Housing is defined as the part of the settlement, the housing facilities, where the people have their personal space, be they apartments or the equivalent of actual houses. It is different from lodging facilities where the occupants are expected to be transient.
On Mars, housing needs to provide a breathable atmosphere, protection from radiation and a comfortable environment. It may have external windows, but these need to be designed in a way that prevents excessive radiation exposure. Artificial lighting is likely to be standard. It might be possible for the housing to be open on interior parks, for a more open plan.
Housing may come from Earth in the form of modules that can be assembled together with other elements to create a settlement, or built on site with in-situ resources.
Minimum living space for housing depends partly on cultural elements, but varies from a minimum of about 10 m2 per person to a comfortable 40m2 per person in most of Europe and 60-70m2 per person in the US and Canada. With a height of 2,3m, this corresponds to volumes of 23, 92, 140 and 160 m3.
NASA has explored the minimum volumes required for long term stays in space. The minimum volume was set at 25m3 per person for a maximum of 912 days. This includes a personal space of 5m3 per astronaut. Space can be used much more effectively in the microgravity environment of a space mission, and these values would be unacceptable for Martian housing. The value of 40m2 might be a fair compromise for settlers, 30m2 or less might apply to visitors, or to an scientific base rather than a settlement. This would include circulation spaces and some common semi private areas, but not services, work leisure, public spaces or production areas.
Housing needs to include systems for heating, cooling, ventilation, air filtration and humidity control. Materials used in construction need to reduce noise and the external walls need to stand up to the interior air pressure.
Lighting levels of common areas may need to be higher than usually provided on Earth, as the common areas may serve as a kind of outdoors and therefore need to provide a lot of contrast with the private spaces. Lighting simulating the outdoors may be up to 100 times more powerful than regular interior lighting, requiring up to 130 W/m2 or more, rather than the usual 1 to 1,5 W/m2 used in building lighting.
Furniture, surface finishes, partitions, personal storage and interior systems add considerably to the mass of the housing areas. Probably the heaviest element of construction will be radiation shielding. This will be one of the prime use of in-situ resources, as martian regolith or ice can serve the purpose adequately. Again, a short term stay scientific base could afford to use less shielding, but a settlement will require massive protection to reduce the radiation levels to acceptable levels for a lifetime of residence.