Double Duplex

 

Time period: mid-late 2010s, 2020s
Location: Los Angeles

The double duplex is a rooming house pretending to be a bunch of houses. 

Key features
- Four homes, each with 4 or 5 bedrooms that are designed to be rented out to 16-20 separate households.
- Since each building only has two homes, it's built to the simpler standards of the Residential Code instead of the Building Code.  This simplifies approvals, saves costs, and means more small contractors know how to build them.
- Since it's technically only four units, it doesn't need to provide as much parking.

The double duplex is a pair of duplexes on a single residential lot.  In South LA and Central LA, where this type of housing was invented, it is a pair of boxy 3-story buildings on a 50' wide x 150' deep lot, replacing an older house.  

These are not fancy buildings. While rents in California are high, so are construction costs, and every expense is spared when it comes to designing a double duplex. After all, this is housing designed to have as many bedrooms as possible while just barely meeting the zoning and building codes. The buildings are a cube, to maximize the amount of indoor space while minimizing the amount of wall and roof.  Windows are small and typically of the cheapest vinyl type available.  

Also, duplexes are built to a simpler code than 3+ unit buildings. Most of the time, the building code requires more safety features for larger buildings, based on number of floors, total square feet, or expected number of people in the building at one time. This makes sense. However, there's an easier set of regulations for houses and duplexes. A mansion, or a duplex designed for 20 roommates, has lower standards than a building with three studio apartments for 3 people. This does not make sense. As a side note, always know how to get to an exit when attending a party in a large house. There might only be one, there won't be any exit signs to guide you to it, and the doors and hallways are not going to be sized to handle dozens of people.

Here's the business model for double duplexes:
1. Build a double duplex with a four units, each with five bedrooms, 20 rooms total
2. Rent out to 40 college students, 2 to a room.
3. Profit

Developers reuse plans, but since this is an infill housing type, you won't see entire tracts of identical double duplexes, instead, you might find yourself doing a double take upon seeing the same building a block away.

Typical double duplex site plan.  Note that the front duplex is narrower, in order to fit the driveway.
 
While each of the four homes in a double duplex could be occupied by a large family, in practice they're designed to be rented out by the bedroom - a double duplex property can have 20 different leases. Rents are less than that of a regular studio apartment.  Double duplexes are popular with students, young individuals, and working class families.  
 
They are most common around the University of $outhern California, which has a student housing shortage and also is surrounded by low density multifamily zoning.  In contrast, the area around UCLA is either high density multifamily or single family zoning, so most of the new housing there is mid or high rise.

Each bedroom usually has its own bathroom, so it can rented out as a suite. Bedrooms are large enough for 2 people. Some double duplexes have indoor garages, while others only have outdoor parking.   

 
California law allows garages, storage, and other utility spaces in an existing multi-unit building to be converted into an Accessory Dwelling Unit.  Once a new building is complete, it's considered existing :)
 
That's how a Double Duplex then becomes a Double Triplex, for even more profit.

In 2021, the California State Legislature passed Senate Bill 9, which allows up to four homes to be built on lots previously zoned for only one house.  However, SB9 has many restrictions and as of 2023, has not yet resulted in a major construction boom.  These restrictions include requiring the lot to be split into two lots in order to build four full-size homes and requiring the owner to live on site to split the lot.

Data
- Density: 23 units/acre (+/- 100 rentable bedrooms/acre)
- Typical Lot Size: 7,500 square feet (50'x150')
- Typical Zoning: Low Density Multifamily, Restricted Multiple Unit
- Construction Type: V (Wood frame)
- Resident Type: Rental, by the room

Where to build
- Near colleges
- Places where there is unmet demand for studio apartments

Further Reading

Article on why developers are building double duplexes instead of regular apartment buildings: https://www.livablecommunitiesinitiative.com/blog/support-ab-835-a-single-stair-bill-to-make-housing-better-more-affordable-and-safer

Example of a double duplex https://www.compass.com/listing/1805-south-new-england-street-los-angeles-ca-90006/831974667202603817/

Another example, this one is a triple duplex https://www.compass.com/listing/1818-thurman-avenue-los-angeles-ca-90019/835651210280874841/ 

Text of Senate Bill 9: https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202120220SB9

Data on usage of SB9 one year after it took effect: https://ternercenter.berkeley.edu/research-and-policy/sb-9-turns-one-applications/

Example of how to use SB9: https://planning.lacity.org/project-review/senate-bill-9

More info on how to use SB9: https://sites.google.com/view/alfredtwu/infographics/sb9

2019 Accessory Dwelling Unit law AB68 https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=201920200AB68

Comments

Post a Comment

Popular posts from this blog

Point Access Block

Image
Time period: Late 19th and early 20th century, revived in 21st century. Location: Used to be everywhere.  Today: Seattle and New York City. A mid-rise building with a couple apartments on each floor.   In most cities, you'll find two types of mid-rise apartment buildings in the 4-7 story range. First, there'll be some small historic buildings downtown, side by side like books on a shelf. These are the original point access blocks. Then, there are the big modern buildings taking up a whole block and with long, windowless hallways inside. These are double loaded corridor buildings. Floorplan of a point access block.   Note that apartments have windows facing the front and back of the building.     In contrast, except for the corner units, apartments in a double loaded corridor only have windows facing one direction. Both the point access block and the double loaded corridor were designed to be the most efficient floorplan given the building codes of th...
Read more

Dingbat

Image
  Time period: 1950s-1960s Location: Los Angeles and other cities in the Western US 6+ homes and parking spaces, all on a standard house-sized lot, named after the fanciful decor tacked onto the front.  The dingbat was invented in post-WWII Los Angeles to meet the housing needs of a growing city as well as growing rates of car ownership. The standard 50' wide, 150' deep LA lot had been gridded out for detached houses, but many were zoned for low-rise apartments. Before the dingbat, the most popular types of medium-density housing were bungalow courts - a series of houses around a central walkway, as well as multistory courtyard apartments. In 1934, both types were banned by a new zoning law that required parking: one space per unit. Developers solved this math problem by turning the front yard into a driveway, leading to a carport that took up the front of the first floor. To maximize space, the second floor extends over the carport, propped up on stilts. This type of structur...
Read more

Fourplex

Image
Time period: 1890s-1920s, 1960s-1980s, 2020s to present day Location: Suburbs nationwide The classic US fourplex is a 2-story building with four apartments: two upstairs, two downstairs. First becoming popular when streetcars (also known as trolleys or trams) made suburbs possible, the fourplex offers choice for households who want to get out of the crowded city but can't afford or don't need a standalone house. Cross section of a fourplex . Before streetcars, city dwellers lived within walking distance of the city center. Few people could afford horses, so walking speed limited the physical size of cities. Adults walk at 2-3 miles per hour, which meant the largest ancient and medieval cities were just a couple miles wide. When population grew, cities would grow upwards, replacing houses with townhouses and tenements, 3-7 stories tall, built right next to each other with walls touching. Streetcars were invented in 1887 and could go much faster. Even with time waiting at traffi...
Read more