I put some more thought into it and did some measurements and it makes way more sense than I initially thought. I looked at a random neighborhood in a large city nearish to me and it had 50-60 foot wide roads (and it seemed most of the roads with sidewalks the road itself was narrower but had a very similar ~60-70 feet sidewalk to sidewalk) and a narrow road with a traffic calming median had 10 foot wide lanes. Each of these neighborhood streets had an average of about 10 single family homes on each side, with roads about 1500 feet long (0.25-0.3 milesish, so a very short walk from end to end) most appeared to have 1 car garages with a few having 2 car garages
If we take on of those 60 foot wide streets, place a pair of small garages on each end with 6 parking spots each (parking spaces are 8x16 feet on average and this assumes a 16 food wide driving lane to access these garages) providing covered offstreet parking for 1.2 cars per existing household (makes the transition more politically palletable) which consumes about 160 feet of the 1500 feet of former-road and preserves a dedicated 10 foot wide alleyway (potentially with a 1 foot each side “keep out” space for emergency vehicles. Some fire engines are a bit more than 10 feet wide)
We’re left with a 1340 x 50 foot strip of land. If we break that into 50x100 foot plots you can fit a dozen double-wide manufactured homes (square footage of 800-2500 sq feet, just using manufactured homes as a consistent and easy example) with space for a yard for each of them. Alternatively if you do 50x50 plots you can easily fit a cute little 30x30-40 foot home on each plot with a small private yard and add 26 900-1200 square foot single family homes. You could even convert one or two of these plots into new green spaces to further make it a nicer neighborhood
In the example block I looked at, there were 3 very similar parallel streets squared off with other slightly higher throughput streets surrounding them. If we convert these 3 streets in this way, creating a dense walkable/bikable superblock we’ve taken an area of 1300x1500 feet that previously contained 60 single family homes, and increased that to about 135 homes without reducing anyone’s yards and only by shifting them to use a communal garage instead of a private one (which they can now convert their garages into living space and remove their driveways for more yard space!) Or we go from about 800 single family homes per square mile to over 1800 homes per square mile. And this is just unimaginative replacing existing roads with single family homes and not even considering adding any sort of mixed use or multifamily homes1 nor annexing any portion of the existing homes’ 50 foot deep front yards!
If we annex 30 feet existing homes’ 50 foot deep front yard (they still keep their 50 foot deep backyards!) that gives us about 120x1500 feet to redevelop. Lets put a 10 foot wide alleyway on each side in front of the existing homes, drop the shared garages because nobody loses road access, and we’ve got 100x1500 feet to work with, or easily 60 new 50x50 foot plots or 74 40x50 foot plots (240 or 282 homes where there was previously 60, alternatively 3400 or 4000 lots per sq mile up from ~1800 originally)
1. I did calculate out 2900 48 units in the 50x1500 foot space using 100x40 foot quadplexes
I put some more thought into it and did some measurements and it makes way more sense than I initially thought. I looked at a random neighborhood in a large city nearish to me and it had 50-60 foot wide roads (and it seemed most of the roads with sidewalks the road itself was narrower but had a very similar ~60-70 feet sidewalk to sidewalk) and a narrow road with a traffic calming median had 10 foot wide lanes. Each of these neighborhood streets had an average of about 10 single family homes on each side, with roads about 1500 feet long (0.25-0.3 milesish, so a very short walk from end to end) most appeared to have 1 car garages with a few having 2 car garages
If we take on of those 60 foot wide streets, place a pair of small garages on each end with 6 parking spots each (parking spaces are 8x16 feet on average and this assumes a 16 food wide driving lane to access these garages) providing covered offstreet parking for 1.2 cars per existing household (makes the transition more politically palletable) which consumes about 160 feet of the 1500 feet of former-road and preserves a dedicated 10 foot wide alleyway (potentially with a 1 foot each side “keep out” space for emergency vehicles. Some fire engines are a bit more than 10 feet wide)
We’re left with a 1340 x 50 foot strip of land. If we break that into 50x100 foot plots you can fit a dozen double-wide manufactured homes (square footage of 800-2500 sq feet, just using manufactured homes as a consistent and easy example) with space for a yard for each of them. Alternatively if you do 50x50 plots you can easily fit a cute little 30x30-40 foot home on each plot with a small private yard and add 26 900-1200 square foot single family homes. You could even convert one or two of these plots into new green spaces to further make it a nicer neighborhood
In the example block I looked at, there were 3 very similar parallel streets squared off with other slightly higher throughput streets surrounding them. If we convert these 3 streets in this way, creating a dense walkable/bikable superblock we’ve taken an area of 1300x1500 feet that previously contained 60 single family homes, and increased that to about 135 homes without reducing anyone’s yards and only by shifting them to use a communal garage instead of a private one (which they can now convert their garages into living space and remove their driveways for more yard space!) Or we go from about 800 single family homes per square mile to over 1800 homes per square mile. And this is just unimaginative replacing existing roads with single family homes and not even considering adding any sort of mixed use or multifamily homes1 nor annexing any portion of the existing homes’ 50 foot deep front yards!
If we annex 30 feet existing homes’ 50 foot deep front yard (they still keep their 50 foot deep backyards!) that gives us about 120x1500 feet to redevelop. Lets put a 10 foot wide alleyway on each side in front of the existing homes, drop the shared garages because nobody loses road access, and we’ve got 100x1500 feet to work with, or easily 60 new 50x50 foot plots or 74 40x50 foot plots (240 or 282 homes where there was previously 60, alternatively 3400 or 4000 lots per sq mile up from ~1800 originally)
1. I did calculate out 2900 48 units in the 50x1500 foot space using 100x40 foot quadplexes