One of the biggest fears Atlantans voice about urban density is that it will cause too much strain on our infrastructure. Whenever we discuss allowing apartments and duplexes into single-family home districts, neighbors push back with warnings that the water, electricity, and sewage systems will be strained.
To get the facts, we turned to Griffin Wasdin, a licensed Civil Engineer.
Is urban density in Atlanta a danger to our infrastructure systems?
[Wasdin]: “Honestly, density is the best thing for infrastructure, especially LINEAR infrastructure. Infrastructure is designed for long term durability in 15 to 100 year replacement cycles. Remember how your parents used to check that your shoes had room to grow in? Civil engineers do that with sewers and power lines too. Each urban block requires a minimum investment in asphalt, piping, sidewalks, power lines, transformers, telecom, etc, so each block is (almost) a fixed cost. More residents on a block just means more efficient utilization of this expensive upfront investment.”
“It is also important to remember that City of Atlanta’s population density is about 50% of the population density in the middle of the 20th Century when the majority of our modern infrastructure system was developed, so in many cases, today’s ‘increased urban density’ is simply returning to the infrastructure system’s original design conditions.”
Some people claim the old pipes in their neighborhoods can’t handle more stress; is it true?
“Strong Towns estimates that the typical North American urban neighborhoods could increase density by a factor of ten without impacting the existing sewer lines.”
“Fun fact: the Ductile Iron Pipe Research Association (formerly the Cast Iron Pipe Research Association) gives out an award for water mains that provide service for 100 years. They started giving out the award in the 1940’s and in the 1990’s the added a sesquicentennial award. Augusta, GA has at least one pipe still in service from 1859. Infrastructure done right is durable and resilient.”
What about our water and sewage infrastructure – can they handle increased density?
“A recent Strong Towns podcast touched on the issue of water supply versus demand, versus capacity. Modern pressurized water systems are designed to deliver high volume water service for fire fighting which is far, far greater than what is required for drinking water; yet another example of how existing infrastructure can easily accommodate infill development and higher density.”
“As for modern urban households, they use dramatically less water and energy per person, which means our aging systems are actually increasing excess capacity through efficiency. According to the Metropolitan North Georgia Water District, per-person water usage today (99 gallons per day) is down 50% from 2000. Our current Metro region’s wastewater treatment capacity (697 million gallons per day) exceeds the 2050 projected capacity needs (667 million gallons per day).”
And electricity? Can our grid support new density in Single Family Home districts?
“Electric utility service operates similar to the principles described above but with some caveats and nuances. Like water and sewer, intown Atlanta’s power delivery infrastructure was originally built back when our neighborhoods were 50% denser, so there’s some built-in capacity as we crawl back to historic population levels. Power-delivery equipment is installed in 20-40 year replacement cycles, so system planning engineers often oversize new equipment to leave a healthy margin for growth.”
“Unlike water and sewer, household power consumption doesn’t follow a clear downward trend. Downward consumption trends from increasingly efficient fixtures and appliances can be counterbalanced by new energy hogging technology like electric cars that system planners in the 1950’s would never have anticipated. Efficiency gains from modern heat pump AC systems and triple pane windows is offset by a long term change in consumers’ preference for increasingly colder indoor air temperatures.”
“The one ‘trend’ that is certain in residential power consumption is that multifamily homes will always be more energy efficient that single family homes, and really, it’s not so much a trend as physics. Multifamily homes tend to be more compact which results in a smaller space to heat or cool, and the presence of one or several party walls shared between units results in a lower heat exchange surface area with the hot or cold outdoor temperature extremes. Multifamily homes tend to be newer and built to a higher quality standard than single family homes, so their scant exterior walls tend to be better insulated (“better” here carrying a lot of water considering many historic Craftsmen and Victorian-era homes are completely uninsulated).”