I am very skeptical of both the surveys quoted in this article and the purported benefits this legislation is supposed to produce.
Nobody wants their street to switch from single family homes to quad housing units. Nobody. Well, the only people who might want this would be those who are intent on moving elsewhere and want to maximize rental revenue. I would definitely do this because we would go from a singe rental revenue stream to four or five (the law sounds like you can build four additional units).
The fallacy here is that rental rates don't come down as a function of n --n defined as the number of units on a lot. It isn't a linear relationship at all. If I had to guess, the rental cost per unit might be somewhere around 50% to 80% of what one might get by renting the entire home as a single unit. Taking the low side on that and assuming we build 5 units, this means the gross rent income for the property just went up 2.5x to 4.0x. If construction costs fit the model, this could be a great deal.
Nobody is going to rent one of these units for less than the prevailing rent for similar units in existing apartment buildings. So, no, rents will not come down by a significant margin.
The other angle is to just build an n-plex and sell the units. My guess on that one is that you'll make far more on the property than if you sold the single family home. I would further postulate that the cost per unit will track with comparable properties and will not really make things more affordable. I mean this in the sense that you are going to pay per square foot whatever anyone is paying per square foot elsewhere in the area. This law will not magically create a 50% discount per square foot. One of the reasons for this being as simple as: Construction, materials and permit costs keep going up, not down. In very rough terms, construction costs are in a range between $150 and $400 per square foot (depending on location, design, quality, low-end, high-end, etc.). That quickly becomes a very real lower bound on property valuation. The ONLY way to make home more affordable is to, at a minimum, reduce construction, regulatory and permit costs.
And then there's the issue of what happens to a street and a neighborhood when you multiply the population by four or five. I am trying to imagine my street with 5x the vehicles. It is unimaginable. However, it goes beyond that. The sewage system, power, gas and water distribution systems were not designed to support five times the demand.
Simple example: Our water comes from a large water tank atop a hill serving this neighborhood. That tank, while large, was sized based on regional planning approved many decades ago, which, of course, consisted of single family homes almost exclusively. There is no way this tank and the system that feeds it (pumps, aqueduct, etc.) is sized to support a 5x growth in demand.
Similar issues with power and other utilities.
Then there's the issue of traffic. We already have high traffic density and glorious traffic jams in the immediate region on a daily basis. A 5x explosion in population would turn this into nothing less than a living hell experience. Here's a data point. Many years ago I had to drive 50 miles to go work at a client's facility. I did this for two years. When the contract started I could do the 50 miles in about 45 minutes --so long as I left at 6:00 AM. Towards the end of the contract it was taking 2 hours. If I left at 5 AM I had a chance to cover the distance in an hour. A few minutes later and it got ugly quick. It was not uncommon to spend three hours on the road to get back.
I won't even go into the likely in increase in crime. No, this isn't a judgement on the quality of people who would move in. It's a simple reality, increase the population five-fold and you will have an increase in crime. Simple example: More cars parked on the streets means lots more opportunities to break into them for profit.
The consequences of these effects are very easy to predict. In our case, if I saw this transition happening, we would likely build our five units, rent or sell them and get the fuck out. Seriously. I am going to watch this like a hawk. My guess is the potential exists for entire neighborhoods to turn into multi-plex hellholes. Lots of people will make a lot of money by making the right move at the right time. Others will be left in limbo. And residents will be treated to expensive, stressful and substandard living conditions.
This is also as far from "green" and "sustainable" (in quotes because these terms are becoming jokes) as one can get. What you want is sparse population fed by a solar grid and serviced by equally sparse commercial and employment centers (not centralized as a place like LA can feel) and real improvements to mass transport. Why does someone from Lancaster or Riverside have to travel to LA or Santa Monica for work? That's the real problem. What we need are incentives for businesses to spread out. Home construction will follow and will likely become more affordable as a result.