructed as the base of a high-rise, it is sometimes called a parking podium. United States building codes use the term open parking garage to refer to a structure designed for car storage that has openings along at least 40% of the perimeter, as opposed to an enclosed parking garage that requires mechanical ventilation. Natural or mechanical ventilation provides fresh air flow to disperse car exhaust in normal conditions, or hot gas and smoke in case of fire. Typically parking consultants in the UK describe the number of car park floors in terms of "G+x". G stands for ground and x for the number of floors above ground. For example, G+5 is a multi-story car park structure with a ground floor and 5 floors above that, i.e. a total of 6 floors. The preceding does not apply to the United States where B+x refers to basement levels ascending in number x while descending in elevation, L1 or ground level [unlike European standards where ground level is below Level 1] with added levels as L2, etc. Construction types Concrete Steel structure Automated (mechanical) Steel structure Structure car parks are car parks made of structural steel components connected to each other to carry the loads and provide full structural rigidity. Steel is a high-strength material requiring less material than other types of structures like concrete and timber. Steel construction features: Cost savings: inexpensive to manufacture and erect, and requires less maintenance than traditional building methods. Speed: Allows construction/prefabrication off-site with rapid installation on-site. Some suppliers claim construction in days. Durability: Suppliers claim 50-plus years lifespan. Removability: Steel car park structure could be designed to be removed at a later date. Expandability: Steel car park structures can be expanded easily at a later date. Creativity: Steel allows for long column-free spans. The ceiling slab of the steel structure car park is typically made of composite material such as corrugated steel sheets and concrete. The surface of the first-floor parking can be left bare or covered with epoxy or tarmac. Foundationless and modular Demand, steel features, and innovation have led to the development of a foundationless, modular, removable steel car park structure. Parking demand often grows quickly, significantly and sometimes unexpectedly. Modular steel car