"domestic garages where the floor is suspended" - are garages attached to houses in the UK not on grade?

He’s talking about both domestic (individual) homes and multi storey parking structures. The structural codes in the UK have a specified design load for cars per meter squared, for the pedantic this is contained in the UK NA of EC1 and there is further guidance by IStructE (institute of structural engineers). This load value is the same irrespective of the building type in general terms. The load value used was set many, many years ago before EV’s or for that matter massive SUV’s became a thing. Technically modern SUV’s and large EV’s cars are heavier than the design load value. Safety factors and low probably of full occupancy with such heavy cars means that multi-storey parking structures are likely to be okay in reality. Recent IStructE guidance recommends a higher value be used for new designs. Individual dwellings with garages will have the foundations formed as either a ground bearing slab or some form of suspended construction. The ground conditions determine which is appropriate. Sloped sites or ground that comprises strinkable soils being the most common reason for suspended slab construction. There is a theoretical risk that a suspended domestic garage floor if designed down to just the code value plus safety factors could collapse due to overload with such cars. There is also a risk that ground bearing slabs could fail for the same reason (overload). The risks are very low due to construction practices adopted and the ultimate capacity of floor planks or beams used with suspended floor construction. In the USA many states require something called the international building code (IBC) to be followed. Even though the title has the word international it is bizarrely a US standard not an international one. IBC has a similar issue with design code load values for car parking per square foot being old and somewhat light vs the weight modern trucks, SUV’s and EV’s. Under designed parking structures is a bigger issue in the USA than the UK due to a much larger difference between code and reality particularly for garages both domestic and communal designed before 2006.