According to the DOE’s Office of Energy Efficiency & Renewable Energy, nearly two-thirds (63%) of all U.S. households have a garage or carport available to them (and often with electricity already wired in).
Ford C-Max Energi
In other words, those 63% who own a parking space, in theory, could equip an EVSE charging unit for a future plug-in vehicle purchase.
And the ratio is higher for new household occupancy builds - 71%.
As the plug-in vehicle market in the US barely exceeds 1% for most months (unless you are talking about the recent, and very impressive, 1.47% gain in December), the lack of a garage or carport certainly won't limit sales in the near term - it could encourage them; although we have to note that plugging in is still a significant hurdle for a fair chunk of the population at large..
"According to the newly released 2015 American Housing Survey, 63% of all occupied housing units have a garage or carport. Garages and carports often have access to electricity for parked vehicles, so these data are important for electric vehicle market analysis. Seventy-percent of new construction units (five years old or less) have a garage or carport. The West and Midwest regions of the country have a greater percentage of housing with garages or carports, each with over 70%. For rental housing units, only 37% have a garage/carport, as compared to 78% for those owning housing units."
Share of Housing Units with Garage or Carport, 2015
Share of Occupied Housing Units Percent with a Garage or Carport Tenure Owner 63% 78% Renter 37% 37% Location - Census Region Northeast 18% 49% Midwest 22% 72% South 37% 56% West 22% 76% Age of Housing Unit New construction (< = 5 years) 3% 71% Older than 5 years 97% 63% All Occupied Units Total 118,290 units 63% Source: U.S. Bureau of the Census, 2015 American Housing Survey, AHS Table Creator, Accessed December 2, 2016.