ADU - Accessory Dwelling Units
These are small backyard houses that certain municipalities allow in order to mitigate the housing shortage. These may be interesting for OSE to build, as they are a legal exemption for building additional housing in urban areas. Thus, legal restrictions for building small, affordable houses are removed.
Encinitas offers free blueprints for ADUs: https://encinitasca.gov/pradu
This is a great, open resource. Plans were developed by hired architects.