Generally, I like this a lot. The key is that for it to work, you must build taller, but it doesn't have to be all that tall. I've lived in several places that had great walkability, and they all had one thing in common: They were built before the invention of the automobile.
The best for walkability was Berlin, which, in the inner part, is mostly 5-6 story buildings. Within two blocks there were numerous stores and about 8 restaurants and a few bars. I also lived in an older suburb of mostly single family houses, but the lots weren't that big, and every house was two stories.
The key to walkability is that you need density. For a business to get much foot traffic, you need a good population in the walkable catchment area, and for that you need density. To get density, you need to build up. Unfortunately, building up is more expensive. Another thing that's helpful is alleys. If you put the garage behind the house, you don't need as much frontage width for driveways and garage doors.
I’m not sure about your argument of “you have to build up”. Lot of places in Europe have strict limits regarding how high a building can be and they do have lot of small stores around, Berlin, that you mentioned, is very strict on this. A few examples: Hamburg residential areas seem to have ~4-5 floors max. Groningen has neighborhoods where apartment building are limited to only 2 floors (So just two apartments). They both have enough density to have small businesses around.
Maybe I’m misunderstanding the US situation you’re comparing to, and people there just build flat, so even a few floors is already building up? That would be strange though...
A very large portion of houses built in the past 70 years in the U.S. are single story. My point was that even going from single story, single family housing to two story, single family housing makes a big difference in density, and that can enable walkability.
I specifically don't mean that you have to build up to Manhattan levels to get walkability. Personally, I find the skyscraper jungle of Manhattan to be a nice place to visit, but I wouldn't want to live there, at least at my stage in life.
If anything, perhaps Manhattan levels of density are not great for nice retail businesses. If the average building is 8-10 stories, there is relatively little ground level space available, rents are high, and so there is little room for experimentation. The 5-6 story Berlin (and to some degree Paris) level of density is maybe a sweet spot.
Now, this doesn't necessarily work as well for families with children. However, Berlin manages to be decent for this by having very wide sidewalks, a lot of parks, and hinterhofen. Some parts of Chicago and Brooklyn manage to achieve a similar effect with single family housing by having tightly spaced three story row houses.
Like I said, ultimately a lot of cities that are nice to live in in this way are that way because they were built before the invention of the car, so people valued this much more than they do today when the alternative is to get in their car and go to some big box store with a huge parking lot that doesn't need to be very near by.
~4-5 stories is totally sufficient to be "dense" compared to most of the US. Cities in the US sprawl absurdly flat. Consider that Paris is one of the densest cities in the world, and famously has almost no tall buildings.
By curiosity I checked some numbers to compare. Paris density is just crazy! When compared, Berlin (mentioned by cameldrv) really has a low density for the huge capital it is, at around ~3.9k persons/km². London seems to have around 5.5k, New York around 10.2k, while Paris is at a crazy 20.7k!
It's a bit exaggerated because Paris proper is only a small part of the urban region. It's more appropriate to compare Paris to Manhattan. Both house around 2 million people at 20k people/km², and both are in sprawling metropolitan areas of 10-20 million depending where you stop counting.
As dmurray commented there's differences in what is counted. Another difference is that Paris proper has relatively small parks, whereas Berlin has several huge ones as well as lakes.
So yeah, Paris is dense, but if you compare block by block the differences are smaller.
Even the (by far) most dense borough of Berlin is only at 14,373/km²[1], though. That's considerably lower than almost all of the Parisian boroughs[2]. Even the whole city's average is 20,000/km². From the point of view of most American cities with some obvious exceptions, the difference is probably indeed not that noticeable though.
Single family detached housing on fully separated lots of 1-2 storeys, and very often only a ground floor, is typical through much of the US. That describes a startlingly large fraction of San Francisco, and even larger "dense" neighbourhoods (Richmond, Sunset) are typically 2-3 floors, where ground level is garage parking ("soft story" construction, a major earthquake concern. Only in NYC and environs do you find generally denser construction.
A 5-6 storey standard would likely more thaan double SF's housing capaacity.
I don't think I've seen a reasonably modern building around here (Vancouver, Canada) over 2 floors without an elevator. I expect we have accessibility rules that require them for anything other than individual private residences.
5 floors is also about the limit for wood frame construction, you need a more expensive building style to go higher. Obviously consult a civil engineer for details.
What this means in practice is you don't build between 6 and 10 floor buildings because the numbers won't work out. (obviously there are exceptions)
The best for walkability was Berlin, which, in the inner part, is mostly 5-6 story buildings. Within two blocks there were numerous stores and about 8 restaurants and a few bars. I also lived in an older suburb of mostly single family houses, but the lots weren't that big, and every house was two stories.
The key to walkability is that you need density. For a business to get much foot traffic, you need a good population in the walkable catchment area, and for that you need density. To get density, you need to build up. Unfortunately, building up is more expensive. Another thing that's helpful is alleys. If you put the garage behind the house, you don't need as much frontage width for driveways and garage doors.