If you have extra space in your home, garage or another structure on your property, you can convert that space into an Accessory Dwelling Unit (ADU). In this webinar, we were joined by architect Alex Tzang for an informative session on Conversion ADUs and Junior ADUs (JADUs) — a smart and cost-effective way to expand your living space or generate rental income.
Some takeaways
What is a Junior ADU (JADU)?
- Converted for primary dwelling or attached structure (like an attached garage)
- 500 sqft max
- Does not need its own bathroom, but must have access to one within the house
- Must have a kitchen, even if it doesn’t have a bathroom
- Exempt from parking requirements
- Typically do not need separate heating & central systems (e.g. HVAC, ducting) from primary house
- Owner occupancy is required in the main house or the JADU
What is a conversion ADU?
- Converted from existing structure (either habitable or non-habitable space, like a garage or a shed)
- Can be 800 sqft max or 50% of the main house floor area, whichever is larger
- Can trigger fire or sound proof requirements
- Must have separate heating and central systems from the main house
- Owner occupancy is not required
Value engineering your ADU conversion: how to get the most bang for your buck
- Limit what you are undoing and maximize what you are creating: For example, don’t move plumbing from existing location, plan around existing window openings
- Simplicity goes a long way: Trying to fit many elements (e.g. storage, hallways) into a space adds complication and cost – a clean and easy-to-follow design can go a long way
- Find professionals who have worked in the area: Jurisdictions have different rules and quirks – working with someone who has worked on ADUs and who knows how to navigate the local context can be very helpful
Typical project costs
- Simplest conversion ADU can start at $200 / square foot, not including finishes
- 2 car garage ADU conversion can cost ~ $400 / square foot (i.e. $120-150K)
- New detached ADU will start at around $400 / square foot (i.e. double the cost of the most simple type of conversion)
What to be aware of before you start your project
- Sewer lateral requirements can add costs to your projects. If your sewer lateral hasn’t been replaced in 20 years, you’ll likely need to replace it as part of your ADU conversion, which can cost $15-20K
- When ADUs touch other units (e.g., above/below or side-by-side), shared walls or ceilings must be fireproof and soundproof. Many contractors assume basic materials like fire-rated drywall and insulation suffice—this is incorrect
- For garage conversions: because garages usually touch the kitchen, fire/sound requirements can force removal of backsplashes or cabinets. Always ask your architect if the fireproof solution requires demolition
- When converting basements or garages to habitable space, shear wall retrofitting may be required. This includes anchoring to foundations, which can be complex if foundations are shallow. Ask your architect if the foundation
- Electrical panel upgrade may be required if your primary house is currently on a 75 amp electrical panel (e.g. this is the case for some older houses)
